These are the only specimens, however, so far as we are aware, of any such use of plaster for low-relief ornaments,—the ectypa which have been preserved to us being invariably of baked clay. If plaster had been used for this purpose, we should expect to find casts in the interior of houses or tombs, where they would be protected from the weather, and where they could be easily introduced into the walls and ceilings. But though elaborately ornamented designs in relief, worked in gypsum, are to be found still fresh and uninjured on the ancient tombs and baths, all of them were freely and rapidly modeled by hand while the gypsum was still fresh and plastic, and not a single specimen of cast plaster has been found. It is but a few years since the tombs in the Via Latina were opened, and in two of them the ceilings, divided into compartments, were covered with rich and fantastic designs of flowers, fruit, arabesques, groups of imaginary animals, sea-nymphs, and human figures; the designs varying in each compartment, and all modeled in the plaster with remarkable vivacity and spirit: not one of them was cast. So in the houses at Pompeii, not a vestige of a figure or ornament cast in plaster has ever been found,—nor a mould in plaster; and when one considers that, being completely protected, they would naturally have survived as well as other far more fragile and destructible objects which have been preserved, the evidence is almost absolute that they never could have existed there. If so, it is in the highest degree probable that they existed nowhere. It would seem plain, then, that even the first, simplest, and most natural processes of casting in gypsum were unknown to the ancients, for no other process is so easy and simple as to fill a flat mould with plaster and then remove it, provided there are no under-cuttings. In doing this, however, there is a slight practical difficulty if the mould is in one piece, as the least under-cutting would render it impossible to remove the cast without injury or breakage. Indeed, though there were no under-cutting, it would at least be very difficult to remove the plaster from a mould in one piece. Clay would be removed with far greater ease because of its pliancy, and any cracks or imperfections could be at once remedied; add to this that baked clay is one of the most enduring of materials, and we have the probable reasons why the ancients used it instead of gypsum. But whatever may have been their reasons, it is perfectly clear that they did use clay; and we have no evidence that they ever used plaster.