I notice that after firing my Art Clay with a torch, it no longer lies flat (when it was flat before firing). Am I firing too long, or not long enough?
Warping or distortion often happens if the flame of a torch is concentrated for too long in one part of the piece or when a piece is too large to be fired with a torch. A piece that is heavier than 25 grams or is larger than a half-dollar, in thickness and diameter, should be fired in a kiln.
If your piece is smaller than a silver dollar and less than 25 grams, go through this check list before firing your next piece:
The object being fired must be completely dry
If you are unsure if the piece is dry, place it onto a mirrored surface; let it stand for a moment then remove. If there is a haze at all on the mirror, the piece is not dry. Wait overnight before proceeding.
Place the dried piece onto a fire block
Do not use ceramic since it can crack or splinter when used for heating metal clay due to the concentrated heat in one area
Trace an outline of the piece onto the fire block
The outline will help you gauge how much the piece shrinks when fired. If the finished size is not 8% (or more) smaller than the original size, it was not properly sintered (fired). Start over.
Dim the lights in the room, if possible
The dim environment will enable you to assess the color of the glow as the piece is heated
Set a timer for the appropriate amount of time:
6g - 15g
16g - 25g
1 - 1.5 min
1.5 - 2 min
2 - 2.5 min
Put on your safety glasses
Start heating the piece with the torch. Be sure to keep the torch moving in a circular motion so as not to heat one part of the piece longer than the rest. Once it reaches a peachy salmon color, start the timer. Heat until the time is up.