There are many brands of plaster. I got a big bucket at Michael's. Check the ratio. Mine was about 2 cups plaster to one cup water. Mix, mix, mix! I poured the plaster into these red plastic solo plates that I found at walmart. They were pretty deep and in a nice shape. Give them a few taps to remove air bubbles.
You can see this painted fresco in the plate here.
This plate also made it easy for the fresco to pop out of when completely dry. It begins to harden right away setting up pretty good in 15 minutes and hard in 30 minutes depending on several factors. I would say leave them in molds for at least 4 hours to be completely hard.
We were trying to focus on Venice using the new exhibition as inspiration, but sometimes we just want to paint what we want! :) Here are some of our wonderful creations made at Drop in Art by children of all ages.
You will need:
-plaster of paris, water, measuring cup, disposable mixing bowls and disposable mixing utensils.
-solo plates
-paintbrushes
-tempera paints
This one is popped out of mold:


