shrinkage is just a fact of life. The photos at left show two pendants that were made with FASTfire BRONZclay™ before firing and after firing. The shrinkage rate for this type of clay is roughly 10%-12%. The original formula of BRONZclay is about 25%. The rate varies with metal clays made of silver as well. So when forming a piece, the shrinkage rate has to be taken into account so it will fire to the desired size. I find bronze metal clay to be temperamental in this aspect as well as others. Because there are so many temperature variables inside a front loading kiln (i.e. cooler near the door, hotter at the back and sides), pieces can vary in the amount of shrinkage and sintering. Earrings can sometimes fire unevenly resulting in one earring being slightly larger or smaller than its mate – not good! The finished color can vary as well with shades of bronze ranging between golden, red, green, and grey all from the same kiln load! Sometimes this is desirable – often times it is not. Bronze metal clay is definitely the “new kid on the block” in terms of having all the “bugs” worked out. Bronze metal clay has only been around for several years so it doesn’t have a long track record. Hopefully, the formulas will improve over time offering more consistent results. Those of us working with bronze metal clay are charting new territories so to speak – finding out what works and what doesn’t. I love working with metal clay, especially silver metal clay which doesn’t present these problems for me and I will happily start using it again – if silver ever drops to a reasonable price again!
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