Pottery Making illustrated 1

2 Fall 1998

Cover: Pot, 4¾ inches in height, pit fired, by Martha Puckett. Photo by Ginny Marsh. See story p. 23.

Pottery Making illustrated 3

Kitchen Safeby Greg Geiger...........................................................................................6Test your ware for microwave and dishwasher use.

Building a Portable Gas Kilnby George Juliano with Elizabeth Hudgins.................................................9Build a great little kiln that will fire most anywhere.

Successful Raku Firingby George Juliano with Elizabeth Hudgins.............................................. 13Tips and technique for getting great results from your raku firing.

Volumetric Glazingby Sumi von Dassow................................................................................ 17No scale? No problem when mixing glazes by the cup.

Throwing Tall Potsby Ivor Lewis........................................................................................... 19The philosophy, theory and practice of adding height to your work.

Martha Puckett s Porta-Kilnby Ginny Marsh....................................................................................... 23Getting started in sawdust firing is simple with this easy-to-build kiln.

Overlapping Glazesby Harold Hart........................................................................................ 30Multiply your glaze repertoire with overlapping patterns.

Tile Settersby Barbara Coultry .................................................................................34Make your own tile setters with these easy-to-follow instructions.

Slab Potteryby Norman Holen.................................................................................... 37Step-by-step procedure from paper design to completion.

Little Peopleby Craig Hinshaw....................................................................................42Second and third graders strike a pose and preserve it in clay.

Prop It Upby Barbara Coultry .................................................................................45Propping your work is easy with stilts you can make.

Editor: Bill JonesAdvertising Manager: Steve Hecker Production Manager: Thom Misiak Graphic Design: Debi Hampton Graphic Production: Robin Chukes Circulation: Mary Hopkins Publisher: Mark MecklenborgEditorial, Advertising & Circulation Offices735 Ceramic Place PO Box 6136Westerville, OH 43086-6136 Phone: (614) 794-5890 Fax: (614) 891-8960 E-mail: potterymaking@acers.org Web Site: www.potterymaking.orgPottery Making Illustrated (ISSN 1096-830X) is published quarterly by The American Ceramic Society, 735 Ceramic Place, Westerville, OH 43081. Standard mail (A) postage paid at Westerville, OH, and additional mailing offices. Opinions expressed are those of the contribu­tors and do not necessarily represent those of the editors or The American Ceramic Society. Subscription Rates: One year $15, two years $27, three years $36. Add $8 per year for sub­scriptions outside North America. In Canada, add GST (R123994618). All payments in US dollars. Allow 6-8 weeks for delivery. Advertising: Ad rates and ad information are available on the web site or by contacting Steve Hecker at the address above or by phone at (614) 794-5809.Change of Address: Send your magazine ad­dress label along with your new address to the Circulation Department. Allow six weeks ad­vance notice.Contributors: Writing and photographic guide­lines are available on request. Mail manuscripts and visual materials to the editorial offices with a self-addressed postcard for notification of receipt. Indexing: Feature articles are indexed in the Art Index and daai (design and applied arts index), available through public and university libraries. Photocopies: Permission to photocopy for per­sonal or internal use beyond the limits of Sec­tions 107 and 108 of the U.S. Copyright Law is granted by The American Ceramic Society, pro­vided that the base fee of US$5 per copy, plus US$0.50 per page, is paid directly to the Copy­right Clearance Center, 222 Rosewood Dr., Danvers, MA 01923 USA (508) 750-8400.This consent does not extend to other kinds of copy­ing, such as copying for general distribution, for advertising or promotional purposes, or for cre­ating new collective works. Requests for special photocopying permission and reprint requests should be directed to the Director of Publica­tions, The American Ceramic Society, PO Box 6136, Westerville, OH 43086-6136.Back Issues: When available, back issues are $5 each, plus $2 postage. Add $5 for orders outside North America. In Canada, add GST (registration number R123994618). Postmaster: Send address changes to Pottery Mak­ing Illustrated, 735 Ceramic Pl.,PO Box 6136,West­erville, OH 43086-6136. Form 3579 requested.

Copyright © 1998 All rights reserved

Fall 19984

Pottery Making illustrated 5

KITCHEN SAFEby Greg Geiger

QuestionWhat is meant by the term “microwave safe” and “dishwasher safe” and what are the criteria and standards used to determine and test for this?

Aiccording to an experienced ceramics con­sultant, Dick Eppler of Eppler Associates, “micro­wave safe” basically means that the product in question has to be free of electrically conducting materials (i.e., metals).The main concern here is with electrically conducting decorations, such as gold, on the outside of the ceramic piece.

When a ceramic or glass piece with an electrical­ly conducting decoration (e.g., gold) is exposed to the energy field in a microwave oven, it exhibits a rapid rise in temperature (self heating) and an arc­ing effect, which extensively cracks the decorative film. This most often results in a substantial loss of the film’s decorative appeal and a diminished dura­bility in subsequent use. This high temperature of the ceramic ware may also cause harm to the con­sumer in the form of a burn.

According to Eppler, and Meg Nichols of ACTS Testing Labs, Inc. (a commercial testing laboratory), there are no standards for this classification. Nichols states that each company performs its own test, such as cycling the ware through the microwave 10 or more times, and that it is up to the company or in­dividual to determine its safety in this area.

Cookson Matthey Ceramics, Inc., a leader in decorative and surface finishing materials for the glass and ceramics industries, tests microwave resis­tance by placing the decorated object in a conven­tional microwave, on high, for 2 minutes.The deco­ration must not arc nor produce any self heating (they check every 30 seconds) and no conductivity (they measure resistivity).

Marta Pilat, Technical Service Manager for Cookson Matthey, reports that the type of body used in the preparation can affect the microwave re­sistance. Porous bodies, after prolonged use (i.e., dishwasher washing, etc.), in which glaze wears off, will begin to slowly absorb moisture. In a micro­wave, the ware will be subjected to the energy of microwaves and a superheated steam may be pro­duced. The end result will be breakage of the ware during microwaving. Vitreous bodies, on the other hand, are less likely to have this problem.

Pilat also noted that glazes do not have conduc­tive properties since the frit fires to a glass finish, thus shielding the metal from microwaves. Also, metals are normally present in minimal amounts, but are not forming a continuous layer, thus con­ductivity is prevented.

Microwave Safe6 Fall 1998

KITCHEN SAFE

^^ishwasher safe can mean one of two things: It can be used to describe a ceramic piece that can stand up mechanically (i.e., not break) during a dishwashing cycle. Or it has to do with the ability of the ceramic decoration or glaze to stand up to repeated washings in the dishwasher without losing its original appearance (i.e., no fading or dulling), which is also known as “detergent resistance.”

Cookson Matthey Ceramics, Inc., tests the detergent resistance by immersing the decorated glass or ceramic piece in a detergent bath at 208°- 212°F for 90-minute intervals. The company requires that the decoration stay on for 3 consecu­tive cycles (total of 270 minutes) without enamel/ gold removal. They additionally use the American Society for Standards and Materials (ASTM) C676- 93* to test the dishwasher resistance.

ASTM C676-93 Detergent Resistance of Ceramic Deco­rations on Glass Tableware This qualitative test method is designed to

provide a convenient and reproducible method of determining the detergent resistance of decorations applied to glass tableware.

Another company, Engelhard Corp., tests the detergent resistance (or dishwasher safety) by exposing the ceramic ware in a boiling solution of0.5% sodium carbonate and noting how many minutes it requires to reach 80% loss of film (gold decoration, in this case) coverage.

While these are a couple test methods used to determine the detergent resistance, they do not set acceptable limits of what is considered “dishwasher safe.” This determination is left up to the manufac­turer or the individual potter.

According to Eppler, detergents used in dish­washers are pyrophosphates, thus ASTM C614* could be an appropriate test to use. Though written for porcelain coatings, the test would also be applicable to pottery.

ASTM C614-14(1980)el Alkali Resistance of Porce­lain EnamelsThis test method covers the measurement of the

resistance of a porcelain enamel to a hot solution of tetrasodium pyrophosphate. Although the specific alkali mentioned herein is tetrasodium pyrophos­phate, the equipment and techniques are equally applicable to other alkali solutions.

*The American Society ofTesting Materials (ASTM) sells tests through its web site at http://www.astm.org

For the studio potter, there are no definitive tests for microwave safe and dishwasher safe other than that of experience. Since commercial producers make claims for the durability of their products, studio potters need to know the durability of their own ware, especially if they are giving it as gifts or marketing it to the public. Testing can be as informal as using pieces in a normal day-to-day setting in a kitchen, or putting samples through their paces in a structured test.

Greg Geiger is a ceramic engineer and manages the Ceramic Information Center (CIC) for The American Ceramic Society in Westerville, Ohio.

Pottery Making illustrated

Dishwasher Safe

Conclusion

7

Fall 19988

A portable gas kiln was difficult to find within our budget, but the school needed one if my students and I were going to experiment with raku firing. I decided that the kiln had to be simple to operate, light, easily movable, safe and effective. After doing some research and shopping, I determined that I could build one that would meet all of my criteria for a lot less than I could possibly purchase one. So, with the help of the auto mechanics teacher at my school, I set out to build the kiln.

Figure 1Take a 55-gallon oil drum and clean it thoroughly with Varsol. Once it’s completely clean and dry, use a reciprocating saw with a metal cutting blade, and cut the drum just above the second rib (about 24 inches from the base to the rim). Cutting above the rib provides extra strength and stability to the rim.

Figure 3

Bolt 3 metal “spider legs” to the drum lid, using 2 bolts for each leg. Make legs from 2-inch-wide by 1/4-inch-thick strips of metal, and bend them over the edge of the lid so that 3 inches remain on the top while 8 inches of metal hang over the edge. Set the metal strips at a slight angle away from the vertical sides of the drum when you place the lid on the drum. The legs add some stability for the lid when it’s in place, but they shouldn’t get in the way of putting the lid on or taking it off. The major purpose of the legs is to hold the extremely hot lid off the ground when removing pots from the kiln. The legs allow air to flow under the lid, preventing it from destroying blacktop or grass.

Tip: In addition to the legs, bolt 2 handles onto the lid about 3 inches from the edge so you can easily grab and lift the lid to remove raku pieces. Also, bolt 2 handles on the sides of the drum at a comfortable height for picking up and moving the kiln. This is important if you need to take the kiln inside between uses.Note: To provide the smoothest surface on the inside of the kiln, install all bolts with the head on the inside so the thread and nut are on the outside.

Pottery Making illustrated

Figure 2Next, use the saw to cut a burner port 3 inches from the bottom, making a hole 3½ inches square. This hole is where you’ll direct the burner when you fire the kiln. Finally, cut a 4-inch-square hole in the center of the lid and drill four ½-inch holes 2 inches from the center of each side of the square.CAUTION: File all cut metal edges smooth to avoid injury.

by George Juliano with Elizabeth Hudgins

9

Figure 4

To insulate the inside of the kiln, use 1-inch-thick fiber-insulating blanket, which is carried by most pottery supply stores. Cut 2 circles, 1 to fit the lid and 1 to fit the bottom of the drum. Also cut a large rectangle so that the length measures the same as the circumfer­ence of the drum, and the width equals the height of the drum. Carefully place the fiber into the drum to make sure that it fits snugly with no gaps. Be careful not to press on the fiber since compression of the fibers diminish the effectiveness of the insulation. Once you’re certain of a snug fit, remove the fiber-blanket pieces and coat the inside of the drum and the underside of the lid with sodium silicate. Let that set for a minute or two, then gently push the fiber back in, again avoiding pressure so that the blanket remains fluffy. After the insulation is in place, carefully cut the fiber blanket out for the burner port and put the piece aside for later use.CAUTION: Fiber from fiber blankets can irritate the eyes, nose, throat, lungs and skin during installation and use. Always wear protective clothing and gloves, and use a respirator according to manufacturers’ recommendations.

Figure 5

For the lid hole, carefully cut the fiber at an angle from corner to corner so that you can fold the triangles out and over the sides of the square. This enables you to cover the edge of the metal on the square so that there is insulation all around the hole. The insulation keeps the lid temperature down a little. Insert bolts through the lid from the inside through the four holes drilled earlier and through the triangular tabs. The bolts make it less likely that the fiber blanket on the lid will respond to gravity and fall off after a number of uses.

Figure 6Cut small circles out of the fiber-blanket scrap you saved from the burner port hole. Place the circles over the bolt heads on the inside of the lid, using sodium silicate. Set the finished kiln on three concrete blocks, one of which is located directly under the burner port. The blocks provide stability, keep the kiln off the ground and allow for a greater flow of air once the kiln is firing.

Figure 7

Take three shelf posts and a round shelf to make a platform for the pieces to be fired. Place the three posts so that one of them is angled (with a corner facing the center of the burner port). Angling the post disperses the flame to both sides for more even heat distribution. Place the shelf just above the burner port.

BUILDING A PORTABLE GAS KILN10 Fall 1998

BUILDING A PORTABLE GAS KILN

Figure 11To add even more stability, brace 2 bricks against the burner to create an A-frame “tent” for it. (I’ve been glad I did this. Several times someone has walked by and accidentally hit the hose, but the burner wasn’t dislodged, thanks to the channel and the A-frame secu­rity.) Place the burner head 1 inch from the burner port. This allows for oxygen to enter the kiln with the flame, making for a hotter fire in the kiln.

Figure 12Finally, remove the top and bottom of an empty coffee can and place it on top of the lid to serve as a chimney for the kiln.

Figure 8

This portable kiln can be fired with propane or natural gas. I fire my kiln with propane, and I purchased a burner system. In addition, I picked up a 10- foot-long hose, a fitting for the connec­tion between the hose and a propane tank, a propane tank such as those used for gas grills, a tub to put the propane tank in, a valve cock, and a pressure regulator. Attach the pressure regulator to the hose and then the hose to the fitting for the propane tank.Tip: Since the propane tank tends to ice up when the kiln is firing, place the tank in a tub of water. This seems to keep the icing down a bit, making the flow of gas smoother and the firing more consistent.

Pottery Making illustrated

Figure 9Attach the other end of the hose to the valve cock and then to the burner. Place another cement block in front of the one you placed under the burner port. Use this as the base for the burner.

Figure 10To stabilize the burner, I cut a common building brick (with two holes in it) so that the brick could stand on one end, providing a nice U-shaped channel to lay the burner in.

I I

SUCCESSFUL RAKU FIRINGHaving been interested in raku

firing for years, and knowing that potters often lose as much as 40% of their raku pieces in the process,I decided to do some experiments to try to make my raku firing pots more productive. I first built the portable gas kiln (see p. 9), then started looking at the handling of the pieces. Even though I found that allowing 24 hours minimum between the glazing and the raku firing significantly cut down on my losses, I still had a less-than-acceptable loss rate, so I continued my experiments.

Raku can produce such beautiful results. Now; with a few modifica­tions in the methods used, nearly every piece can come out both beautiful and whole. Here's how I do it.

PROCEDUREI set 3 shelf posts on the floor of the raku kiln (figure 1 on page 15). I make sure that one of the posts is set in the center of the burner hole so that it s angled with the corner facing the hole. I do this to spread the heat. Next, I place a round shelf above the burner hole (figure 2).I place the glazed pots on the bare shelf with about ½-inch clearance between each piece and between the pieces and the fiber-blanket wall (figure 3). I found that a 2-inch clearance from the top of the kiln also helped. If I placed a large piece in the center, I found that this would stop the air flow and, in addition, make it hard for me to see into the kiln to check on the progress of the firing, so I moved the largest pieces to the sides. I also made a collar extension out of an­other section of oil drum, which I use for tall pots as needed.Before using the burner, I make sure the valve cock is closed and then fully open the propane tank valve. I slowly turn on the regulator (which measures pounds per square inch (PSI)), increasing the pressure until the needle touches the first line on the pressure regulator. With a long lighter (like the type used for lighting gas and charcoal grills) just in front of the burner, I open the valve cock on the burner until the gas ignites. I check to make sure that the flame is going under the kiln shelf and that the flame is diffused by the shelf post.I keep the flame low for 10 minutes and turn the regulator up to the next line. Then every 5 or 6 minutes, I advance the flow of fuel to the next line until I get to at least 5 on the regulator but no more than 7. After I have taken the burner to the highest level of pressure I want, I check the progress of the firing after about 5 to 10 minutes by carefully peeking into the coffee-can chimney.I frequently use a large Cone 07 as an indication of when the temperature has been reached (note cone positioning in figure 3).CAUTION: A raku kiln is extremely hot. When looking into the kiln, use protective eyewear (I suggest that you use welder’s goggles with a face shield). I’ve singed my hair and eyebrows upon occasion at this juncture.

12 Fall 1998

by George Juliano with Elizabeth Hudgins

1

2

3

4

I check the pots with the gloss glazes. If they are bubbling and boiling and are, frankly, rather ugly, I wait. Only when they stop bubbling and begin to smooth out like glass and the pots are glowing red on the inside do I feel that they are ready to come out. If the pots pass both tests and the cone has responded, I go to the pressure regulator and turn it all the way down, then I shut off the propane tank and, finally, turn the valve cock off at the burner.Using kiln gloves, I remove the coffee-can chim­ney. Then, using the handles on the kiln lid, I remove it and place it on the ground on the “spider legs” so that it won’t destroy the blacktop or grass. With raku tongs, I pick up each piece and place it in either a prepared raku pit or metal container. I remove the matt-glazed pieces first and put them quickly into the sand pit containers.I have 3 metal garbage cans and 8 raku sand pits. I made my pits with metal linings and then built up sand around them so that I can put the piece in the pit, place the lid on the container, and then scoop sand all around the lid so that no air can get in or escape (see figure 4).This makes an airtight container and is best for getting vivid colors or, as I prefer to say, “colors with an atti­tude”—especially the matt glazes.This airtight seal allows for heavy reduction. If, however, you are looking for more smoked and crackle effects on your gloss glazes, use the metal garbage cans. The lids on them will emit smoke and never have an airtight seal.

