Nearly all American moulders (as distinguished from French and Italian ones) varnish the mould, and thus lose some of the finest detail and sharpness. This is unnecessary. The mould can be easily prepared with a solution of soap so as to leave nothing on the surface but a very thin coating of oil, which is taken up and replaced by the plaster of the cast. Of course, if the model has been sand-papered, no fine work in moulding or casting is necessary, as there is nothing to save. If the subject is a very intricate one, with "undercuts" (as they are called), it is customary to make a waste mould; as this is very seldom necessary in relief map work, however, the process need not be described. To make the cast it is only necessary to repeat the processes used in making the mould. With great care and some skill a cast can be produced but little inferior in point of sharpness and detail to the original model. It is customary to make the cast very thick, and, consequently, very heavy; this is unnecessary. In our work we seldom make a cast thicker than one inch, and yet are never troubled with changes in the model after it is finished. Even in a very large cast (now in the National Museum), weighing nearly 1,500 pounds and presenting a surface of over 160 square feet, the average thickness is less than one inch, although it required over five barrels of plaster to make it. The cast, after being thoroughly dried, should be finished--all its imperfections being carefully repaired. The surface, however, should be touched as little as possible, as the slight roughness of surface that comes from the original model, through the mould, is removed by any tooling. This roughness adds much to the effect of the model; in fact, where the scale is large enough, it is sometimes desirable to emphasize it.