The fourth kind of earth that Theophrastus mentions is the kind that takes its name from Tymphaia, a district in northern Epirus; he seems uncertain whether to classify it as another kind of native earth or as gypsos. The same uncertainty can be seen in section 63, where he says that the people near Mt. Athos use the Tymphaic earth for clothes and call it gypsos. On the other hand, he states in section 64 that gypsos occurs in Tymphaia, so that he probably regarded Tymphaic earth as identical with gypsos. Therefore, it would seem that Tymphaic earth was either a natural kind of gypsos or a substance that closely resembled one of the minerals included under this term. It may have been an earthy gypsum or a white chalk.
62. gypsos. Although the English word gypsum is derived from the Greek word γύψος, which has often been translated in this way, the descriptions given by Theophrastus in the rest of the treatise show clearly that, in his day at least, the Greek word had a much broader significance. It is, however, certain from some of these descriptions that gypsum, natural hydrated calcium sulfate, was included under the name gypsos. On the other hand, it is equally certain that the Greek term was also applied to the artificial partly dehydrated calcium sulfate now known as plaster of Paris. Moreover, some of these descriptions show beyond doubt that gypsos must have included a very different substance, our present quicklime or calcium oxide. It apparently also included various preparations made from these different substances. The evidence for the use of the word is discussed in the notes on the remaining sections. Theophrastus not only fails to make distinctions between the different chemical substances included under the term gypsos, but he often confuses one with another.
62. Painters use only the Melian kind; they do not use the Samian, even though it is beautiful, because it is greasy, dense, and smooth.
Samian earth is not mentioned as a paint pigment by other ancient authors, and it is easy to understand why a material of this nature was not used. There are, however, many allusions in the
