Kiln For Metal Clays

Precious Metal Clay or Art Clay can be fired in any furnace that will sustain the required temperature with reasonable stability. Almost any kiln with a pyrometer, like those used for burnout or enameling, will work. The kiln should be located away from combustible surfaces and plugged into a properly wired socket so that its cord cannot be snagged or tripped over. It's helpful to have work gloves, long-handled tongs and a heat-resistant surface like a brick in front of the kiln to set work on when it comes out of the kiln.

We sell a programmable kiln that maintains a selected temperature for a set length of time, then shuts off automatically. Though not essential for success with Precious Metal Clay or Art Clay, this unit is designed specifically for silver clay and makes the firing process as foolproof as the modeling.

Shrinkage

When Precious Metal Clay or Art Clay is fired, the water and binder vaporize and disappear completely. Because these together make up about 30% of the original Precious Metal Clay or Art Clay, the object after firing is reduced to about 70% of its original size. This offers exciting possibilities because the shrinkage is proportionate. All the images, textures and details you create in the clay original will be retained in the final version-0nly smaller! This is a little like using the reduction button on a photocopier and nearly as easy. PMC+ has a higher metal content. Fired PMC+ pieces are 88% of the original size.

As the following chart describes, shrinkage, density and hardness all increase with time and temperature. That is to say, if you "short fire" Precious Metal Clay or Art Clay you will make it weaker. The longer the firing process the denser the metal, achieving maximum at the durations shown below.

Firing at temperatures above these risks melting the material-it's real metal and will melt just like conventional metal when heated to its melting point. Pieces may be fired any time after they are made, though pieces with widely varying cross sections should be dried slowly to prevent cracking. Flat pieces are laid directly on a kiln shelf, fire brick or clean soldering pad and set directly into the kiln. Work can be very close together as long as the pieces don't touch each other. Contoured or hollow pieces require a little more care to ensure that they don't slump or collapse during the process. Support these forms on vermiculite, or alumina hydrate powder, available from us. It can be reused almost indefinitely so a couple of pounds should be enough for most studios.

Steps in Firing

Set the completed Precious Metal Clay or Art Clay object on a heatable tile, cradling it in a bed of alumina hydrate if the form is other than flat (middle drawing above).

Set the tile into the kiln on bits of brick that lift it off the floor, facilitating both heating and removal of the object.Program and start the kiln or, if firing manually, turn it to a high setting. Precious Metal Clay or Art Clay does not need to be vented, though when other materials are included (like cores), ventilation may be necessary.

If you have a manual machine: When the pyrometer indicates that the correct temperature has been reached, turn the dial back slightly to ensure that the temperature does not go higher. Check the clock and maintain this temperature for at least two hours. There is no disadvantage in heating the work longer. When many pieces or a sagger box is used, a longer time is recommended to ensure complete fusion. When the time has passed, turn off the kiln.