Here is a fun way to try out painting on fresh plaster. All you need is some plaster of Paris, water, some plastic plates, and some paints.
Tempera paints can be used, but be sure to use a fairly undiluted paint-- because the plaster will absorb some of the paint, the design will tend to fade; you may want to put on a second coat of paint.
Using acrylic paint will result in brighter colors (less fading).
Here are some designs I made, using tempera paint:
I experimented with making some indentations in the plaster, also-- the design on the right has markings made with the end of a spool pressed onto the plaster, and the other two pictures had some lines made by "drawing" with a plastic straw (using something heavier, like a popsicle stick, didn't work well-- it went right through the plaster, tearing it).
Here are some plaster pictures by students in the 4th grade glass I was doing this project with:
Once the plaster is dry, it's easy to take it out of the plastic plate. (Please note: don't try to do this project using paper plates; paper tends to bond with the plaster instead of resisting it.)
It takes several days for the plaster to completely dry; in the meantime it is especially fragile-- so the pictures need to be set somewhere that they will not be disturbed.
This was a fun project; next time, I'd like to experiment with making different picture shapes-- maybe rectangular or square, depending on what kinds of plastic plates or containers I can find, to pour into.