Gesso is a powder made from calcium carbonate and glue. Applied to wood, it hardens to a brilliant white and can be used a primer or sculpting material. Gesso was traditionally used as a base for tempera and was a favorite of Renaissance panel painters. It can also be used on furniture and moldings, where it can be built up and carved. Gold leaf is normally applied to wood on top of a layer of gesso.
Things You'll Need
Plaster of Paris
Coloring agent (optional)
Mix together one part plaster of Paris and four parts water. Let the mixture sit until the plaster settles to the bottom. Pour off the water and remix. Repeat this process three times. The plaster reacts with the water. If the mixture gets warmer than when you started, repeat the process. If it appears to be the same temperature as when you started, then your plaster is slaked, which means it's ready for the next step.
Scoop out the plaster of Paris and let it dry completely. Break up any clumps that appear as they may contain areas of moisture. Use a common kitchen grater to grind it into a fine powder.
Mix three parts plaster of Paris to 1 part glue. Add several drops of honey to every tablespoon or so of this mixture. Mix thoroughly and pound out any lumps. Your mixture should have the consistency of pancake batter.
Store the gesso in an airtight container. Add a little water if it becomes too dry.
You can also make gesso with chalk instead of plaster of Paris. Just make sure the chalk is real chalk and not a synthetic substitute.
To color gesso, simply mix in a coloring agent. You can use watercolors or gouache.
Do not dry slaked plaster of Paris in an oven. Too rapid drying can cause it to turn back into regular plaster of Paris.