extent, also, on the use to which the model is to be put. The plain cast is sometimes used, drainage, lettering, etc., being put directly upon it. This has the advantage of preserving all the detail that comes from the mould, but it has also the disadvantage of a surface easily soiled and impossible to clean. If the model is to be photographed, the surface should be nearly white—in our practice we use a small amount of yellow with the white. This yellow is hardly appreciable by the eye, but its effect upon the photographic negative is quite marked. Yellow becomes grey in a photograph, and, in a photograph of a model colored as described, a grey tint is given to the whole surface. The high lights are not pure white, and there is no harsh contrast between light and shade. There is another point of great importance in photographing models: the surface should have a dead finish—that is, should have no gloss, or, at most, should have only what is known among painters as an egg-shell gloss. It is almost impossible satisfactorily to photograph a model that has a shiny surface. Any portion of a model that it is desired to separate from the rest should be painted a different color—the water, for example, should be painted a light blue; not a blue composed of indigo, however, or any of the grey blues, as these produce in the photograph a dead grey, and are not pleasant to the eye. The most satisfactory color that we have used is a mixture of cobalt—the purest of the blues—with Antwerp blue—which is quite green—and white. This gives a color that is pleasant to the eye, has the retreating quality to perfection, and photographs well.
Models intended for exhibition as such should be painted realistically. There is room here for an immense improvement in the usual practice, which is to paint the model either in some conventional scheme of light and shade, or else to put a single flat tint upon it. If the model is to be colored conventionally it is, in my opinion, much better to use a flat tint, light in tone, and with a dead surface. The use of a variety of colors upon the face of a model interferes materially with the relief, especially if the relief is finely modeled. For this reason models colored to indicate geologic formations should always be accompanied by duplicates representing topography only, colored realistically, if possible, and without lettering. Well-defined lines other than those pertaining to the model itself, such, for example, as those used to define the boundaries of geologic formations, should not
