Calculator
Clay shrinkage and firing cost, make it bigger, pay by the inch.
The size to make a piece so it fires to the size you want, and what a studio will charge to bisque and glaze-fire it by the cubic inch.
Shrinkage
in
%
Firing fee
in
in
in
$
$
$
Make it this size, wet
-
A wet piece of the same size fires to-
Volume per piece-
Bisque, per piece-
Glaze, per piece-
All pieces, both firings-
Studios measure a piece as the box it fits in: length × width × height, times the rate, with a minimum charge per piece. The example rates are one studio's published list (Liberty Arts, North Carolina); others charge from about one cent per cubic inch. Use your own studio's numbers.
Shrinkage
Clay shrinks as it dries and again in the kiln. A clay's data sheet gives the total, wet to fired: Laguna lists 12% for its B-Mix cone 5. To end up with a finished size, make the piece larger: wet size = finished size ÷ (1 − shrinkage). A mug meant to be 4 inches tall is made about 4.55 inches tall in a 12% clay. The figure is an average with a tolerance, so fire a test bar of your own clay if the size really matters - a lid, a fitted part.
Firing fees
- Most community studios charge by volume: Davis Arts Center lists one cent per cubic inch with a $2 minimum for the first piece; Liberty Arts lists two cents for bisque and three for glaze with a $2 minimum.
- Some studios measure pieces at the greenware stage, before they shrink; ask which size they use.
- Small pieces often cost the minimum, so several small pieces can cost more than one bigger one of the same total volume.
- Full-kiln and per-shelf rentals are cheaper per piece once you make a lot; they are usually priced separately.
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