Segment 1 heats the wax to 300°F/148°C and holds it for one hour, allowing it to drip from the mold.
Segment 2 hardens the mold.
Segment 3 lowers temperature to 800°F/426°C, the typi- cal casting temperature for silver. (Most types of gold cast at 900°F/482°C.)
Note: Casting temperature depends on the size of the mold. The temperatures above are only a guide. See your jewelry supply dealer for temperature recommendations.
Burnout Instructions
1Place a metal tray inside the kiln on three ½” posts. Place the mold on a wire mesh screen on top of the tray. The mold’s sprue hole should be down. The tray will catch melting wax as it drips from the sprue hole.
2Keep the kiln’s vent hole(s), if any, open during wax elimination. If the kiln has no vent hole, leave the door open ½”. This allows fumes to escape from the kiln. Heat the kiln to 300°F/148°C and hold it at that temperature for at least one hour.
Note: Do NOT heat the wax above 300°F/148°C. Hold at 300°F/148°C for at least one hour. During this hour, the wax will melt from the mold and drip into the tray. If the kiln gets hotter than 300°F/148°C, the wax may smoke and deposit car- bon inside your kiln, causing expensive damage.
3 After one hour at 300°F/148°C, open the kiln. Remove |
the mold and wax tray. Pour the wax from the tray and |
leave the tray out of the kiln until your next wax elimi- |
nation. (Do not leave the tray in the kiln!) |
4 Heat the mold to the temperature recommended by |
your jewelers’ supply house where you purchased the |
mold material. This is usually around 1350°F/732°C. |
5 Lower the temperature to the casting temperature of |
the metal. Hold at that temperature until you are |
ready to begin casting. Remove the mold with tongs. |
Firing Mistakes
Silver Clay
Cracks
Cracks that appear in fired silver clay may be due to too much water in the silver clay before it was fired. Another cause is careless handling of a dried, unfired piece. To re- pair, fill the crack with silver clay and fire again.
Brittle
Silver clay will not reach full strength if underfired. You may be able to save the piece by firing again to the correct temperature and hold.
Too Much Shrinkage
When silver clay is overfired, it shrinks too much and loses detail. If the kiln is firing hotter than the temperature programmed, check the position of the thermocouple (see page 17, bottom left column). Replace the thermocouple if it is old.
Glass
Glass Cracking
Probable Causes:
■Heating the Kiln Too Fast
■Cooling the Kiln Too Fast
■Fusing Incompatible Glass
■Not Enough Glass Separator on Shelf
Most problems in fusing are caused by rushing the firing. The glass must change temperature slowly during the criti- cal temperature range of 100° - 500° F / 37° - 260°C. This critical range applies to both heating and cooling.
The second critical temperature range is annealing, which is the cooling range of 950° - 700° F / 510° - 371°C aver- age. Cool the glass slowly during this range so the stress in the glass will have time to dissipate.
Wear protective gloves and safety glasses. |
Saving a Carbon-Damaged Kiln
If you follow the above directions, your kiln should be safe from wax damage. In some cases, a small amount of carbon may form on the walls over a period of time. This is due to the burning of wax residue that was left in the mold. For this rea- son we recommend that you periodically fire the kiln to 1500°F/815°C as follows:
1Open the vent cover(s) or leave the door ajar ½”.
2Fire the kiln empty to 1500°F/815°C at a rate of 300°F/166°C with a one hour hold (01.00).
If you become im- patient after the glass has fused and you crack open the door of the kiln for a few sec- onds to peek inside, you may hear a “ping,” which is the sound of glass cracking. Avoid the temptation to open the door. Wait until the kiln has cooled to room temperature. Some artists schedule their fusing so that it is com- pleted before they go to bed. That way they will
Flaking glass separator can cause the glass to crack. This is because the glass sticks to the shelf.
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