Play-Doh can be hardened by placing it on a non-stick pan or cookie sheet and baking it at 200 F for five minutes. When it is removed from the oven, poking it with a toothpick allows one to determine its hardness.
The best way to preserve a Play-Doh masterpiece is to photograph it. Play-Doh is designed to be used over and over, so when it hardens naturally, it cracks. Play-Doh started as a wallpaper compound used to remove soot deposits from walls. It was non-toxic and easier to mold than modeling clay. Play-Doh hit the market in 1956. More than 2 billion cans equal to 950 billion pounds have sold worldwide.