7

8

I place only one pot at a time in a pit or can. I prepare the containers by filling the bottom with loosely shredded newspapers and straw or sawdust. To avoid scarring on the gloss glazed pieces, I put the shredded newspaper and sawdust in and then place a coffee can with both ends removed on top of the shredded material. I fill the can with the same combustible material. I then place a metal grill from a barbecue grill on top of the coffee can and add a square of cardboard on top of that. The grill adds stability, and when the pot is placed on top, it won’t tip over. I then place shredded paper all around the sides and cover with the can lid.The cardboard ignites first, then sets the newspa­per on fire. The pot, however, won’t touch the newspaper and will be free of marks. After 2-3 minutes, I take the lid off (WARNING: Be careful at this point since the flames will jump way up!) and quickly throw more paper on top of the pot. This causes more carbon smoke and increases the darkness of the black cracks in the glazes. If you desire scarring, don’t use the square of card­board. By the way, I like to use newspaper since it gives the strongest blacks. Adding seaweed (the kind that can be purchased dry from Asian mar­kets) seems to increase the brilliance of the me tallies. Waving the pot in the air before putting it into the metal cans increases the amount of crackling on the glazes.After about 15 minutes, I take the pots out of the pits or garbage cans one at a time with my kiln gloves. I do not use the tongs here as I have better control with my hands. Most breakage occurs in this next step. Some potters use a large container of water and dip the piece in immediately to stop the reduction. I’ve found that the pots get shocked at this point if they are dipped. One area gets colder much faster than the rest of the piece, and this causes the breakage. I discovered that I could use a garden hose with a diffuser spray nozzle to cool the pots just as fast and lock in my colors, without shocking one portion of the pot more rapidly than another. I have an assistant using the hose with a gentle, wide spray. I place the pot quickly on a cinder block. As soon as it is standing on the cinder block, my assistant begins spraying in a rapid circular motion all around the pot. This acts like a rapid, gentle, rain on the pot. After 6 to 8 circles, the assistant fills the pot with water. This process allows much less shock on the clay, saving nearly all our pieces.

SUCCESSFUL RAKU FIRINGPottery Making illustrated 13

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6

You may also want to try a few of these glazes from the Ceramics Monthly archives. Ed.

Clear Raku Glaze(Cone 06)

Gerstley Borate.................. 70%Plastic Vitrox Clay............. . 30

100%Works well with underglazes and colored slips. (John Ramer Sherrill, CM, May 1996)

Roger’s White Glaze(Cone 08)

Gerstley Borate.................. 60%Spodumene........................ 35Tennessee Ball Clay......... .....5

100%This is actually a clear (not white) base recipe. It can be used as is or you can add colorants on an experimental basis. Add 5% tin oxide for a white glaze. (From Steven Branfman, PMI, Jan. 1994)

Tomat’s Red Raku GlazeBorax.................................. 50%Gerstley Borate................. . 50

100%Add: Copper Carbonate..... 40%

Red Iron Oxide.......... 10%Apply to the inside of a pot (From Brother Don Smith, CM, Nov. 1994)

Copper StainFrit 3110 (Ferro)................. 10%Copper Carbonate.............. 90

100%Apply stain to pot then wipe off with a sponge leaving stain just in the crevices. Coat with Piepenburg’s Clear. (From Brother Don Smith, CM, Nov. 1994)

Piepenburg 50-50Frit 3134 (Ferro)................. 50%Gerstley Borate................. 50

100%

Raku Copper Matt FinishRed Copper Oxide............. 78%Red Iron Oxide................... 9Frit 3110 (Ferro)................ 13

100%Adding a drop or two of dishwasher deter­gent to the liquid batch facilitates mixing. (From Robert Sunday, CM, April 1994)

Raku Clear Base GlazeGerstley Borate.................. 67%Frit 3403 (Ferro)................. 8Nepheline Syenite.............. 17Kaolin................................ 8

100%For color variations, add 10% commercial stain. (From Robert Sunday, CM ,April 1994)

Hasselle Copper MattBlack Copper Oxide........... 80%Ball Clay............................ ..20

100%Add: Bentonite.................... 2%(From Bob Hasselle, CM, Jan. 1997)

A clear glaze. Apply over stain. (From Brother Don Smith, CM, Nov. 1994)

successful raku firing14 Fall 1998

GLAZESDifferent glazes need different handling from initial

application through final cooling. For example, if I want an orange-peel texture when using a matt glaze,I dip the pot twice because the effect requires a thicker glaze. Many of the raku glazes are more effective, however, when put on thin. I find that dabbing matt glazes on with a sponge, using two coats, gives me the greatest results in terms of brilliance. The

Soldner Clear glaze is best dipped twice and reduced in the garbage can. The heavy application gives wider crackles on the surface, whereas a thin application gives a finer network of crackles. Experimentation and keeping a journal of results is the best teacher.

Here are recipes for some well-known glazes that I use, and general comments about the colors and effects of each.

Soldner ClearGerstley Borate...................... 80%Nepheline Syenite.................. 20

100%I feel this glaze looks best when applied thickly. I brush on at least four coats, pour on a thick application, or dip the piece twice. This generally results in wider-spaced crackles in the pottery. When I desire a finer network of crackles, I apply the glaze in a thin coat. After the glaze matures, I place the fired piece in a lidded trash can filled with newspapers. This causes an abundance of smoke so all the crackles are filled with a nice black (see figure 5).

Copper LusterGerstley Borate...................... 80.0%Nepheline Syenite.................. 20.0

100.0%Add: Cobalt Oxide.................. 1.1%

Copper Oxide................ 2.1%Yellow Ocher................. 7.8%

This glaze looks best when applied thin. I generally dip the pot once in a thin mixture. The glaze has a dark cranberry luster in appearance. I place pieces glazed with Copper Luster in a lidded trash can filled with newspaper, since this seems to make the colors shine a bit brighter (see figure 6).

Hutchens Copper Matt(from Gordon Hutchens)

Gerstley Borate...................... 80%Nepheline Syenite.................. 20

100%Add: Bone Ash...................... 20%

Cobalt Carbonate.......... 3%Copper Carbonate......... 7%

This glaze seems to produce the best results in terms of color density and brilliance if applied in a thin coat. I generally dab on two coats with a sponge or dip the piece once into a thin mixture (see figure 7).

SUCCESSFUL RAKU FIRING

Figure 1Shelf posts are located on the floor of the kiln. Place a post in front of the burner port with a corner facing the port.

Figure 2Place the shelf in the kiln. The bottom of the shelf should be elevated above the burner port.

Figure 3Place the pots on the shelf with about ½-inch clearance between each pot and the walls of the kiln. Place a Cone 07 as indicated and check the visibility of the cone with the lid in place before you light the burner.

Figure 4For a tightly sealed reduction can, bury the can in sand up to the rim. After placing a pot in the can, put the lid on, then scoop sand up to the rim to keep oxygen out.

George Juliano currently teaches ceramics at Robinson Secondary School in Fairfax, Virginia, and a graduate class at Virginia Commonwealth University, and his pottery has appeared in a number of regional shows. Send comments to gjuliano@erols.comElizabeth Hudgins is a retired English teacher and a published author of articles and poems. She is currently making her living as an iconographer of traditional Orthodox icons. Send comments to ehudgins@tidalwave. net

Pottery Making illustrated 15

SUCCESSFUL RAKU FIRING

Figure 5Vase, 12 inches in height, raku fired with Soldner Clear and reduced in trash can filled with newspapers to accentuate crackle in glaze.

Figure 6Vase, 14 inches in height, raku fired with Soldner Clear on top and Copper Luster applied thinly on bottom, reduced in trash can filled with newspapers

Figure 7Vase, 16 inches in height, glazed with Hutchens Copper Matt. The colors were achieved by immediately placing the fired pot in a sand-pit container and covering it, then quickly scooping sand around the lid edges to block the escaping smoke—thereby limiting the seepage of oxygen into the pit. After 10 minutes, I quickly removed the pot from the container and spray it with a fine mist of water to lock in the colors.

16 Fall 1998

by Sumi von Dassow

People new to glazing may be unsure whether they really want to mix up their own glazes, but they would like to experiment. Since the cost of an accu­rate gram scale can be an obstacle, an economical way to get started is with a volumetric recipe. Such a recipe requires the ingredients to be measured in cups (or teaspoons, tablespoons or buckets).While less exact than weighing ingredients to the tenth of a gram, this type of recipe can yield fine results and lends itself to experimentation.

A good place to start might be with the very basic recipe of 2 parts colemanite to 1 part Kona F-4 feldspar to 1 part silica. This becomes a clear glaze at Cone 5-6, but because of the high level of boron in the colemanite, it’s rather milky. It’s easy to add various coloring oxides or opacifiers in teaspoons and tablespoons to achieve a wide range of colors from this simple recipe.

Other experiments might be to substitute various feldspars for the Kona F-4, or to try simple additions of other common glaze ingredients. Keeping a supply of test tiles handy—or even pieces of broken bisque- ware—means that any time you get the urge to mix up a quick experimental glaze, you’ll have something to try it on.

