Post #377230 by Babalu on Wed, Apr 30, 2008 11:02 AM

Grog is sooo right! This should have been discussed in the beginning. As you are sculpting your master you will need to take into account that clay shrinks as it dries...it also shrinks during the firing process. A typical shrinkage rate (depending on your clay body) is between 4% and 10% as the green ware (unfired clay) dries. Clay can also shrink as much as 8% in the firing of the clay. Some clays have more "grog" (no pun) added to them which will reduce the shrinkage rate during firing. Grog is is finely ground bisqued clay that has been added to the clay. This added grog not only reduces shrinkage, it also makes for a more sculptural clay, and helps with the thermal shock of the firing.

Most of the mugs that you guys like are made with low fire (cone 04) slip. This type clay shrinks a bit, but one can also get some really nice store brought colors with the low fired glazes (cone 06) that are available for this type of cone 04 clay.

I would venture to say that this mug of mine shrinks a total of approximately 12-14% during the drying and firing.

I know Bowana still has some "how to" mold making photos to post yet. After he has done that I will dive a little into glazing and firing for you.

Thanks Grog for catching the shrinkage thing...