Let them eat... play-dough?
My children eat play-dough. Shamelessly, persistently and with gusto. So I decided early on that instead of denying them the pleasure of squeezing, burying, cutting, stamping and rolling play-dough, I would give my two boys (ages 2 and 4) homemade dough instead of the kind that comes in canisters.
(Commercial play dough is technically not toxic, but it is not intended to be eaten, and contains lubricants which are probably petroleum based, as well as preservatives. Here's a good article about the science behind it.)
We make play-dough on a weekly basis, often from the same recipe, but sometimes from recipes online. The quality and texture of these online recipes vary widely. One week our play dough might be perfect, another too crumbly and dry, and sticky and gooey the next. The nerd in me wondered what made them turn out so differently, and the mom in me was sick of vacuuming crumbled play dough and scraping gluey formulations from my chairs.
So, inspired by "Cook’s Illustrated", I decided to try dozens of play-dough recipes, using friends as testers, to isolate the best recipes.
Here comes the science bit
Play-dough contains five basic ingredients: flour, water, salt, cream of tartar (or other acid) and oil. The variables that most affect texture are the cream of tartar, salt and the type of flour used. The flour and water compose the bulk of the dough, and most recipes I found contained equal amounts of flour and water. The proteins in the flour (gluten for wheat flour) interact with the water and heat to become a stretchy, elastic mass. Salt acts as a preservative, and also adds texture and body to the dough. The oil acts as a lubricant and helps to keep the dough moist and not sticky.