Learning about glazes this way undoubtedly pro­duces in some strange results, as well as some success­ful surprises. As long as you keep good records, you’ll gradually add to your store of knowledge, and develop familiarity with the many glaze materials in a fun and nonstressful way.

While such experimentation isn’t likely to satisfy any potter forever, it offers an easy way to play with mixing and using glazes at home without requiring a large investment in equipment and materials or a great deal of space. Eventually, a gram scale will probably find its way into your studio, and you’ll be on your way to having a collection of 5-gallon buckets and filling the cupboards with raw materials.

Figure 1Test glazes, each consisting of 8 parts Sumi’s Volumetric Clear to 1 part Mason stain. Back row, left to right: stain 6319 (Lavender), 6364 (Tur­quoise) and 6387 (Mulberry). Front row, left to right: stain 6000 (Shell Pink), 6407 (Marigold), 6121 (Saturn Orange) and 6006 (Deep Crimson). Tests are on cones made from slabs rolled out on lace to show how the glaze looks on a textured surface.

Pottery' Making illustrated 17

Figure 2

Detail of carved orchid plate with Sumi’s Volumetric Clear Glaze mixed with commercial stain fired to Cone 6 oxidation.

Figure 3

Plate glazed with Sumi’s Volumetric Clear Glaze with commercial stain, fired to Cone 6 oxidation.

Mixing a GlazeA glaze screen, preferably

about 80 mesh, is an essential piece of equipment for straining wet glaze before use. It’s helpful to screen the glaze through a 40-mesh screen first to eliminate large lumps. You can purchase screens from pottery supply stores. You can also make one from window screen, though you won’t be able to get a fine mesh.

The easiest way to work the glaze through the screen is with your fingers, wearing rubber gloves. It’s also very helpful to dry-mix the ingredients, then wait at least a day after adding the water before stirring or screening the mixture.

CAUTION: When handling dry glaze ingredients, always wear a NIOSH-approved respirator. The fine powders create clouds of dust that are very bad for the lungs.

Volumetric RecipeThe following recipe was

developed from the basic recipe given (see story), and modified to reduce the milkiness and add the extra calcium required by many commercial stains.

The nice thing about this glaze recipe is that not only is it easy to mix, but with stains you can mix up several different colors of glaze, using only five basic ingredients.

The stains can also be mixed into the clay body or into engobes and painted onto the pot before bisque firing. This glaze can then be applied as a clear base. It can also be applied to a pot and decorated with stains mixed with a little glaze.

Sumi’s Volumetric Clear Glaze

(Cone 6)Colemanite.......................3 partsMagnesium Carbonate ....2Whiting............................. 1Kona F-4 feldspar............ 5Silica (Flint)...................... 3

14 partsAdd stain in amounts between

1 and 2 parts. The pink and red stains work nicely in a ratio of 8 parts base mix to 1 part stain. To test several colors, mix up a batch using large units such as cups.Mix the dry ingredients together thoroughly by shaking them in a large sealable bag or in a bucket with a tight lid; allow to settle before opening. Use 2 table­spoons of stain to each standard (8-ounce) cup of glaze mix.

Sumi von Dassow has been a potter for 18 years and currently teaches at Jefferson County Adult and Continuing Education in Golden, Colorado. Visit her website at www.well.com\~sumi

18 Fall 1998

ThrowingPhilosophy, Theory and Practice Pots

by Ivor Lewis

all pots are not necessarily big pots. Rather, they are forms that are several times higher than they are wide. Throwing high, slender, lightweight pots may seem an impossible task, but the secret of such an achievement is dependent on an understanding of the physical properties of the clay being used and an ability to plan a sequence of actions or activities that exploit this knowledge, followed by a willingness to practice and repeat them to obtain consistent results.

Each individual clay has a height limit beyond that it cannot be thrown or lifted, so special techniques are needed for the creation of very tall pots. This natural limit is a function of total mass, and the cohesion between particles of a clay/water system which govern its shear, compressive and tensile properties in response to force, often referred to as its “plasticity.” Plasticity is also related to the proportions of plastic and nonplastic constituents in the clay body.

Although some authorities advise the inclusion of coarser materials to aid the ability of clay to stand up, it’s the plastic components that provide the internal forces of cohesion and adhesion within clay/water systems that make this possible. Paradoxically, it would seem that when there is more plastic slippery material and less firm, solid, gritty stuff in a clay, then a potter has better chances of achieving tall pots.

This can be seen if the tall throwing sequence is used to take the clay to the limit. Beyond a certain point, a uniform thickness cannot be sustained from rim to foot. Stresses from gravity, torque and throwing friction prevent the clay from being lifted higher.Every clay has a limit beyond which it cannot be taken unless conditions are changed. Hence the use of burners, heaters or air drying between stages com­bined with coil and throw, part piecing and other techniques for creating very tall pots.

For anyone who has learned the elementary skills of centering and opening a ball of clay, the philosophy of the technique presented here is quite simple and based upon sound mechanical principles.The initial basic cylinder is treated as a series of sections, one above the other. The top, then upper sections, are thinned and pulled upward, using power transferred through stronger, thicker clay of the lower walls, that support the weight.

Understanding Your MaterialsYou can throw tall pots when you remember a

few things:• Once clay has been centered and opened into a

basic cylinder shape, it retains sufficient moisture to provide adequate lubrication for completion of the throwing and shaping of a pot.

• Some clays become more malleable, increasing in plasticity when pressure is applied, but return to a relatively rigid state when the deforming force is removed. This quality is called “thixotropy.”

• Thick clay is strong, needing more force to deform it than thin clay, which is weak and easily distorted.

• Adding grog or sand does not increase the strength of plastic clay and its ability to “stand up.”

• Beyond a certain point, the lower wall may twist if the upper portion of the cylinder is not worked first.

• Three or even four stages of preliminary thinning and lifting are needed to achieve a tall basic cylinder.

• Lubricating with excess amounts of water reduces the compressive strength of the clay.

• Increases in plasticity influence the structure, form and, more importantly, the height of the pot.The logic of these things isn’t hard to comprehend.

Thicker clay is better able to withstand the twisting stresses of throwing. Firmer clay stands up better under the action of gravity. Soft clay needs a light touch and a gentle hand because it provides its own lubrication. A good pot is thrown using conscious, reasoned decisions from the time the clay is weighed to wiring it from the bat when shaping and trimming are complete. Placement of the fingers, hands, arms and shoulders, and their movements, a balanced body position, control of wheel speed, even comfort and relaxation are all incorporated and integrated as part of a well-thought-out plan. Each attempt is a rehearsal which brings our attainment to perfection through closer approximations. Such slow learning and devel­opment eventually manifests itself as excellence in craft skills, which, when applied unconsciously, free our minds for creative thought.

Pottery Making illustrated 1 9

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Figure 1

Begin learning this new tech­nique with 4 to 6 pounds of clay.

As you make progress, use greater quantities. Don’t try to use a hard clay in the belief that it will stand up better or throw to a greater height than a softer clay. You’re learning and should not have to fight to keep the clay centered. Attempting to center hard plastic clay can also cause injury to your hands and wrists. As shown here, begin by centering and opening the ball of clay, using a style famil­iar to you.Your initial cylinder needs to be higher than it is wide, and the cavity should be as wide as your hand. When learning, height is more important than width or shape. Keep the bottom flat and make the indentation in the corner as small as possible (lA).The wall must be even in thickness from top to bottom. Take the usual precau­tions to prevent “S” cracks by compressing the base.

Figure 2

Avoid the usual step of making the next draw upward from the bottom of the pot. This requires a conscious decision. Instead, locate your fingers halfway up the inside of the pot (IB) and your right hand fingers opposite them outside. Set the wheel speed to ½ or less. Press your inner fingertips outward to make a groove. Clay has a couple of properties you’re about to exploit. First, it’s strong where thick, and weak where thin. Sec­ond, clay with optimum plasticity for throwing contains sufficient water and needs no extra lubrica­tion to ensure that it slides between your fingers. So, with the wheel spinning at between ½ and ½ speed, slowly pull the collar of clay upward, and reduce the wall thickness to half its original thick­ness. Leave the rim slightly thicker (2B) and let it run between your fingertips to remove any uneven­ness. The clay below where you have just thrown is thick, so it won’t buckle. The thinner clay at the top is still strong if you haven’t allowed water to soak into it from excessive lubrication. The clay you have just thrown is less likely to ripple or buckle because you have reduced leverage by shortening the distance through which your throwing force has acted.

Figure 3

Move your hands to the bottom of the pot (3A) and make a groove that undercuts the inside wall. Feel to get the same thickness (3C) as in the first stage. Give firm support on the outside to prevent the wall bulging outward. The clay will start to rise. There should still be suffi­cient slurry on the clay to provide good lubrication. Move your hands together, allowing the clay to extrude downward as you lift the wall upward with your fingers (3B), keeping the distance between your hands constant. If the clay starts to grab at your fingers, slow the wheel rather than adding more lubricant. Your hands should continue to move upward as one unit until they slide onto the thinner upper section (3D). Avoid any temptation to apply a squeeze at this stage. When you started this pull, energy was transmitted only a small distance through the weaker clay where it has been thinned below your fingers.

20 Fall 1998

Figure 4

In this figure you will see that the distance your hands move (4A) is small compared to the height of the pot, so leverage is reduced. Above the point where you slide onto the thin clay (4B), there is no need to apply strong force to extrude the clay.You only need that slight amount of pressure that is sufficient to true and collar the shape to the size you need. Again, at the top of this pull, firm and true the rim (4C).

At this stage, the preformed cylinder should be at least twice the height of that created on opening the clay.

Pottery Making illustrated

Figure 5

The advantages of working the upper portions of the pot should now become clear. The maximum twisting force is applied each time over only a small proportion of the full height of the cylinder; and the weight of clay that has already been thinned is supported by thicker, stronger clay. Furthermore, at no time does the full weight of the pot wall rest on clay that has been thinned except on completion of the final pull from the bottom. This factor becomes extremely impor­tant in the final stages of throwing. You should now be able to double the height of the cylinder and halve its wall thickness without changing its width. Though it would be possible to do this with a single pull from the bottom, recall that you’re learning a new and unfamiliar process. To revert to the popular style would introduce stresses in the weakest areas, a situation this method of throwing attempts to avoid. Instead, three separate stages are planned, work­ing first from the upper part (5A), then through the central section (5B) and finally thinning the lower part (5C).

Make a groove inside the cylinder (5D), then pull the clay up so that the outside of the wall remains concentric (5E). Again, use only the minimum amount of necessary lubrication. Provided you do not use excessive force, clay below the throwing point will not twist, shear, buckle, tear or collapse. Thick clay below where you’re throwing has all the strength needed to transmit the torque of the wheel at slow speed and support the weight of clay above. When you reach the top of the pull, true and firm the rim.

Figure 6

Move down to where the second stage of the lift will start and use your inner finger to make a groove (6A) as in the previous step. Firm support outside from your right-hand knuckle or fingers prevents clay bulging outward. Maintain this firm support as you lift and thin this section (6B). When you reach the thin section, relax your finger pressure and let your hands continue their upward movement.You should not thin this section even more, or there will be no clay to shape, an impor­tant consideration later when you’re creating new designs. Again, thick firm clay (6D) is giving support and transmitting power to the clay.

21

Figure 7

Now it becomes possible to see the advantages of this alternative method. This becomes clear if you imagine the cylinder in its inverted position, a situation illustrated in skeleton diagram (left 7) and the common result of always throwing from the base. Because the wall is very thin at the bottom (7A), that is where the clay is weakest.Yet this is the area of greatest stress when force is applied at the top of the pot (7B), to reduce the thickness of the firmer clay above. In addition, more stress is imposed by the effects of gravity from the mass of thicker clay. In contrast, by using this reversed style of throwing, the remaining thick clay collar at the base, which has yet to be thinned and pulled up, is still strong and firm. Making a groove for the next pull up (7C) imposes no strain on the weaker thin clay that has already been thrown. Take care to keep your forearm vertical as you make this final pull. Wetting your arm with slip prevents snagging, should you touch the wall or the rim. When your fingers slide onto the thinner clay (7D), relax the pressure between inner and outer hands and carry the pull up (7E) to the top with a light touch, then firm and true the rim. Because you are using only the minimum amount of lubrication necessary, water isn’t absorbed into the clay, which remains firm and capable of withstanding greater stresses coming from torque and gravity.

Figure 8

To complete the cylinder, keep the wheel turning slowly while you mop out the puddle that has collected in the bottom (8A). Use a flat rib (8B) to skim slurry from the outer wall. Trim the base with a slight undercut (8C) and refine the rim (8D).Your cylinder is ready for shaping. If your attempt has been successful, it may be preferable to cut under the base and set the cylinder aside to set up before inverting it for drying to finish.

Ivor Lewis is a retired teacher of Arts, Crafts and Science, but maintains an interest in ceramic production and research. Besides writing for Ceramics Monthly and Pottery Making Illus­trated, his articles relating to clay theory and practice are published in Australia and Ger­many. Ivor resides in Redhill, South Australia 5521, and can be contacted at 01-61-8-8636-7083.

Tip: Smooth slip, because of its beneficial physical properties, is a far better lubricant than plain water. It is by nature slippery.

22 Fall 1998

PORTA-KILNMARTHA PUCKETT'S

xcept for a few pots in the yard, the outside of Martha Pucketts house looks like the others in this older neighborhood on a tree-lined street in Louisville, Kentucky. Even the living room might fool you, and you might think she collects pots or even knows some potters. But if you get as far as the sun-room and see the dusty footprints, you know the neighbors just wouldn’t understand.

In the middle of the sun-room sits a potter’s wheel surrounded by boxes of clay. Nearby is a wedging board and shelves. All of it is overlaid with the clutter of partially finished porcelain pots, tools, notes and posters. In the large project room at the back of the house, she periodically makes reed handles for some of her work. To keep fumes out of the house, the electric kiln is in the garage.

Martha Puckett took all the ceramics classes that were available when she got her bachelor’s degree 30 years ago from Murray State University in Murray, Kentucky, but after graduation she did what was expected. She married and worked as an art teacher, and as happened to many women at that time, she was forced to quit when she became pregnant. Maternity leaves were unknown in 1970. Then, when her children were teenagers, she went back to teaching middle-school art.

As a graduate student in the 1980s, Martha attended a workshop presented by John Leach, and from seeing his individual work, became interested in the effects of smoke on pots fired in saggars filled with sawdust. After trying this technique, she soon started experimenting with other firing techniques that allow the smoke to mark the clay body. It was sawdust firing that really excited her, with surfaces as smooth as the wings of a butterfly, and the dark and light swirling patterns of smoke and fire left on the work. Soon, she learned to introduce colors to her work and found this gave her pots that seemed like a private universe.

Teapot, 9 inches in height. All functional pieces are glazed on the interior with Mayco C-300 Matt Transparent Glaze and fired to Cone 05 prior to the final sawdust firing in the porta-kiln.

Pottery Making illustrated

by Ginny Marsh

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The PotsMore intuitive than technical in approach, and with

limited space and resources, Martha learned to restrict her materials to those that were inexpensive and easy to acquire. Having found that a smooth white body best displays the luminous effects of the fire, she throws her work from a mixture of porcelain and white stoneware. The addition of the white stoneware makes a stronger pot, less prone to cracking from the shock of the sawdust firing. Martha uses 3 parts Standard Ceramics Porcelain Body 130 to 1 part Standard White Stoneware 182.

Finding that simple forms with wide smooth surface areas best display the effects of sawdust firing, she smooths off any unwanted marks with a used nylon stocking rolled up and stuffed into its toe to make a soft lump easily held in the hand.

After bisque firing the work to Cone 05, she applies Mayco C-300 Matte Transparent Glaze on the inside of utilitarian pieces, such as cups or teapots, and forms with rims that have been designed to be glazed.Glazed pieces are then fired to Cone 05 in an electric kiln prior to sawdust firing. The glaze develops a crackle pattern in the smoking process.

The KilnMartha usually prepares the work and materials

ahead and does the firing in the evening. She uses the following materials:1. One or more prepared pots (bisqued and glaze fired).2. A 3- to 5-gallon popcorn can with lid. Martha

prepares the can by punching or cutting about 30 holes into the can. The holes are from pencil diameter to nickel-sized, and they’re made with a large nail and a “church key.” Holes are located on the bottom and around the lower portion of the can to allow air intake so the combustible contents of the can will burn.

3. Two or three bricks, any kind. The bricks are placed under the can to promote air circulation and to keep the hot can off the ground.

4. Coarse, dry sawdust. Wood shavings leave too many air spaces and burn too quickly for adequate reduction and temperature gain, while very fine sawdust packs down, and leaves inadequate air spaces for sustained combustion.

5. Wood chips. Martha gets small kiln-dried scraps from a local cabinet factory.

6. A mixture of equal parts table salt and copper sulfate, perhaps 4 to 6 tablespoons per firing, if desired. Martha buys the impure copper sulfate sold in garden stores (used for controlling roots in drain pipes) instead of ceramic-grade copper sulfate. Table salt increases the tendency of the copper to volatilize.

7. Lighter fluid and lighter stick or torch.8. Fireplace poker or a ½- to ½-inch diameter steel

rod about 2 feet long.

The FiringMartha has a half-dozen cans of slightly different

sizes and with different configurations of holes in them; she fires one to six pots in each porta-kiln, and occasionally starts and tends up to three cans in one session. Her sawdust-firing process takes about two hours of active work and an additional three hours to allow the kiln to cool once the lid is placed on the can. She usually leaves her kiln to cool overnight.1. Choose a safe and adequate space on a ground

surface that will not burn. Martha likes to fire in an evening when there is no threat of inclement weather or wind.

