This use of gypsum to take impressions from flat moulds is suggested by Theophrastus, it would seem, in his treatise on mineralogy,[18] in which he says that plaster “seems better than other materials to receive impressions.” The term ἀπόμαγμα means nothing more than an impression, such as one makes in wax from a seal ring, and such as is common still in plaster; it is to this use that he seems to refer. He does not say, however, that gypsum was really put to this use; and if it were, it would advance us little in our inquiry, since any material which is soft will receive an impression, whether it be bread, pitch, clay, wax, or any similar substance. But the step from this simple process of stamping in a shallow mould to casting from life or from the round is enormous. The difficulties are multiplied a hundred-fold. It is no longer a simple operation, but a nice and complicated one. The part to be cast must first be oiled or soaped, then covered with plaster of about the consistency of rich cream, then divided into sections while the material is still tender, so as to enable the mould to be withdrawn part by part without breakage, then allowed to set, then removed, oiled or soaped on the interior surface, the parts all properly replaced, fluid plaster poured into the mould,—and finally, after the cast is set, the mould must be carefully removed by a hammer and chisel. This is an elaborate process as applied to an arm or a hand, but when applied to a living face it is not only difficult but disagreeable, and unless due care be used it may be dangerous; and after all a cast from the face is hard, forced, and unnatural in its character and impression, however skillfully it may be done, and can only serve the sculptor as the basis of his work. Yet if the common interpretation of the passage in Pliny be accurate, this is the process which was invented and practiced by Lysistratus, and by means of which he made portraits. _Credat Judæus!_ With all our knowledge and practice, we do not find this to answer in our own time. But to cast from a statue in clay is still more difficult and complicated; there the extremest care and nicety are required in making the proper divisions, in extracting the clay and irons, recommitting the sections, and breaking off the outer shell of the mould. In fact, the modern process is so complicated that no one can see it without wondering how it ever came to be so thought out and perfected, or without being convinced that it must have been slowly arrived at by many steps and many failures.