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Docent English CourseElenor Wilson, Instructor

June 4th, 2011

SURFACE & FIRING

A VERY Short History:

The Greeks were the first burnish clay surfaces to achieve agloss-like finish and make it water-tight. They also inventedsigillata which is a very fine slip applied to the outside of a clay potbefore firing to create a satin-like smooth finish. The use of high-silica content material for ceramics dates back about 5,000 yearsto Egypt and Syria. Lead, a low-melting-temperature material wasintroduced to glaze materials about 3000-2500 B.C. In 1500 B.C.kilns were developed in China that could fire to much highertemperatures. This in combination with the availability of

stoneware allowed the Chinese to develop higher temperatureceramics and glazes. They continued to lead the world in clay andglaze development, and during the Song Dynasty, 960-1220 A.D.

porcelain wares were developed. Jumping a long way forward intime to the late 19th century, a German man named Dr. Segerdeveloped what we now use as modern glaze formula andcalculation based on theperiodic table of elements, eutecticsand other physics and chemistry stuff. Here is a contemporarysample glaze formula:

Basic Celadon (Chn) Glaze

Feldspar (high-silica clay) 37Kaolin (China Clay) 18Silica (glass) 28Calcium Carbonate (CaCO3) 12Dolomite (CaCO3 MgCO3) 03Bone Ash (3CaO P2O3) 02

(100)Iron Oxide (FeO2) + 1.5% or less

Typical Stages of Clay to Ceramic firing:

1

Greenware: unfiredclay

wet=malleablebone dry = no

Bisque ware: oncefired clay, willabsorb water/glaze

Glaze ware:ceramics with anouter coating ofglass, usually to

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Glaze/Surface Application Techniques

NAME DESCRIPTION STAGE OTHER

1 brushing

applying glaze orslip in a traditionalpainting manner

with a brush

slip greenglaze bisque

2 dipping

quickly applyingglaze by dipping

the piece in alarge vat of glaze

bisque

3 sprayingusing compressed

air and a spraygun to apply glaze

green or bisquecan achieve a

very thin layer

4 pouring

holding the objectwhile pouring a

glaze over all orpart of it

bisque

5 sponging

using a sponge tostipple slip orglaze onto the

surface

green or bisque

can get an evencoating by hand

or add visualdepth withdifferent

glazes/colors

6 trailing

use a squeeze-bottle to draw thin

lines of slip orglaze onto the

surface

green or bisque

7 sgraffito

covering thesurface with a

colored slip, thencarving away to

reveal acontrasting color

or texture

green (typically) nice for graphics

8 wax resist

using hot or cold

wax to stop glazefrom going ontothe surface

bisque

9 intaglio

carving into thesurface then filling

the carved lineswith color

green or bisque

10

luster/overglaze

applying a metallicor color enamel on

top of the glaze

surface

glazeware

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More Descriptive Vocabulary:

matte dull, not shiny, textured surface, opaque

satin a little shiny, smooth surface, opaque

gloss very shiny, reflective, very smooth transparent

crystalline crystals form in the glass during cooling; some produce

colors

transparent can see through, like glass

translucent light can pass through, or illuminate, but it is not

clear; you cannot see through

opaque the opposite of transparent and translucent

colorant a chemical or combination of chemicals added to a glaze

to produce a color

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Kiln & Firing Vocabulary:

low temperature up to 1100 Centigrade (Celsius)

mid-range temperature up to 1220 Centigrade (Celsius)

high temperature around 1300 Centigrade (Celsius) and higher

electric kiln uses electricity to heat a metal coil, oxidationatmosphoere

gas kiln burns propane or natural gas to heat the kiln, typically

reduction atmosphere; can produce beautiful richcolors; celadon and copper- red glazes are produced this way

oxidation lots of oxygen in the kiln

reduction almost no oxygen in the kiln

wood-fire kiln (i.e. Anagama) wood is the fuel used to heat the

kiln; wood ash combines with the silica inthe clay to produce a glaze on the surfaceof the pot; flames leave their print on thesurface as well.

Raku kiln/firing low temperature firing in which the molten pot isremoved from the heat, put in wood fiber to create ametallic surface through a reduction burn, then cooledquickly in water.

pit firing low-temperature firing in a hole in the ground, usuallygives a smoky or black patterned surface

salt firing salt (NaCl) is put into a gas-firing kiln at 1060C or aboveto create a glazed surface by combining with thesilica in the clay

soda firing Sodium Carbonate (NaCO3) is put into a gas-firing kilnat 1060C or above to create a glazed surface bycombining with the silica in the clay; many artists/pottersuse applied glaze in addition to the sodium carbonate to

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create a variety of colors and surface textures

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