Flintknappers find that heat treating some kinds of stone improves the “knappability” and makes it easier to work. Heating some types of stone to certain temperatures for certain lengths of time actually changes the internal structure and the way it flakes. Typically, the stone gets a glossier or waxy look and might change color. In western Wisconsin, Prairie du Chien chert was often used for making stone tools in precontact times, but much of it is poor quality. We often find tools and waste flakes of heat-treated PDC. Often they are a pink or rosy color. The photo shows untreated chert on the left, and heat-treated chert on the right.