Select the liquid rubber product size you need. The size you need will depend on the way you use the liquid rubber and the type of project you have. Liquid rubber can be found at your local art supply or craft store.
Place the object you want to make a mold of on a scrap piece of plywood or heavy-duty cardboard. Spray a mold release agent over the object so it will release easily from the mold.
Brush the liquid rubber directly onto the object that you want to make a mold of. It is important that you evenly coat all surfaces of the object with the liquid rubber in order to make a durable mold. Be sure to brush the rubber down onto the wood or cardboard work surface making an approximate 1/4-inch flange all around the mold. This will allow you to manipulate the mold when you fill it with the mold-making material (plaster, ceramic or resin). Wait for each liquid rubber coat to dry before adding another. You need at least 6 to 10 coats to make a durable mold.
Apply a layer of cheese cloth, or gauze tape, after brushing on each liquid rubber layer, if you want the mold to be long lasting.
Allow the liquid layers to dry thoroughly overnight. Remove the rubber flange from the plywood or cardboard base by gently inserting the box cutter blade under the 1/4-inch flange and gently loosen it from the base until the object and mold come off the base. Peel the rubber mold from the object. The hole left in the mold where it was attached to the base will be the area you pour your mold mixture into.
Fill a plastic container box with sand or soft dirt. Dig a hole, the size of the newly made rubber mold. Set the mold upside down in the sand so that it is held in place. The purpose of the sand or dirt is to hold the mold's shape so the mold should fit firmly in the sand without being misshapen.
Spray mold releasing agent inside the rubber mold so the molded item can be extracted easily.
Pour the molding medium (liquid plaster, ceramic or resin) into the mold. Wait for the molding agent to dry overnight or as long as needed. See your molding agent packaging instructions for drying time.
Remove the mold from the sand and gently peel it from your finished art piece.