2. Set the kiln on two or three bricks so the air can circulate under the kiln, and allow room to light the sawdust.

3. Fill the bottom of the can with 1 to 2 inches of coarse sawdust, pack the pots in the kiln, allowing at least an inch between them. Martha often places them upside down for the firing.

4. Sprinkle the mixture of copper sulfate and salt on the work.

5. Carefully cover the pot(s) with chips of wood at least 2 inches above the top of the largest pot.

6. Fill the rest of the can with more sawdust.7. After coating the top of the sawdust with charcoal

lighter fluid, use a torch (like the kind used for fireplaces or charcoal grills) and light the fire. CAUTION: Stand back and do not wear loose or synthetic clothing.

8. The porta-kiln should burn for an hour, more or less, according to the atmosphere, stirring the wood and adding more sawdust if necessary, until the pot can be seen glowing and the wood is burning well. This is more easily seen in the low light of evening than in midday sunshine. Martha lets the sawdust smoke heavily at stages, and at other times removes the lid to encourage a fierce flame.

Smoke from reduction forces black carbon deep into clay while hot spots develop where the wood burns away, leaving white patches.The fire in cans with the larger holes burns more quickly and intensely, leaving relatively larger white areas on the pots than on the pots fired in cans with smaller holes.

In the smoky reduction firing, copper typically turns red, but occasionally a flare in the firing leaves bright green traces. Combined with salt, copper sulfate is highly volatile and fumes at the low temperature of800°-900°C (1470°-1650°F), giving varied and unexpected color effects.

9. When the work can be seen glowing, place the lid on top leaving a 1-inch opening. The placement will have to be watched for a few minutes and adjusted so that smoke continues to come out the open area. The firing is essentially finished about an hour after the lid is put on the porta-kiln.

24 Fall 1998

Figure 1

A mixture of copper sulfate and salt is sprinkled over a pot nested in sawdust. Note that the bowl is placed upside down and is resting on coarse sawdust.

Figure 2Cover the uppermost pot with at least 2 inches of wood chips and coarse sawdust.

Figure 3Add lighter fluid and carefully light the kiln with a charcoal/ fireplace lighter.

Figure 4Allow the sawdust to burn for about an hour. If necessary, stir the wood and add more sawdust until the pot can be seen glowing and the wood is burning well. This is easily seen in the low light of evening.

Figure 5Martha places the lid on the kiln throughout the firing to reduce heavily, then removes the lid to encourage a fierce flame. During the second hour of the firing, she places the lid on the kiln and leaves a 1-inch gap to allow its remaining fuel to burn. Once the smoke ceases, the kiln is closed and allowed to cool slowly.

Pottery Making illustrated 25

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The ResultsBy the next morning, in the brief quiet before

work, Martha can remove the newly finished work from the cooled porta-kiln. The kiln often yields satisfying pots with a glimpse of a private world, but if she doesn’t like the results, she knows she can refire a piece up to 3 or 4 times without losing body strength.

Martha is always working on new variations on the shapes and firing technique. As you go out the door to the firing area in her small back yard, you may notice the small frame on the wall displaying an illustrated quote from William Blake’s Auguries of Innocence:

To see a World in a grain of sand,And a Heaven in a wildflower;Hold infinity in the palm of your hand,And eternity in an hour.

Or in a small pot . . .

TopPot, 4¾ inches in height, bisque fired to Cone 05 in an electric kiln, then sawdust fired in the porta-kiln, using copper sulfate and salt in a reduction atmosphere.CenterPot, 6½ inches in height. Martha Puckett restricts herself to small precise pots, usually less than 8 inches tall.BottomTeapot and cups. Teapot is 10 inches in height (including handle) and the cups are 2¾ inches in height.

Martha Puckett lives in Louisville, Kentucky. Scale, size and form are important considerations

for her and she is deliberate about restricting herself to small precise pots, usually less than 8 inches tall: “I want to create a simple elegant pot, which pulls the viewer in close to examine the beauty of its form and surface. Vm looking for pots that have two different aspects, elegant form and spontaneity created by the graphic markings of the fire. No two pots can or ever will be the same. I wonder if the first people who pulled a pot from the embers of the fire felt the same excitement. ”

Fall 199826

Pottery Making illustrated 27

28 Fall 1998

by Harold Hart

Glaze overlaps can extend a glaze library dramatically. Two glazes “a” and “b” become six glazes if you add the four overlaps: “a” over “b” (a/b) and its inverse (b/a), as well as self overlaps (a/a and b/b). Five glazes become 30 (5 glazes + 20 overlaps + 5 self overlaps), and the number of possibilities increases dramatically as you increase the number of glazes. But not all overlap possibilities work; some are ugly, some may crawl, and some may pit or do other horrible things, especially if applied too thickly.

I’ve worked mainly with tiles, but the methods described here can be applied to most thrown forms (bowls, cylinders, etc.) and even to handbuilt pieces. They can be especially useful for glazing like pieces (for example, a dinner set). I use a dipping technique for glaze application, but the overlapping ideas presented here may be used with pouring, spraying or brushing.

Note: I’ve not given the glaze names or recipes in the figures because it’s best if you work out your own overlaps, with your own glazes and firing conditions.

The ProblemConsider applying two glazes, “a” and “b.” One way to

do this is to use a standard overlap pattern illustrated in figure 1. Only two glaze sequences are possible:

Application Glaze Sequence1 a b2 b a

How can we make this boring way of using glaze overlaps more interesting? The trick is to devise applica­tion patterns so that 3,4 or even 5 glaze applications are possible, yet to never end up with more than two glaze thicknesses on any part of the piece, unless you have a special reason for wanting the glaze to be thick.

Pattern IIHere are a few application

patterns that provide the possibility to overlap glazes, which result in no more than two glaze thicknesses on any part of the piece. After exploring these patterns, you’ll surely be able to invent some for yourself.

Figure 2 illustrates a pattern you can use to apply single glaze thick­nesses (areas 1, 2 and 3) and three overlaps (areas 2/1, 3/2 and 3/1).

30 Fall 1998

Figure 1Depending on whether we apply glaze “a” or “b” first, the glaze pattern in the resulting piece will read, from left to right, either a, b/a, b or b, a/b, a. But that’s it, just two possibilities.

Figure 2

Using three single-thickness glaze applications in this pattern yields three single­glaze thicknesses (areas 1, 2 and 3) and three overlaps (areas 2/1, 3/2 and 3/1).

Basic Overlap Using 2 GlazesUsing the pattern shown in figure 2, you can take

two glazes, “a” and “b,” and apply them in such a way as to get 6 different sequences or results.The following chart shows the different possibilities.To use the chart, read it as follows: In glaze sequence “4, ” you would apply glaze “b” diagonally as shown in the first block in figure 2, then apply “b” again as shown in the second block. Finally, apply glaze “a” as shown in the third block. Figure 3 illustrates the result of each glaze sequence (not sequence 4 from the example above). Figure 4 shows glazed tiles using this pattern and the two glazes.

Application Glaze Sequence1 2 3 4 5 6

1 a a a b b b2 a b b b a a3 b a b a b a

Basic Overlap Using 3 GlazesIf we add a third glaze “ c w e obtain 24 different

possibilities! In addition to the 6 variations already shown (1-6) for glazes “a” and “ b t h e r e will be 6 analogous variations (7-12) for glazes “a” and “ c a n d another 6 (13-18) for glazes “b” and “c.” (You can work these out by substituting “c” for “b,” or “c” for “a” in sequences 1-6). Finally, there will be 6 more patterns (19-24) that use all three glazes a + b + c. These last 6 sequences are as follows:

Note:To the 24 we can also add 3 more—those that involve 3 applications of a single glaze: “a,” “b” or “c,” which give useful patterns of alternating single and double thicknesses of a single glaze around the piece.

Figure 4

Here is an example of 6 tiles using two glazes and the pattern shown in figure 2.

Figure 6This photo depicts 6 tiles glazed using the pattern shown in figure 2 using 3 glazes in sequences 19 through 24.

Application Glaze Sequence19 20 21 22 23 24

1 a a b b c c2 b c a c a b3 c b c a b a

Pottery Making illustrated 31

Figure 3

This diagram shows the 6 possible results using Pattern II and two glazes. Figure 5

This diagram shows the overlap patterns of 3 glazes applied in the basic pattern shown in figure 2 and in sequences 19 through 24.

Basic Pattern VariationTo illustrate how easy it is to

create patterns like this, figure 7 shows a variation on the basic pattern. Again, with 3 different glazes, 24 glaze sequences are possible. Figure 8 shows the last 6 of these, using application se­quences 19-24 (3 glazes).

Figure 8

Example of tiles glazed with 3 glazes using sequences 19 through 24 of this variation on the basic pattern.

Centrosymmetric and Dissymmetric Patterns

The basic pattern and its variation (figures 2 and 7) are centrosymmetric, but off-center (dissymmetric) patterns can add to the interest. Figure 9 shows round tiles glazed with identical application sequences, but with centrosymmetric and dissymmetric patterns, respectively:

Figure 9Example showing pieces may be glazed centrosymmetrically (top) and dissymmetrically (bottom).

