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 Æsthetical 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 may be 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 apprÊt); 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 ApprÊt. 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 flat camel-hair 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.

In both cases the ground which has been laid on must be most carefully leveled over, and brought to as thin a coat as possible with a large hair pencil, and must be dried quickly, taking great care to preserve it from dust, etc.

Painting on one sheet requires only one pattern drawing or cartoon, which, however, may be used in two ways. Either the glass sheet, grounded and dried as above directed, may be laid upon the drawing, and the outlines, as seen through the glass, traced lightly with a fine pencil, and with black or other glass color corresponding to the ground. Or the drawing may be placed reversed on the sheet, and all the outlines marked over with a steel or ivory style. If this latter method is used upon a ground of simple turpentine, the back of the drawing must previously be rubbed over with black lead, so that the traced lines may appear dark on the light ground.

In both cases, the drawing, whether it is placed upon or under the glass, must, for the sake of convenience, be fastened to it with pieces of wax at the four corners.

For properly carrying out the process of laying on the colors, a desk or easel is necessary, which should be capable of being placed in an inclined position by means of props, and should be formed by fixing a glass plate in a wooden frame, so that the light may pass through the painting. Sometimes during the progress of the work, the glass which is being painted may be removed from the easel and laid upon a sheet of white paper, in order better to show the effect of certain colors.

The vehicle with which the pigments are laid on is generally oil. Some artists use exclusively water, but this alone is an insufficient medium for binding the metallic bodies to the glass, particularly if, as in the case of fused colors, they are somewhat coarse in their nature, and require to be laid on in thick layers. They then easily loosen from the plate before the firing, and render the process of laying on much more difficult. It is an important advantage, that with oil the edges are more sharply defined, and the parts already painted may be again touched over when dry without danger of loosening the ground.

It must be understood that when it is wished to make use of water, the plate must either not be grounded at all, or only with a glass-painting color worked up with water.

The most suitable kind of oil for the purpose is rectified oil of turpentine, somewhat thickened by standing, and to which a little oil of lavender is added. This preparation gives the mass the necessary degree of viscosity, and also prevents the color on the palette from drying up and thickening too quickly.

The palette should be of thick sheet glass, ground rough by rubbing with a glass muller and fine sand.

Preparatory to mixing with oil for laying on, those colors which require a flux must (unless a different process is specially indicated) be ground fine in water with the flux, and again dried. But the fused colors, i. e. those in which the oxide has already been vitrified with the flux into the state of a transparent glass, should for the purpose of laying on, only be coarsely granulated; for the finer these are ground the more likely is their transparency and perfection to be impaired when burnt in.

Those pigments which are laid on in their simple combination with an earthy vehicle, and without flux, as for example the yellow and red colors prepared from silver, form an absolute exception to the use of oil, and must, for laying on, be stirred up with water to the consistency of a thick cream.

The first of these three kinds of pigments should, as a general rule, be laid on in a thin, the latter two in a pasty, state. The depth of tone of the color depends, with all three, upon the degree of thickness in which the pigments are laid upon the glass.

The laying on of the fused colors is accompanied with more difficulty than that of the other kinds. The latter are simply laid on with the pencil, in the same manner as with other kinds of painting, and the only care necessary is that the coat may be perfectly even and regular, therefore for large surfaces a wide smooth pencil or driver is usually employed. The colors prepared from silver must be treated differently, and laid on the glass at least to the thickness of the back of a knife.

But the fused colors must be brought upon the surfaces to be covered in the state of a thick flowing mass, moist enough to run, but consistent enough to lie upon the glass. For this purpose small portions must be laid on and spread out with a pencil or small spoon, and made to flow to the circumscribing outlines, by inclining the sheet in the proper directions. If any part of the surface thus covered is required to take a darker tone of color, the plate must be kept for some time at an inclination in the corresponding direction, so that the color may thus accumulate thicker on that part. By this process many gradations of tone may be obtained from one and the same pigment.

The remaining rules for the laying on of the pigments are those which principally result from the different methods of painting on one sheet, of which there are principally three.

Either the whole picture may be brought out in its outlines and shadows, on one side of the sheet, with black, brown or gray color, and illuminated with the proper colors in the proper places on the other side.

Or simply the manner of ordinary oil painting may be adopted with the glass colors, and the picture treated as by an artist in oil.

Or, as is now most customary, both methods may be united, the artist making use of each in certain places, according to the requirements of the object he has in view.

For these three methods the following common rules will serve.

The shadows and dark colored outlines, and that which is called in oil ‘under painting,’ should be drawn on the front side of the glass, or that which is turned towards the spectator.

The illuminating colors, especially the principal ones, should be laid on the back or reversed side.

Intermediate tints, and gradations by shading, should generally be placed on the front side, but sometimes, when they alternate with each other, necessarily must lie on both; as they cannot be put in contact on one and the same side without danger of running into each other, and making a false color.

The silver yellow and red colors, before alluded to, must always be placed on the back or reversed side.

In some particular cases colors may be laid on corresponding places on both sides of the glass, in order to produce certain effects by the light falling through the two together. Thus, purple on one side and gold yellow on the other, give a magnificent fiery scarlet; blue and yellow, according to their respective intensities, give different shades of green; the latter, again, with blue on the opposite side, serve for excellent distance colors. And finally, by the mixture of several colors, the most diversified intermediate tints may be obtained, so that glass-painting in its present state may be brought to assimilate with oil painting in its power of producing varied effects.

In order to put a new tone of color on a surface already marked with outlines, etc., it must first be dried by a gentle and equal heat, (to avoid the warping of the glass), and again painted immediately after it has cooled. Or the black lines first laid on may be at once burnt in, and where possible, with these any yellow shades also which may be required, after which the painting, then fixed, may be further worked upon without danger of damage. The residuum of the unfluxed yellow color may be removed after burning, and again used. This color must never be put over any other, nor over dark shadows, unless these are previously burnt in, but always require a carefully cleaned surface of glass to lie upon; otherwise it would combine with the flux of the under color, whereby the earthy residuum would be fixed, and the transparency and beauty of the whole destroyed.

All pigments must be laid on somewhat darker than in other kinds of painting, as they lose in depth by burning.

When a pigment has overrun its outline, the superfluous quantity must be removed, when dry, with a knife.

By taking away the ground with a style of fine grained wood, pointed in front and smooth at the back, (a tool used in etching), the most effective lights may be obtained.

Should the colors not appear quite dull and dry, but shining and greasy, after the drying of the picture, this is caused by the misuse of the oil, which is always dangerous to the beauty of the pigments in firing.

It is neither necessary nor advisable to allow more than one day for the drying of the colors; the burning in should be proceeded with at the expiration of the time named.

Lastly, during the work, the greatest cleanliness must be observed throughout, the pencil and palette must be kept perfectly clean, and the painting preserved from dust, etc., for which reason it is not advisable to paint in a laboratory or melting room, where the presence of vapor, dust, and impurities of many kinds cannot be avoided.

Mosaic Glass-Painting. The before mentioned rules for laying on the colors will apply also to the method of forming designs with colored pieces of pot metal, or partly with these and partly with painted white glass. It remains to say something more in reference to the employment of the cartoons, and the cutting and arrangement of the glasses in this branch of the art, which, however, is but little practiced, since the leaden bars in a picture calculated for a near view are detrimental to the effect.