Take one part plaster of Paris to three parts water. Sprinkle plaster into the water in a container with a lid and rock it on your knee for 8-10 hours continuously. Set this aside and let plaster sink to bottom. Shake it for a couple of minutes. Shake like this three times a day. Do this for the next month.

• What to do with your slacke plaster: Pour off water and take the wet plaster and make it into cakes to dry in the sun. Mix rabbit skin glue with the plaster to make gesso.