Figure 10

The tile at the left in each series was glazed with a single glaze “a”; the next two were glazed with 2 glazes “b” and “a,” applied according to the sequences “a,” “a,” “b” and “a,” “b,” “b” respectively.

32 Fall 1998

Figure 7

Variations on the basic pattern are simple to create.

Advanced PatternsThe more applications, the greater the number of

possible glazing sequences. Lets see how we can jazz up the simple overlap of the pattern shown in figure 1 by adding two more applications (see figure 11).

There are 81 different glaze sequences for this 4- application pattern, using only 1, 2 or 3 glazes! A simple formula can give you the number of possibili­ties.

[no. of applications][no. of glazes] =[no. of sequences]

In this case, there are glazes and 4 applications or3 , which equals 81 sequences (3x3x3x3=81).

I show here only 12 such sequences, obtained from2 applications of glaze “a” and one each for glazes “b” and “c”:Application Glaze Sequence

1 2 3 4 5 6 7 8 9 10 11 121 a a a a a a b b b c c c2 a a b b c c a a c a a b3 b c a c a b a c a a b a4 c b c a b a c a a b a a

Figure 11

There are two variables in the number of possible glaze overlap sequences—the number of glazes available and the number of applications made. Here is a pattern showing how to make 4 applications where no part is greater than 2 glazes thick.

Figure 13

Every piece will be different, yet their glazes will be similar. Here are four juice glasses glazed with the same three glazes. Each glass is unique, yet works well as part of a set.

Theory into PracticeIf you have a number of similar pieces to glaze (bowls, plates, mugs, etc.), you can glaze them similarly yet differently by using a glaze overlap sequence. Here’s a method I’ve used.

1. Set out 3containers (or 2, if you plan to use only 2 glazes), each containing a different prepared glaze (sieved, stirred, etc.).

2. Following the particular application pattern you have selected or designed, make the first application to each piece. For example, if you were to use the 4-application pattern shown in figure 11 with (2a + b + c) glazes and 12 pieces, you would apply glaze “a” to the first 6 pieces, glaze “b” to the next 3 pieces and glaze “c” to the last 3 pieces, going across the first line of the glaze sequence table shown.

3. Make the second application across the table, and so on. It’s faster doing it this way than vertically down each column of the table, because glaze is applied to each piece in the same way.

4. Allow time for drying between applications.5. The lines in all the patterns shown are straight, but this

does not have to be so, especially if a different method of glaze application is used, such as pouring or spraying. There is loads of room for irregular patterns and for exploration.

Figure 12

Shows 6 tiles, each glazed with the same 3 glazes, but applied according to sequences 7-12 in the table (you can work backwards from the tiles and table to deduce that glaze “a” is lavender, “b” is gold, and “c” is green). Harold Hart is Professor Emeritus of Organic

Chemistry at Michigan State University. He has no training in art, but began pottery classes in 1977 at the Greater Lansing Potters'Guild, Michigan, and became a guild member in 1980. Send comments to Mr. Hart at PO Box 321, Okemos, Michigan 48805-0321.

Pottery Making illustrated 33

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Tile setters provide a way to make efficient use of a kiln

by Barbara CoultryI decided (innocently) to make my own tile setters, so I looked

around for inspiration. I discovered those Styrofoam® corners used in packing, and ended up with a tile setter system that I love and often employ for objects other than tiles. Here’s how I made my own setters.

Procedure1. Roll a ¾6- to ½-inch slab of grogged high-fire clay.

Use clay suited to your firing range. This means employing clay rated several cones higher than you’ll be using for your ware, which guards against serious warping. For instance, my tiles are made from low-fire earthenware, so I use Cone 6-8 grogged stoneware for my tile setters. (I must admit to some warpage, but this occurred when I rested items on the very edges of the triangular top pieces.)

2. Using a ruler or cardboard template, cut out the pieces (see figure 1). Allow the pieces to dry about halfway to leather hard so they don’t collapse during the construction.

3. I use a small scrap of pine board with a standard ¾- inch thickness as a form around which to mold each setter. Making sure it had one good right angle, I sanded it just enough to remove the gross roughness. Using the block assures me that the two triangular pieces will be parallel to each other.

4. Score the triangles and strips where indicated by shading in figure 1. Apply slip to the strip, place a ¾-inch thick wood block on it, adhere one edge of each of the two triangles, then wrap the strip around, adhering it to the second side of each triangle as indicated in figure 2.

5. When you have finished constructing the setters, cover them with plastic and allow them to dry slowly.

6. If you don’t have one, get a drywall sanding sheet, a wire screen with embedded grit, from any hardware store. When the setters have completely dried, use the drywall sanding sheet in a circular motion to level and smooth the tops and bottoms, thus elimi­nating any dangerous tendency to wobble. (Tip: It also does a lovely job on the bases of pots, cups, bowls, etc.)

7. Fire the setters before using them. Green clay moves about much more than bisque does in the heating and cooling process. Don’t risk ruining your work by having it topple off a fluctuating support. Fire your setters close to the clay’s upper temperature range; for example, fire a Cone 6-8 stoneware body to Cone 8.

34 Fall 1998

TILE SETTERS

Pottery Making illustrated

Figure 1

From a 3/ie- to 1/4-inch thick slab of clay, cut out setter parts as indicated. Remember you’ll need two triangles for each rectangular strip. The width of the strip is ¾ inch plus twice the thickness of the slab. Make cardboard templates to speed the process.

Figure 2

Attach the 2 triangles to the rectangular strip, using a ¾-inch-thick sanded wood block (not shown) as a guide. Bend the rectangular strip into place and attach with slip.

Barbara Coultry, a frequent contributor to PMI, resides in East Greenbush, New York, where she owns and operates Coultry Pottery.

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36 Fall 1998

Slab Potteryby Norman Holen

A series is a group of vessels that relate to each other through a concept. Whenever I begin a new series of pots, the decision involves what I want to include as well as what I wish to exclude. For a recent series, I decided to choose the slab method over the wheel- thrown pot, setting aside fully rounded shapes in favor of pieces with major front and back views and two narrower side views. I also wanted to add decorative elements to the sides to accentuate the design, as well as transform the conventional foot into a base to attach the pot and secure the side shapes. Here’s how I developed the series from concept through completion.

It’s always exciting working with a new series. As I continue to create these pots, one piece just naturally leads to the next.

Figure 3

I place my drawing on the clay and transfer the image by pressing down on the fettling knife while following the lines. This process leaves an indented track in the clay, that I follow when I cut out the clay pattern.

Figure 1

I start with a drawing, because various alterations can be made with an eraser prior to the building process. In fact, several versions can easily be drawn and the best ones selected.

Figure 2Place the clay on a piece of canvas between two guides, lengths of lath slightly less than ¾-inch thick, then flatten it with a rolling pin. To keep the clay from sticking to the rolling pin, place a half page of a newspaper on the clay before rolling. The paper needs to be replaced frequently to keep it from deteriorating, but the rolling pin stays dry.

Tip: A side light (rather than direct overhead lighting) can be used to see the indentations more clearly.

Pottery Making illustrated 37

Figure 4I add about 3/ie inch to each side of the body of the piece to compensate for the narrowing of the width as I curve the slab of clay.

Figure 5I score and attach each half to an oversized slab base, which I leave untrimmed until later. The delayed decision will allow for deviations from the drawing that may occur as the pot develops.

Figure 6

I trim the pot after the full height has been achieved and before the side pieces are attached in order to have the greatest access to all surfaces.

Figure 7

After the “wings” are finished, I trim the base with a slight bevel. I bisque fire the piece, then glaze and refire it to Cone 6 in an electric kiln.

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38 Fall 1998

Figure 8

The finished vase measures 101/s inches high by 7Va inches wide and 2¾ inches deep.

Horizontal vase, 71/4 inches high by 13 inches wide and 3¾ inches in depth, slab built, decorative elements have been added to the sides to accentuate the design.

Pottery Making illustrated 39

Professor Norman Holen has been teaching at Augsburg College in Minneapolis, Minnesota, since 1964.

PHOTO: ILENE HOLEN

Pottery Making illustrated 41

by Craig Hinshaw

Figurative ceramic sculpture has a rich tradition. From China’s ancient life-size ceramic army toViola Frey’s contemporary grandmother figures, artists select clay as a means for expressing the human figure. I’ve found elementary-grade children just as enthusiastic about shaping figura­tive sculptures, although on a smaller scale, as ceramics artists from the past to the present.

Children are always excited to work with clay. When we are going to make figurative sculptures, I chan­nel their energy into the lesson by having them become living sculp­tures. I ask the students to pose as a figure they might be interested in shaping in clay. I also encourage the students to consider making a self- portrait by asking what they enjoy doing: Playing baseball? Reading? Playing with a pet? Once the stu­dents have “struck a pose,” I ask them to notice how their body, elbows and knees are positioned. Throughout the lesson, they may need to become a living sculpture again to solve problems they’re having with making their sculpture look right.

