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Heating stone changes them to a moreGlassy medium and eases the job of Knapping and flaking tools and spearpoints. It also Enhances the color on some stones.

Heating Gem stones clarifies and changesThe color to make them more desirable byThe cave girls.

First a little

History………

Paleolithic Period (Stone Age) 2.5 million years ago – about 10,000 BCUse of fire, Stone Tools.

Lower Paleolithic – Neanderthal Middle Paleolithic - Cro-Magnon 40,000 years ago

Upper Paleolithic – 30,000 – 10,000 BC

Middle Paleolithic - Cro-Magnon 40,000 years agoUpper Paleolithic – 30,000 – 10,000 BC

Cave Art from The Cave of Chauvet-Pont-d’Arc France

Appx. 31,000 years ago

Upper Paleolithic 30,000 – 10,000 years ago

Neolithic (New Stone Age) 10,000 years ago to 2,700 BC

Beginning of Agricultural society, Villages, Pottery makingAnd Ovens & Kilns.

Heating of Cherts, Jaspers, & other stones for tool making Early metal work, Art. Stone Working progressed to an art.

Sphinx 2723 – 2563 BC

Current Era 2700 BC to Today

Pliny, (23 to 79 AD)

“To tell the truth, there is no fraud or deceit in the world which yields greater gain and profit than that of counterfeiting gems.” -History of the World

Tribal witch doctors, seers, and sages, and flourished during the Neolithic era and were the precursors of Alchemists studying the transmutation of

stone and metals from one form unto another.

Today they are known as doctors and scientists.

Current Era 2700 BC to Today

From 2 Egyptian papyri 3rd or 4th century

False Ruby“Take smoky crystal and make the ordinary stone from it: Take and heat it gradually in the dark; and indeed until it appears to you to have the heat within it. Heat it once more in gold-founder's waste. Take and dip the stone in cedar oil mixed with natural sulfur and leave it in the dye, for the purpose of absorption, until morning.

Corroding and Opening Up of Stones“Grind alum and melt it carefully in vinegar. Put the stones therein, boil it up, and leave them there over night. Rinse them off, however, on the following day andcolor them as you wish by use of the recipes for coloring.

Current Era 2700 BC to Today

Teifaschi, in his treatise on gems from about 1240 AD, had this to say:

In Sarandib [Sri Lanka] and its environs, ruby is treated by fire. People take pebbles from the earth and crush and compress them into a mass with the aid of water. [This mixture] is daubed completely around a dry stone. Then, the whole thing is placed on a rock with other rocks set down around it. Dry firewood is thrown on top, lit and blown upon [with bellows]. The blowing is applied, along with more wood, till any black overtones on the ruby have disappeared.The ruby is not heat treated a second time. After one treatment, its color can neither improve nor diminish.

Current Era 2700 BC to Today

Natural Magic, John Baptist Porta, Naples[ca. 1535–1615]

For example, we would have a Sapphire should be white on one side,and blue on the other; or should be white on one side, and red on the other: thus it may be done. Plaster up that side which you would havered or blue, with chalk, and let it be dried; then commit it to the fire, those ways we spoke of before, and the naked side will lose the color and turn white, that it will seem a miracle of Nature, to those that know not by how slight an art it may be done.

Current Era 2700 BC to Today

1850’s Sri Lanka people coated Ruby rough with lime and Betel

Leaves, then cooked in hot fire until the blue tinge was gone.

Early 1900’s Sri-Lank Ian's began heat treating Geuda (poor quality)

Sapphire to obtain the brilliant blue, and get rid of the ‘silk’ (rutile Strands).

1920’s – 1950’s High Temperature ovens became in use & Professor

and Madame Bron of Company Grasset and Bron, rue Chantepoulet,Geneva Developed the modern Method of heat treating Ruby and produced

the ‘Geneva Ruby’, a a forerunner of Verneuil synthetic Corundum.

Modern By the latter part of the 70’s, large numbers of

heat-treated Sri Lankan sapphires were streaming out of Thai ovens. In the early days of what amounted to the Great Geuda Rush, rough

could be had for a song and fortunes were amassed overnight. The rest, as they say, is history…

BEFORE

AFTER

The Mong Hsu ruby is almost always an ugly duckling. There are twomajor problems. The first is dense silk/particle clouds and a strong

purplish color, making most stones look like low-grade, cloudy rhodolite garnet.

This is mainly due to the crystal’s unusual blue cores. Ordinary heat-treatment removes the blue, as well as removing silk,

making the final product a rich, clear red.

