What Clay Should I Use?

A mid range stoneware with a little grog in it. Grog forgives uneven walls, holds a shape while you decide what you meant, and cracks far less while it dries. Smooth porcelain does the opposite of all three. Nearly every body on the chart marked grogged and mid range is a reasonable first bag.

Porcelain is a kaolin body: whiter, tighter, often translucent where it thins out, and with a shorter distance between standing up and sitting down on the wheel. Stoneware carries more plastic clays and usually some iron, so it is warmer in color, stiffer under your hands and much more forgiving. Both vitrify. The chart shows porcelain absorption clustering under 1 percent and stoneware spread across 0 to 3.

Multiply. A 12 percent body means a 10 inch wet bowl comes out of the glaze firing at about 8.8 inches, and a 12 inch platter loses nearly an inch and a half. It also means anything that cannot move as it shrinks will crack: a handle joined too dry, a slab held flat on a board, a foot ring stuck to the shelf by a glaze run.

Under 1 percent is fully vitrified and the safest place to be. Between 1 and 3 percent is where most functional stoneware lives and is generally fine under a fitted glaze. Over 3 percent, the body itself is holding water, and an unglazed foot ring can weep onto a table days later. That is a clay decision, not a glaze decision.

Both, depending on what you are making. It cuts shrinkage, resists thermal shock, holds a tall wall up and lets a thick sculpture dry without splitting. It also scours your fingertips on the wheel and leaves a surface that will never be glassy smooth. There is no better body, only a body suited to the job.

You can, and it will come out underfired. The body will not vitrify, so it stays porous and weak, and the glaze fit is a separate gamble on top of that. It is a fine way to make something decorative and a poor way to make a mug. Firing the other direction, a cone 6 body taken to cone 10, is worse, because that ends with clay on the kiln shelf.

Usually because one of them is quoting an older formulation, or tested at a different cone, or reprinted a figure with a digit moved. It is common enough that we stopped picking a winner. Rows on the chart marked with two figures are the ones where the published record disagrees with itself.

No. Everything fired here has to be clay bought here, because a body meant for another temperature can bloat, slump or run in a kiln set for ours, and what it damages is shared. Clay you bought here, took home and brought back is fine.