Plaster Bat: a Round Slab Poured in a Frying Pan (Binns, 1910)

Put a quart of water in a kettle with a piece of soft soap the size of an egg. Simmer about an hour, until the soap has dissolved, and let it cool. Cold, it should be like maple syrup. The size keeps plaster from sticking to a surface.

Brush size onto the inside of the pan, wipe it off with a sponge, then wash with a second sponge and clean water. On metal one coat often does; repeat until the surface rejects water like grease. On the last coat don't wash: polish with the size sponge. Set the pan on a level table.

Take as much water as fills the pan about 1 in deep; Binns supposes a quart. Weigh 2 3/4 lb of dry potters' plaster for each quart and let it trickle through your fingers into the water in a jug. After about two minutes, when it has soaked up all the water it will take, stir with your hand to a smooth cream, breaking all lumps and removing air bubbles.

Keep stirring gently until the mix thickens and leaves a white coating on your hand that won't shake off. Then pour it into the pan and shake gently to level it. Poured right, it sets smooth and mat, like sugar icing. Poured too late, it is stiff and hard to level; too soon, it curdles with water on top. Wash the jug at once in a tub, never down a sink: plaster chokes the drain.

After about ten minutes the bat grows warm: setting is complete. Hold the pan upside down by the handle and rap its edge smartly on a brick or stone. The disc falls out. Scrape its edge and set it aside. Binns suggests making half a dozen for practice.