Plaster of Paris is a white powder that, when mixed with water, forms a smooth paste that hardens quickly into a solid.

You've probably seen plaster of Paris in action: doctors use it to make casts for broken bones, artists use it to create sculptures, and builders use it to repair walls or create decorative moldings. When you mix the powder with water, you have about 10 to 20 minutes before it begins to set, which means it starts getting warm and hard. Once hardened, it becomes strong enough to hold a broken arm in place while the bone heals, yet light enough to wear comfortably.

The material has been used for thousands of years. Ancient Egyptians used it to coat the inside of pyramids, and Renaissance artists used it to prepare surfaces for their paintings. Today, it's still popular for school art projects because it's inexpensive and captures fine details beautifully. If you've ever made a handprint craft or built a model volcano, you might have used plaster of Paris. The key is working quickly once you add water, because unlike clay, which stays workable, plaster waits for no one.