PLEASE NOTE: When I did this project 10+ years ago with my students, I didn't know that some vermiculite is contaminated with asbestos--certainly not something to which students (or teachers) should be exposed!
I don't know if it would be possible to mix the plaster with fine-textured sawdust instead of vermiculite in order to get a similar carving medium, but please be aware that vermiculite may not be safe to use.
If you come up with a good alternative material, please let me know!
Plaster of Paris
Fine-textured vermiculite (SEE CAUTION ABOVE)
Water, bowl, measuring container
32 oz. Styrofoam cups (to be used as molds)
Gallon size plastic bags
Clear acrylic sealer
Show examples of abstracted/non-objective art and have students notice the emphasis on shape and form. (Optionally, show examples of primitive sculptures.) Explain that students will be carving into a soft, crumbly material that is not especially suited to highly detailed work, and they must, therefore, plan simple designs.
1. Mix plaster, vermiculite and water according to these ratios: 3 parts vermiculite, 2 parts Plaster of Paris, 2+ parts water. Mix together dry ingredients in a large bowl or bucket. Add water, and let sit until it stops bubbling (a minute or two). Mix well with hands, squeezing out all the lumps. (If a quart measuring container is used, the ratio will be 3 qts. vermiculite, 2 qts. Plaster of Paris, 2 qts. + about 1/2 cup of water. This will yield four 32 oz. cup molds.)
2. After mixing, immediately pour into 32 oz. Styrofoam cups and tap sides of the mold to bring air bubbles to top.
3. Allow to harden (at least over night) and cover molds with plastic bags to keep fresh until ready for use. (If sealed in a gallon ziplock bag, this mixture will remain soft enough to carve for at least four weeks!)
4. When the mixture has hardened, carefully remove mold.
5. As the material is very soft and will still be very damp, a plastic knife is a good carving tool. When the work is finished for the day, return it to the plastic bag to keep it moist until the next class period.
6. Students may carve by setting the block inside of a shallow box (a copier paper box lid is ideal) as this will contain the mess. The carved material may then be dumped out in a trashcan OR it can actually be modeled with the hands to create another sculptural form.
7. Once the desired shape is achieved and the stray crumbs have been carefully brushed away, allow to dry. This may take several days, depending on the heat and humidity. As the work dries, it will become lighter in color, lighter in weight, and will no longer feel cold or damp to the touch.
8. Seal with one or two coats of acrylic sealer, and mount, if desired, on a wooden base.