Homemade plaster can be created by mixing 2 cups of salt with 2 ? cups of hot water, then adding it to 4 cups of flour. The mixture is hot after it is mixed, so be sure to let it cool before attempting to imprint anything that would melt or be damaged by heat.
In a pot, bring 2 ? cups of water to a boil. Add 2 cups of salt, and let the salt dissolve in the hot water.
In a separate bowl, measure 4 cups of flour. Pour the hot salt and water mixture into the flour, and stir it with a spoon designed to handle high heat.
When dough is cool enough to touch, remove it from the bowl and place it on a surface to knead. It may be helpful to place the dough on the cookie sheet you plan to bake the plaster on so there is less chance of it breaking or stretching out of shape when transferring it.
You can then form shapes with the dough that you later imprint. This can be done by using cookie cutters or other kitchenware that allows you to carve and create distinct pieces. Place what you want to imprint in the plaster.
Bake the plaster with the imprint at 225 degrees Fahrenheit for roughly three hours. Once the imprinted shape in the plaster is completely baked and cooled, you can decorate the image by painting the imprint or the area around it.