Gemstones & Their Treatment Types

Alexendrite: None Amethyst: Heat Treatment Aquamarine: Heat Treatment Coral: Dyeing Druzy Quartz: Dyeing, Heat Treatment, Irradiation, Vapor Deposition Citrine: Heat Treatment Diamond: Irradiation, Lasering Emerald: Filling, Impregnation, Waxing/Oiling Garnet: None Lapis Lazuli: Dyeing Onyx: Dyeing Opal: Filling, Impregnation, Waxing/Oiling Morganite: Irradiation Pearls: Bleaching, Dyeing, Irradiation Peridot: Impregnation, Waxing Rubelite: Heat Treatment Ruby: Heat Treatment, Flux healing, Fracture Filling Sapphire: Heat Treatment, Flux healing, , Fracture Filling, Lattice Diffusion Spinel: None Tanzanite: Heat Treatment Topaz: Heat Treatment, Irradiation Tourmaline: Heat Treatment, Irradiation Zircon: Heat Treatment

Most gemstones, with the notable exception of garnet, have a particular treatment, or series of treatments that are commonly used to increase the marketability of the stone.

Ways to Heat Treat Rocks

• Aboriginal or Fire Pit• Barbeque or Washtub• Kitchen Oven• Countertop Roasting Pan• Kiln• Special high degree heating Furnace for

gemstones

Ways to Heat Treat Rocks

Abo or Fire Pit

1. Dig Pit2. Bed of Sand3. Layer of rock4. Sand/dirt on top *5. Build fire6. Tend for 2-3 days7. Let cool8. Remove rock

*Sand or dirt cover should beat least 1”. Temp will decreaseAbout 50 Deg. Per additional ½ inch. Heat is from the top.

Ways to Heat Treat Rocks

Barbecue or Washtub Method

Basically the same as the Fire Pit only using a barbecue Or a washtub and CharcoalAs the fire.

Use enough charcoal to coverThe sand completely and addMore as needed for a couple Of days until done.Heat is from the top

Abo or Fire PitDisadvantages

1. Dig pit2. Enough wood/charcoal3. Tend fire for long periods4. May have to re-do a couple of times5. Makes a hole in the yard6. Hard to tell temperature7. Hard to maintain temperature8. Charcoal can be expensive

Advantages

1. Gives you the satisfaction of doing it the primitive way

Ways to Heat Treat Rocks

Oven Method

Use a Roasting pan that is atLeast 4” deep.

Put about 1” sand in bottomLayer in RockPut about 1” sand on topCook for desired time Let Cool(can be smelly)

Oven MethodDisadvantages

1. Ties up the oven for a couple of days2. Heats up the house in the Summer3. Can get real smelly from oil evaporating from rocks4. Electricity/gas to run oven can be expensive

Advantages

1. Even heat source2. Maintain proper temperatures3. Less tending4. Less likely to have to re-do

Ways to Heat Treat RocksRoaster Oven

1. Remove inner pan and rack2. About 1” sand in bottom3. Layer rock4. ½” Sand5. More rock etc….6. Top layer of sand about 1”7. Cook for desired time8. Let cool 9. Remove sand & rock

Roaster ovens can be purchased new for $45 and up depending on the Brand and the temperature they go to. I bought mine used from GoodwillFor $15. The roaster oven needs to be able to go to 500 degrees.

Roaster OvenDisadvantages

1. Heat is hotter in corners and on the bottom layer2. Cost of oven if purchased new3. Cost of electricity

Advantages

1. Can be used in garage or carport and not smell or heat up the house2. Fairly even heat3. Can be stored when not using it4. Can clean it and cook the Thanksgiving Turkey 5. Is fairly economical 6. Heat treat a good amount and variety of material at once7. Less tending needed

Ways to Heat Treat RocksKiln

1. About 1” sand in bottom2. Layer rock3. ½” Sand4. More rock etc….5. Top layer of sand about 1”6. Program cooking times7. Let cool 8. Remove sand & rock

These are special made kilns for rock cooking. They are completelyProgrammable and are made by a pottery kiln company. For moreInformation http://www.thenaturalearth.com/kiln.htm. Cost is$685.00 plus shipping.

KilnDisadvantages

1. Cost2. Weight3. Specialized equipment

Advantages

1. Exact temperature control2. Programmable ramp, hold, & cooling 3. Virtually no tending from start to finish4. More predictable results5. Will contain odors

How its Done !• Prepare rock so that you have slabs or in the case of flints & cherts

Make your bifaced blanks.

• Thickness matters, try to use pieces of the same thickness

• Over ½” pieces take too long to heat

• Place thicker pieces on bottom or if you are doing various typesof rock, put the ones requiring the most heat closest to the source.

• Some people use Vermiculite instead of Sand

• Abo/pit style the heat is at the top

• Oven/kiln heat is surrounded

• Roaster heat is mostly on bottom

Heating PhasesPhase 1. Drying the rock

Bring temperature up to 150 – 250 degrees and cook for 4 – 8 hours

Phase 2. Ramp up temperature

Begin raising temperature by 50 or 100 degrees per hour to the desiredTemperature. (depends on the type of rock)

Phase 3. Hold temperature

Hold the temperature at the desired maximum for anywhere from 0 minutes to 30 hours depending on the type of rock.

