Glass-painting is not only restored, in our day, to the perfect fullness of its ancient splendor, but also has acquired, through the giant strides of the science of chemistry, and the great progress latterly made in the arts of design, an amount of technical and aesthetical power far exceeding whatever could formerly be called to its aid.
Notwithstanding this advantage, however, the art has not yet reached that wide state of diffusion which, from the exquisite effects it is capable of producing, and deserves, and which it attained in the olden time, even with its then more limited capabilities.
The obstacles which, on the revival of the art, have interposed to check its further extension, and therefore to diminish also the general demand for its productions, are much rather to be attributed to those in whose hands it rests, than to anything properly belonging to itself; they originate in fact less in the art than with the artists.
One of the principal causes of the earlier decay of glass-painting was that its rules being based so entirely upon empirical principles, those who practised it were accustomed to consider the knowledge they had acquired in the thorny path of tedious and long continued experiment as their most valuable personal property, forming at once the means of their subsistence, and the foundation of their future artistical fame. They therefore not only kept the information they had gained profoundly secret during their lives, but even carried it with them to their graves, in preference to leaving it behind them to be made use of by their scholars.
Glass-painting or staining may be defined to mean the art of painting on transparent glass, (either colorless or already colored in the process of its manufacture), with vitrescible metallic colors, which are afterwards burnt into the surface of the glass on which they are laid, leaving it more or less transparent.
All colors used in glass-painting are oxides of metals, or other metallic combinations. They may be divided into two principal classes:
1. Those whose coloring base, or the oxide, is laid upon the glass simply in its original combination with an earthy vehicle.
2, Those whose coloring base, or the oxide, must be made to adhere by the help of a glassy body, namely, the flux.
The colors which require a flux may be divided again into,
1. Those in which the oxide unchanged, but only mixed with the flux, is attached to the glass.
2. Those in which the oxide requires to be vitrified, by previous fusion with the flux, before it is laid on the glass.
The last may be called fused colors, all others mixed colors.
The classification before given maybe made clearer by the following explanatory remarks. Glass-painting is distinguished especially from other illuminating processes in that the colors and the foundation on which they are laid must, in this art, be fused together in the kiln.
Now, some few colors combine with the surface of the glass, at the temperature of fusion, without further previous preparation than the simple laying on, wherefore these give to the glass only a coloring cementation or stain. Others, on the contrary, in consequence of their peculiar nature, can only be made to combine with the glass by fusing them upon its surface, into another thin sheet or layer of colored glass. This is done by means of the flux, a vitreous compound, which fuses more easily (i. e. at a lower temperature) than the foundation, the glass plate.
The Process of Laying the Colors on the Glass. The manipulation and the process of laying the colors on the glass varies, in some measure, according to the different kinds of glass-painting, which therefore call for the first explanation.
Either the colors may be laid upon a single sheet of glass, upon which the whole figure with all its principal colors and intermediate tints are burned in (Peinture en appręt): or,
The figure may be composed of various pieces of pot metal (glass already colored in its manufacture), and only the outlines and shadows painted on, the glass pieces giving the colors for the peculiar places where they are inserted (Mosaic glass-painting); or, both these methods may be combined in one and the same picture, by composing it partly of pieces of colored pot metal and partly of white and painted glass, fixed together,
Peinture et Appręt. For painting on a single sheet of glass, the following rules must be observed.
A pure white glass must be chosen for the purpose, free from air specks or bubbles, and especially difficult of fusion, as the whole labor would be lost if it were attempted to burn in the colors upon a ground which fused as easily as themselves. It is practicable, as the examples of the ancients show, to paint on what would appear the commonest glass with a good result, provided that it does not contain too much lead, and thereby become too easily fusible.
Before the operation of painting, the glass plate must be rubbed to a sufficient extent with pure lime, slaked by exposure to the air, in order to clean it perfectly.
The ground or foundation must then be laid over the whole surface of the plate, which may be done in two different ways. Some artists simply dip a piece of clean linen cloth, or a Hut camel-hail pencil, in oil of turpentine, and brush the pane of glass with it equally over its surface, while others give to the whole a thin clear ground of black glass-painting color, in such manner as not to destroy its transparency, but at most to give it the form of a dead ground glass. Both methods answer the purpose of covering the glass with a viscous surface, which takes the design and the colors better than a polished ground; the latter prepares the glass at the same time for the painting effects which are to be obtained upon it.