How to make a mold for casting handmade paper pulp. Make a model with oil base clay and cast mold using liquid latex and plaster.
Make your own unique low relief molds for casting paper pulp. You may want to choose a theme or series to create several molds. Some suggestions are flowers, masks, butterflies, birds, fish, landscapes and other decorative images.
You will need the following supplies:
A rigid surface or board for a work surface - foam core, thick cardboard or shower board work well
A shallow box the same size as the board or slightly larger
Oil base clay - Quantity depends on the size of your piece and you may want to get it at a sculpture supply store if you are making a large piece
Plaster - you can get this at your local home improvement store or craft store
Brush on liquid latex or rubber (optional) - usually found at sculpture supply stores
Various clay tools or household utensils for carving and shaping your model
Planning your project
Keep it sized within the borders of your board with several inches free of clay all around the perimeter of your project. You may want to sketch your idea first or you might want to plunge right in and work spontaneously with the clay. Brainstorming on paper is often a good first step to releasing your creativity. Reference books are always helpful for creative resource material.
Prepare your clay
Softening your oil base clay will make it easier to handle. Cut your clay into smaller chunks and put it on a tray. You can use a heat lamp over the tray to keep your clay soft. You can also soften your clay by putting it in a bowl and setting it in a pan of hot water. Simply handling oil base clay and kneading it will warm and soften it as well.
Sculpt Your Model
Begin by laying down a base of clay upon which you will continue to add detail to form your design. You will be alternatively adding and subtracting clay and cutting in designs with your tools and fingers as you proceed creatively to unfold your design. Avoid very deep designs with undercuts. You will not be able to remove your paper casting if your design has deep undercuts.
Prepare Your Box for Casting
The top edge of the box should be about 1 inch or more above the highest point of your clay model. Check all corners, folds and edges of your box to be sure there is no point where plaster can leak out. You may want to run a smooth bead of caulk or oil base clay on the inside corners and folds of the box. If using clay be sure to press it tight into the corners and folds to ensure a tight leak proof box. Place your board with your clay model into the box and tape it in around all the edges so no plaster will flow under the board. I use duct tape and find that it works well. Duct tape around the outside perimeter of your box to add strength to the sides to ensure that your box sides won’t buckle. It never hurts to take extra precautions.
Cast your Mold
If your design has a lot of fine detail you will want to use the two step process. If your design is moderately simple and smooth with larger smooth shapes you can eliminate the latex layer with satisfactory results.
Step 1 - Cover your clay model with a thin coat of mineral oil or mold release agent.
Step 2 - Paint liquid latex in a thin layer over the entire surface of your model working out onto the board. While the first coat is still tacky lay on a second coat and lay down a single layer of cheesecloth into the wet latex. While this layer is still tacky lay down a third layer of latex. If you see any areas that seem particularly thin lay on another coat or two of latex allowing each layer to become partially set but still tacky. Allow a full 24 to 48 hours for complete curing before proceeding to the plaster step.
Step 3 - Prepare enough plaster to fill your box. Follow the directions on the plaster bag and wear a dust mask. Add plaster to your bucket of water not the other way around. It is better to have too much plaster rather than too little.
Step 4 - Gently pour plaster to fill your box. Do not dump it in or slosh it in. The idea is to avoid causing air bubbles or disturbing your backing board or model. When the plaster has covered your model continue to fill at least 1inch beyond the highest point of your model. Tap and jiggle the box gently to release air bubbles.
Step 5 - Drying time varies with plaster from several hours to sometimes several days if you are doing a large mold. Be sure that your plaster mold is dry before removing your model. When dry, tear away the sides of your cardboard box and discard it. Turn over your mold and remove the clay model. Yes, you will likely destroy your original in the process. Clean out any remnants of clay and completely clean your mold. You are now ready to cast your handmade paper pulp. See this factoid Creating Handmade Paper Pulp In Your Kitchen