# Cyclopedia of Painting/Oil Painting on Glass

OIL PAINTING ON GLASS.
There are three principal modes of oil-painting on glass, as follows:
Non-Transparent Painting on Transparent Glass. In this mode the materials are the same, and the method the same, except in one particular, as that employed in painting on the front of mirrors. The sole particular in which it differs from this kind of mirror painting is this: it must be much less transparent in the shadows and half tints, for the reason that it has no silver foil or ground; the paint, therefore, must have sufficient body in every part to prevent anything dark or bright behind from being visible through it, and thus affecting the coloring. This mode is much used for decorating unsilvered plates of glass to be inserted as panels in screens. As, however, the back of the screen is not covered in the usual way, if both sides are likely to be seen, and it be found desirable to hide the unpleasant appearance of the back of the painting, this can only be done by repainting on the back of the glass the subject on the front.
The outlines must be made to coincide with those showing through and a study of the subject should be used to fill in within the outlines, but less finish will usually suffice.
Transparent Painting on Transparent Glass. This kind of painting is applied to windows, magic-lantern slides, etc.
Mirror-Painting on the Back of the Glass. This style of painting may be done either before or after the silvering. The former is the usual course, because simpler and less toilsome. In this case it is of the first imports nee that the outlines, or rather the boundaries, should be rendered sharp and true and with a good body of color, otherwise their ragged or blurred edges will be emphasized by the subsequent silvering.
​The chief difficulty in painting on the back of the glass is to calculate the effect each touch will have when viewed in front. On so viewing his touches the artist will often be surprised at the discordancy they present, though he may have calculated their relative effect very carefully. There is no expedient that will materially lessen this difficulty. All that can be done is to register, so to speak, the value of the transparent, and the solidity of the opaque couches of paint, by placing a sheet of white paper behind the former, and a sheet of black paper behind the latter.
The colors that are more or less transparent must be applied at the outset, but they will only appear as such and of their proper tint and hue when opaque paint is spread over them. Of course, the transparent colors must not be reserved for final glazing, the whole process of ordinary painting being reversed, the last strokes of the latter having to be the first strokes of painting on the back of a mirror.
As the face of the paint must be as smooth as the polished surface to which it clings, texture, for the representation of the surfaces of objects, can only be obtained by means less direct, for the most part, than those available for other applications of oil-painting. When using transparent colors, and texture be required, they must be applied in a broken manner, and when using opaque colors for the same purpose they should be spread thinly, then scraped, and other tints or hues passed over them so as to show between the interstices of the scraping, according to the requirements.
When the work is otherwise complete a solid coat of white should be spread over the whole, and when this is dry a thick coat of Brunswick black. The first will prevent the second from showing through, as it might to the great detriment of the coloring. Brunswick black is used as the overcoat, because it effectually protects the painting proper from injury by the subsequent silvering.
​If the plale is already silvered a separate study should be made and the outlines of this study traced on the back of the silvering. This being done, the portion of the silvering that the painting must occupy is etched away by a scalpel or other sharp blade, taking care not to scratch the glass. The etching may be effected and outlines obtained without much trouble if the silvering has been done by the mercurial process. But it is not so with the modern silvering, this being covered with a coat of hard varnish-paint that is almost impossible to remove without leaving ragged edges. Only for a large plate to be viewed at a distance should it be attempted, and then, so great is the labor involved, it would generally prove more economical to exchange the plate for a new one unsilvered.
All painting on the back of mirrors has, however, inevitable defects, which are apt to prove somewhat antipathetic to artists. Its difficulties, while augmenting the cost to the purchaser, preclude commensurate results. For the reason that the painter cannot see the progress of his work with the usual facility, the coloring can hardly be very harmonious. To mix each first touch of paint to the required hue or tint and lay it on at once in the right place is not easy to an experienced artist, but the difficulty is enormously increased when the work has to be turned to ascertain how the last touch behaves relatively to all those which preceded it. The coloring must also be comparatively dead, owing to the opaque ground. The painting can hardly appear other than flat and monotonously smooth, or with little spirit of handling, or touch, descriptive of texture and expression of light. And, although by this method there are no reflections from edges of the painting when the mirror is viewed at an angle, yet the painting is obscured by reflections from the surface of the glass before it, as well as lowered in brilliancy by the thickness and any greenness of the glass.