Plaster of Paris, also known as gesso, is a mixture of gypsum that, when mixed with water, forms a mouldable clay that dries and hardens without the need for a kiln or oven. It has been a staple of elementary school science projects for years because the characteristics of plaster of Paris make it so easy to work with.
Although the use of plaster of Paris in elementary school art sculptures and science experiments remains common, there are dangers you should be aware of. According to a Material Safety Data Sheet from a manufacturer of plaster of Paris, the material releases heat as it hardens and can cause severe burns, resulting in irreparable damage to body parts encased in moulds made using plaster of Paris. Breathing dust from plaster of Paris irritates lungs and nasal passages and when ingested or inhaled, the dust absorbs moisture and begins to harden in the body. The International Agency for Research on Cancer sites this type of material as being carcinogenic to humans. The use of gloves, safety glasses and proper ventilation is recommended when using plaster of Paris.
Use plaster of Paris to demonstrate how fossils are made. Mix plaster of Paris and pour it into a pan. Use petroleum jelly to coat objects like sea shells or plastic fish and press them into the pan. Remove them to leave an impression in the plaster of Paris and let the new fossils dry. Small plastic dinosaurs may also be used to make fossilised foot prints.
In chemistry, an exothermic reaction is a reaction that releases heat when materials are combined. A mixture of plaster of Paris and water releases heat making it a simple science experiment to demonstrate an exothermic reaction. This same mixture demonstrates a chemical reaction between plaster of Paris and water and the way a chemical reaction can be used to produce heat.
An elementary science project in forensic science uses plaster of Paris to demonstrate how moulds are made of footprints and tire tracks. A method of making the moulds is demonstrated as well as how the moulds can be used to help solve a crime.
Excellent science fair projects demonstrate, and make it easier to understand, how a scientific process works. An experiment in geology demonstrates how freezing water makes cracks in rock. Mix plaster of Paris and pour it into two milk carton halves. Fill a balloon with water to the size of a golf ball, tie a knot in the end, insert it into one of the cartons and let it cure for an hour. Put both cartons in the freezer over night. The plaster with the balloon should crack as the water freezes.