As a closure, I ask the students to once again become a living sculp­ture, allowing them to judge for themselves how successful their fin­ished piece is. But it is obvious to me how they feel about their work. The students’pride shows in the way they carefully wrap the little sculpture with tissue and tape to protect it on the way home to show their parents.

Finished sculpture of cheerleader (shown in figure 1), approximately 4 inches in height.

Many of the boys in this third-grade class had just signed up for little league baseball and chose that idea for their sculptures. This batter has just made contact with the ball.

To stimulate the students’ imagination, I ask, “What pose would your mother recognize you in?” This was the pose a third-grade girl chose for her self-portrait.

This girl’s best friend had moved to another city. When she went to visit her, they walked to a park and sat on a large, half-buried tractor tire to share time and memories together.

42 Fall 1998

Figure 1

I demonstrate one method of creating a figure from clay. Starting with a 1-pound ball of clay, I pinch out the head, arms and legs, then begin manipulating my little figure into the desired pose.Another method many students choose is to first make the individual body parts—body, head, arms and legs—then connect them. Here, a second-grade girl works on her cheerleader sculpture.

Figure 2

If students want their figure to stand, they must construct the legs fatter than normal to support the weight of the clay, as this second-grade girl has done. The figure should be attached to a clay base, but if the sculpture still wants to fall over, extra clay should be shaped into a temporary support to hold the piece upright until it dries, then the support can be removed.

Figure 3

Working on a small scale dries the clay out quickly; small amounts of water may be needed to connect pieces and smooth cracks. Toothpicks are used for finishing touches—adding eyes, mouth and defining clothing—as demonstrated by this second-grade boy. Young students often represent a nose with a hole made by the toothpick. I show them how a more realistic nose can be shaped using a very small piece of clay and carefully smoothing it in place using the toothpick. When completed, the little sculptures are allowed to dry for a week and then bisque fired.

Craig Hinshaw is an elementary art specialist in the Lamphere School District in Madison Heights, Michigan. Send comments to hinshawc@lessenger. lamphere. k\2. mi. us

Figure 4Although glazes can be used to finish the pieces, I prefer watercolor paints, which give the clay a nice soft-looking patina. When the watercolor dries in a matter of minutes, the students paint over the entire sculpture with acrylic polymer, which I’ve diluted with water, about 50%. The polymer gives a clear glazelike sheen while also helping adhere delicate parts.

Note: White glue works well for reattaching broken parts.

Pottery Making illustrated 43

Looking fora white glaze in the Cone 4-6 range? Per­haps one of these will do. Try a test batch first before applying to your ware.

White Glaze(Cone 4-6)

Dolomite.............................. 13%Wollastonite........................ 22Nepheline Syenite.............. 43Kaolin................................ . 22

100%Add: Zinc Oxide.................. 3%

OfF-White Stain Matt Glaze(Cone 5-6)

Barium Carbonate.............. 5%Whiting................................ 19Custer Feldspar.................. 54Kaolin................................. 16Flint..................................... 6

100%Add: Zinc Oxide.................. 9%

Rutile (milled)............ 5%Also try this without the rutile.

White Glaze with Markings(Cone 5-6)

Cryolite............................... 8%Lithium Carbonate.............. 8Whiting............................... 7Kaolin................................. 30Flint................................... . 47

100%Add: Titanium Dioxide........ 13%

Zinc Oxide................. 34%

White Matt Glaze(Cone 5-6)

Lithium Carbonate.............. 12%Whiting............................... 5Kaolin................................. 28Flint................................... . 55

100%Add: Titanium Dioxide........ 8%

Zinc Oxide................. 25%Note: Test all recipes before use. Materials, firing conditions and clay bodies vary from studio to studio.

44 Fall 1998

The Glaze Room

y son was in his mystical phase. He had astrol­ogy charts and tarot cards and piles of books on various sorts of arcana. And he wanted a set of rune stones. Not just any old set, mind you, but a personal set, one made exclusively for him. Well, you know who offered to fulfill his wish.

Many molds and stamps later, I had three sets of bisqued “stones.” I dunked them in little glaze jars by designing equally little dipping tongs (see PMI,Winter 1998, “Closet Tongs”).

At the time I had 75 “stones,” but only 23 three­pronged stilts to support them. Well, I thought, I have 17-gauge high-fire wire and I have clay. What more do I need? As it turned out, nothing. Three sets of rune stones came through the glaze firing just fine on homemade stilts, and my son picked the set he liked best, and marked the others for sale (he the entrepre­neur, I the willing fool).A Few Rules

There are a few rules for making your own stilts and props, most of them applying to wire. After testing, I’ve concluded that you should use nothing but metal specifically designed for kilns. Steel nails and screws can withstand fairly high temperatures, but they develop a fire scale that flies off and embeds itself in glazes as the kiln cools.

Nichrome wire is rated for Cone 5 (2230°F). Composed of 80% nickel and 20% chromium, it will resist oxidation up to 2200°F and won’t melt until it reaches 2550°F. Kanthal wire is used for kiln elements, and for the pins and staples that secure these elements to the walls. It’s rated for approximately 2400°F.

The gauges commonly found are 9, 15, 17 and 24. Don’t use the 24 gauge. It’s appropriately called “stamen wire” and is far too thin to support much more than a flea. I believe element pins and staples are 17 gauge, and they’re wonderful sources for a truly high-firing wire. And don’t use coiled element wire— it’s too curly.

Figure 1When producing a 3-pronged triangular stilt, wires should be approximately double the depth of the clay.

Pottery Making illustrated

Match the wire’s diameter to the weight you want to support. After losing part of a kiln load to just such a miscalculation, I now deliberately overestimate the necessary strength.The lightest wire I’m willing to use is 17 gauge, and then only for small stilts supporting items no more than the size and heft of teacups. If you want to support larger items, use 15 gauge.

I’ve used both 17 and 15 gauge for beads, my experience suggesting 17-gauge wire as the choice for jewelry beads since you don’t want the holes too large. However, keep the wires short, no more than 3 inches, to guard against the wire sagging from the heat.You have less to worry about using 15-gauge wire and can extend the length to 5 or 6 inches, depending on the size of the bead.

Here are a few very basic designs for props. Use them and anything you find as a jumping-off place. Just because you’ve never seen it before doesn’t mean that your individual design or need isn’t valid.

You will want a pair of wire nippers capable of cutting fairly heavy wire. Tip: If you have a good pair of nippers, but need more leverage for cutting heavy wire, scrounge up two pieces of copper plumbing pipe and fit one over each handle. It will give you the added length necessary for extra leverage.

Measure the pieces of wire carefully. Machine precision isn’t possible, but you can get close enough so that, with a gentle bend here or there, you can have confidence that your work will remain where you placed it.

When firing big, heavy items, I use clay “points”(see figure 2). Points contain no wire and they are the one and only stilts for which I recommend making a mold, since they all need to be the same height. Fashion a prototype, make a plaster mold of it, then crank them out.

Mby Barbara Coultry

prop itUP

Figure 2

prop it

Figure 3I created the “noodlehead” by attaching narrow tubes of clay to a slab base. The noodlehead holds, suspends and supports items for which there seems no other solution. It has propped up porcelain flowers that ended in tubes awaiting wires, held makeshift bead bars, supported lids and bowls, and served as a mutable stilt with the addition of high- fire wires placed strategically in the tubes.

ClayUse clay suited to your firing temperatures (see

box).This means employing clay that is rated several cones higher than you’ll be using for your ware, which guards against serious warping of your stilts and supports. Grogged clay is better for large supports; it hardly matters for small ones.

To eliminate any dangerous tendency to wobble, rub the bottoms of unfired pins and props with a circular motion across a drywall sanding sheet to level the base. Drywall sanding sheets are wire screen with embedded grit, and they’re available from any hard­ware store. Tip: Drywall sanding sheets also do a lovely job on the bases of pots, cups, bowls, etc.

Figure 4The variety of designs is derived from what is needed.

Small Stilts Step-by-Step1. Roll a slab of clay ¼- to ½-inch thick. Punch or

cut out your chosen shapes (triangle, circle, oval, bar, etc.). Producing curved shapes is easier if you cut a strip of metal from a tin can, form it into the shape you want, and use it as a cookie cutter. Since your stilts will shrink in the first firing, make them a little larger than you want the final product.

2. Snip as many support wires as you’ll need.The length of the wires should be approximately double the depth of your clay (for example, for a ¼-inch slab, you’ll need ½-inch wires).

3. With the clay shapes lying on a flat surface, push the wires down through the clay until they hit the underlying flat surface.

4. Once they’ve been fired, you may find you have to occassionally bend a wire to even out the heights.As long as it’s only a slight bend, it’ll work fine. If you need to bend the wire much more than 10 degrees, nip off a tiny bit of it instead. The straighter the wire stands, the more weight it can support.

Multirange Stilt BodyBall Clay.............................. 78%Georgia Kaolin (ASP 400) . 10Flint................................... 12

100%This recipe should provide high-quality stilts when the forms are press molded and bisque fired in the stoneware range.

SOURCE: Answers to Potters’ Questions, 1990. The American Ceramic Society.

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47Pottery Making illustrated

48 Fall 1998