Phase 4. Reduce temperature

Reduce temperature by 50-100 degrees per hour to about 125 degreesThen you can shut off your oven-roaster-kiln and let finish cooling

Rock RecipesThe ramp times, temperatures, & holding times vary dependingOn what you read. But generally they are as below. (From severalKnapping Sites, Holding times may need to be longer for Lapidary)

Montana Agate 450 - 500 gets glassy like obsidianBrazilian Agate 450 – 600 Hold for 1- 2 hoursRhode Island Jasper & Chalcedony 300 - 350 Most Flints & cherts 400 – 550Mook Jasper 425 – 550India Agate (Bloodstone) 450 – 500 More Transp. less heatMexican Agate 500Most Jaspers 350 – 500Red Jasper 450 – 500Picture Jasper 500 – 600Sunset Jasper (Richardsons Ranch) 400 – 500 Gets brittle over 500

Turns yellow at 400, orange at 425, dark red at 450 – 475 Petrified Wood 300 – 480Moss Agate 450 – 500 More transp. Less heatCoral 450 - 600

Things to Think AboutAsk 3 different people about Temperatures, ramp times, or hold timesYou will get 10 different answers. Nothing is ‘set in stone’ !

Reasons for Fracture or Pot-lidding during Heating

1. Dissimilarity of material within a piece of rock2. Not drying out the rock enough3. Ramping up temperature too fast4. Cooling too fast5. Too high a holding temperature6. Some stones will just crumble if too high a temp7. Air or liquid pockets in the rock will go BANG !8. Most of the temperatures and holding times are from Knapping sites. So for lapidary I would increase the holdingTimes to get more color depth.9. Longer holding time = deeper color

Do Not handle HOT ROCKSLet them cool or use tongs

What to ExpectMost flints and cherts will benefit from heating.Glossiness, transparency, and workability will improve.

Agate & Jasper benefits

1. Finished Cabs will be glossier. 2. Slabs will feel smoother and have a waxy feeling.3. Slabs will work into cabs in less than ½ the time4. Colors will change or intensify5. Color change and intensity can be different in

sequentially cut slabs.6. Color depth may vary depending on thickness,

temperature, and holding time.

What I have for Display

1. Rough or Slab Unheated2. Slab heated3. Unheated Cab4. Cab made AFTER Heating Slab5. Cab made Before Heating Slab

Some of the display pieces I did not have enough materialTo provide all 5 display pieces. However, there are someAdditional pieces that show the effects of heat treatment.

Note the color differences between the differentPieces of the same stoneAlso, while it is difficult to see here, on the flaked piecesYou will see a waxy/glossy surface to the flaked portionsSome stones may have a “healed” fracture, they may orMay not break during heat treatment

(Display Pieces on following Slides)

The following display items were glued on butcher paperSo that it was a ‘hands on’ experience for those attendingThe meeting presentation. I have included some extra notesThat were brought out verbally at the presentation.

I use an old roaster oven, purchased at Goodwill for $15.00And sand.

I started with a drying temp of 200 for about 4 hours, then rampUp to 475 at about 100 deg/per hour.

Hold time was about 6 hours then ramp down. As the sand holdsThe temperature up pretty well in my roaster, I usually just Turn it down to 250 then when it starts to kick in to heat up again, I turn it off.

Depending on how full it is, (3 Layers of sand and rock) I willJust turn it on to 500 deg. It will take about 2 days to reach 475. Then I just turn it off. (A newer unit may work better) And anotherDay or 2 to cool down.

Do not be afraid to experiment ! Above all else, HAVE FUN !!

Plume Carnelian

Unheated SlabBanded Carnelian

Unheated

Cabbed then Heated

Heated then Cabbed

Heated Slab

Un Heated Cab Un Heated Cab

Heated Slab

Heated then Cabbed

Cabbed then Heated – Fracture popped off during

cabbing

Banded Agate

Unheated SlabSunset Jasper /

Polka Dot Unheated

Cabbed then Heated

Heated then Cabbed

Heated Slab

Un Heated CabUn Heated Cab

Heated Slab

Heated then Cabbed/Flaked

Cabbed then Heated

Blue Brazil

Unheated SlabBrown Brazil

Unheated Slab

Cabbed then Heated

Heated then Cabbed

Heated Slab

Un Heated Cab Un Heated Cab

Heated Slab

Heated then Cabbed – Healed fracture, broke when cabbing

Cabbed then Heated – healed fracture did not

break

Montana ??

Unheated SlabRed Carnelian

Unheated

Cabbed then Heated

Heated then Cabbed

Heated Slab

Un Heated Cab Un Heated Cab

Heated Slab

Heated then Cabbed

Cabbed then Heated

Brazil - Fractured & Pot Lidding

Ramp up too fast, & cooled too fast

Brazil, heated too fast not long

enough

Brazil, Tumbled then Heat Treated

Notice the color depth on the flaked edge

Notice the lack of color depth on

ground and flakedareas