Anyone who's ever played with the stuff knows that it's not just for modeling. Sure, you can shape it into a dog, a flower, a fish or a tree, and if you leave it to dry, your creation will harden into a sturdy, solid piece. But you can also mash it, squash it, pull it, roll it and cut it just for fun.
The most popular use for the dough, besides eating, is extruding. Many Play-Doh toys let you press the dough through a mold to create long ropes and other shapes. The first of these toys -- the Fun Factory -- hit the market in 1960, and versions of it are still available today. In other Play-Doh toys, extruded dough turns into a range of long, noodly objects, like a dog's tongue, soft-serve ice cream and hair that can be cut and styled.
Play-Doh compound can do all of this because of the interactions between its ingredients. The exact ingredients are a closely guarded secret, but Hasbro, the company that makes and distributes the compound, does reveal a few facts about its basic composition. The dough contains water, salt and flour. It doesn't contain peanuts, peanut oil or milk, but does contain wheat.
According to the current Play-Doh patent (U.S. Patent 6,713,624), the compound is essentially a starch-based binder mixed with water, salt, lubricant and preservative. To be more specific, it contains:
Each of these ingredients has an effect on the compound's texture, fragrance and appearance. One of the major contributors to the softness and texture of Play-Doh compound is the interaction between its two primary ingredients - starch-based binder and water. To understand how the dough works, you have to know a little about starch and what happens when it comes into contact with water.
We'll look at the chemistry behind starch in the next section.