Of course, the clay can be bought in the store. What of it? The radio also you can buy, but how many people pore over radiochemie!
For homemade clay only scarce raw materials will be, apparently, oleic acid,17H33COOH. However, it is probably in the school laboratory (and in General this is a very common acid, which is a part of almost all fat). From it we get the zinc salt is a zinc oleate. To 35 parts (by weight) is heated oleic acid add small portions of 5 parts of dry zinc oxide (you can take a self-made pigment). Each new batch of white make only after will disappear foam from adding the previous one. If zinc white you don't have it, you can replace them with regular chalk - then you get the calcium oleate. However, the quality of the clay is somewhat worse.
To the resulting syrupy the oleate add with constant stirring 18 parts of a mixture of equal amounts of oil and wax. To prepare it, melt the wax and add to it, vigorously stirring, a liquid oil such as vaseline. Once again would like to emphasize that all components should be thoroughly mixed, depends largely on the quality of the finished clay. As for the wax, then it would be better to take natural bee, but in extreme cases it can be replaced by stearin (not paraffin). Stearin can easily be prepared from soap, as described earlier.
When a mixture of oleate, oil and wax or stearin) is ready, add 23 parts of sulphur, crushed into a fine powder (you can take a pharmaceutical drug), 15 parts of dry fine clay, sifted through a sieve, and 4 parts of any mineral paint. You can, for example, take the mummy (iron oxide Fe2O3) - you already know how to cook this stuff (don't forget about the intense and constant stirring). Again stir the mixture and roll out with a rolling pin on a sheet of plywood or sheet metal. The clay is ready.
That's just what a nuisance: the oleate of zinc smell is not of the best. But it can drown odorant. Mixing original products, add a little (a few drops) pleasant smelling substances, such as pink or lavender oil or even Cologne.