Testing new clay body

The initial testing has begun. I started by looking at the shrinkage of the clay body. Different clays shrink more than others at different temperatures. Clays which have very fine particle sizes will shrink more than clays with larger particle sizes. Porcelain has very fine particle sizes which makes it very plastic and also shrinks the most, some as much as 15%. Whereas, groggy clays shrink less because they have a lower water content to start with.

I wanted a clay body with the lowest shrinkage percentage when fired and therefore have been adding different percentages of molochite (grog - clay which has already been fired and then ground to various particle sizes) to my clay body.

For this, I made some plaster boards. I began by simply making some acrylic moulds to pour liquid plaster into, leaving it to set. When dry, the plaster boards absorb the water from the different clay slips, making the clay bodies workable by hand.

I added different amounts of molochite at 5%, 10% 15% and 20% to the dried out clay. I mixed them with water then poured onto the dried plaster board.

Two different percentages of molochite added to two clay drying on a plaster board

By making some tiles with 10cm lines marked on each of them, post firing it will tell me how much each line has shrunk letting me know how much molochite is needed to have the desired shrinkage.

Tiles with 10 cm line before firing

Keep an eye for fired updates.