For each head, roll clay into an egglike shape about 1 inch high and 1-1/4 inch across. Holding one head horizontally and referring to the photo, use a palette knife or toothpick to press a triangular shape (for a nose) into the center of the head. Repeat with the other head, holding it vertically.
Cut a 6-inch length of wire. For crafting ease, push one end of the wire into the center back of one head and push the opposite end into the plastic-foam sheet. Repeat with a second piece of 6-inch wire on the other head. Allow the heads to dry. Note: During the drying process, fill any cracks that appear with additional clay.
To make each hat, use clay to create a column about 1/4 inch tall and 1/4 inch across; use clay to create a thin flat circle about 1/2 inch in diameter for each brim. Shape the column into a cone for a witch hat. Slightly narrow one end of the other column for a top hat. Press each shape into a brim. Turn up the brim as desired. Cut two 6-inch lengths of wire. Push one end of each wire into the bottom of each hat and push the opposite end into the plastic-foam sheet to dry. Allow the hats to dry.
Paint the heads antique white. When the white paint is dry, paint the noses red. Referring to the photo, paint toothy grins and dot-and-circle eyes with black. Let the paint dry. Paint the hats black. Allow the paint to dry. Remove the hats from the wires and glue to the heads using 5-minute epoxy.
Following the manufacturer's directions, cover the heads and hats with step 1 of the crackle finish. Let dry (about 15-20 minutes), then cover the heads and hats with step 2 of the finish. Let dry overnight. Mix a small amount of black paint with antique white to create the desired shade for the cracks. Following the manufacturer's directions, add acrylic flow release and water until the paint is runny. Apply the mixture with a paintbrush to a small area, then rub it into the cracks with your finger. Wipe away the excess with a dry cotton rag, then wipe the surface with a damp rag so the color ends up only in the cracks. Repeat to cover the entire head. Finish the heads with two thin coats of polyurethane varnish; let dry between coats.
To frame the heads, clip the black head wires so they extend about 1 inch from each head. Decide where to position the heads in the shadow box and mark each position with a dot. Using an awl, poke a hole (the diameter of the wire) at each dot. Glue the wires into place. Close the lid.