A common casting medium, plaster is also a popular pick for making molds. Using this substance, which is manufactured in powder form, is ideal when you want a rigid structure to make casts as an alternative to using silicone or polyurethane molds. Many mixtures are called plaster of Paris—so named for the abundant deposits of pure gypsum near the eponymous city, originally used to make plaster—and are typically easy to prepare and easily workable. Other plasters as well as the plaster compound gypsum might be used for more specific or more demanding molding processes. No matter your pick, it’s important to exercise safety when handling plaster, which can be dangerous if inhaled.
1. Dap Plaster of Paris
Add cold water to this plaster of Paris powder to yield a slick plaster that stays workable for about 20 minutes. The fine particles mix smoothly into a consistent formula that dries to a durable shell with negligible shrinkage. Use it to pour a one-piece press mold or a two-piece mold that can be used and reused to cast a range of materials, from aluminum to wax. Sold in a convenient, eight-pound bucket, this is an especially smart option for those who need to make a large number of molds.
2. Amaco Pottery Plaster
This is the best choice for artists who work mostly with clay and need plaster for slip casting. The fine powder forms a super smooth plaster that dries to a rigid mold with high absorbency, which helps to pull water from the slip while preventing cracks. Stronger than plaster of Paris, the results can be used over and over again while achieving uniform ceramic pieces. In addition to slip casting, this plaster is well suited for making detailed sprig molds.
3. Falling in Art Plaster of Paris
If you’re new to mold making, start with this plaster of Paris, which is easy to work with in small quantities. It begins to solidify in about three or four minutes, yielding good-quality molds that can capture decent definition in less time than the competition. Because of this fast working time, however, you also have to stir it quickly. The resulting molds feel more brittle than those made of higher-end plaster and are unlikely to have similar longevity, but this plaster gives you a good feel of the process without breaking the bank.
4. Ultracal 30 Gypsum Cement
Formulated with 90 percent plaster of Paris and 10 percent cement, this gypsum boasts impressive castability and strength when dry. It also sets relatively slowly, providing a low and controlled expansion that makes it ideal for creating molds that demand utmost precision, durability, and longevity.
5. Docrafts Plaster of Paris
Designed for DIY projects, choose this kit plaster of Paris if you want to make cheap and easy molds. You get five pouches of powder—just over a pound each—to use or store as you wish. Simply add water and pour it over an enclosed clay form to create a basic mold. It is fast-setting, easy to demold, and results in molds that you can use several times over.