Purchase molds, clear polyester casting resin, plastic or rubber gloves, and polyester catalyst ahead of class. Create a workspace where individual students or groups of students can create their paperweights. Cover the desk or table with newspaper or paper towels. Pass out gloves to all students to protect their hands.
Make sure the mold is clean and dry. Coat it with a thin coat of petroleum jelly or cooking oil and gently remove any excess. Mix about 6 to 8 ounces of resin -- or amount specified on resin container -- with the catalyst agent for about two minutes. Add glitter, if desired. Pour the resin immediately into the mold. Fill only halfway if you are adding an object inside the paperweight. Allow the resin to cure slightly; turn to a smooth, glossy, and transparent jelly substance, at room temperature.
Place an object such as a flower or bead into the center of the mold. Press the object down. Continue filling the mold with resin. Allow the resin to harden. Fill in any divots that develop while it dries. Continue to let the resin dry based on the directions for the specific resin you purchased.