Page:Theophrastus - History of Stones - Hill (1774).djvu/233

 XCV. There is alo a kind of this made of Ochre, by burning, but it is not nearly o good as the others. The making this was an Invention of Cydias, who took the Hint of it, as is aid, from oberving, in a Houe which was on fire, that ome Ochre which was there, when half burnt, aumed a red Colour.

XCVI. The way of making the factitious is this: They put the Ochre into new earthen Veels, which they cover with Clay and et in Furnaces; and thee, as they grow hot, heat alo the Ochre, and the greater Degree of Fire they give, the deeper and more trongly purple the Matter becomes. The Origin of the native Kinds eems to tetify that this Method is not irrational, for all thee eem to have uffered Changes by the Action of Fire: