was never present there, since a fairly large local deposit could have been completely worked out by ancient operations.
42. When it is heated in the fire and dipped in oil, it becomes very blac\ and hard; and dishes for the table are made out of it.
The blackening of die stone when it is fired and dipped in oil is a phenomenon that is readily understood. If the stone dishes were heated to the proper temperature and then dipped in a vegetable oil, which probably was the kind employed, black carbonaceous matter caused by the pyrolysis of the oil would be deposited on the surface of the stone and to some extent in the pores below the surface. A simple experiment was performed which showed how readily this takes place. One end of a green soapstone block ten centimeters long, three centimeters wide, and one centimeter thick was heated in a gas flame until it was red-hot, and then the entire block was plunged into olive oil. No change of color was observed during die heating, but when the block was plunged into the oil die heated part became black rapidly, while the relatively cool end of the block simply darkened slightly from absorption of oil by the stone. The blackening was more intense and occurred more rapidly in the place where the stone had reached the highest temperature. When the process had been repeated twice, the color of the part that had been treated became a deep black. Possibly this method of successive treatments was the one actually employed in ancient times, tiiough Theophrastus does not say this. It was also noticed that the blackened stone had a somewhat greater surface hardness than either the untreated stone or the stone treated with oil at room temperature. The results of the experiment show that the statements of Theophrastus are quite accurate in this passage, as they are in other parts of the treatise whenever he seems to speak from his own knowledge. Probably die main purpose of treating the stone with oil was to harden it and make it less porous, though the process may also have improved its appearance. Dishes and other objects made of various kinds of steatite were widely used in ancient times, as is shown by the large numbers that have been found. Black examples are not uncommon, but apparently it is not certain whether their color
