Glass Painting ,.The art of painting upon glass is supposed to be of Byzantine origin, and to have arisen since the beginning of the Christian era. The first authentic account of the subject is given in the Diversarum Artium Schedule, a work written by Theophilus, probably in the 12th century, though by some authorities its date is assigned to the 10th. The complete description given in this treatise of the process of painting on glass justifies the conclusion that the art itself must have been invented at a much earlier period; but the oldest specimens now existing do not date further back than the beginning of the 11th century. Indeed, the oldest existing specimens to which a date can with certainty be assigned has been considered by M. de Lasteyrie and other French antiquaries to be the windows in the cathedrals at Angers and St. Denis, which were painted about the middle of the 12th century. The skill of the French painters on glass was extolled by Theophilus, and to the present time France has continued to be the richest storehouse of painted glass of the earliest style. The process described by Theophilus continued to be practised until about the middle of the 16th century, when the art reached its zenith.

The most eminent painters practised it, as Albert Durer, Bernard Palissy, and others, and their works are still admired in the churches of that period, as the Cologne cathedral, York minster, and many others. But in the next century the art had entirely declined, for the reason, as Labarte suggests in his "Illustrated Handbook," that its intention was perverted in the transformation of an art of purely monumental decoration into an art of expression. For this oil painting possessed greater resources, and glass painting necessarily fell into neglect. In some modern attempts it is remarked that the primary object of the glass in transmitting light appears to be overlooked and sacrificed in the opaque shadows introduced. In the ancient glass pictures the figures were formed of pieces of stained glass, and the shadows were laid on with dark colors and fixed in the fire. Intense colors were exclusively employed, the ruby and blue always predominant. The ground was mosaic in circles, squares, and lozenges, of massive forms, and filled with foliated ornaments in the Roman style. Over this were medallions representing historical and biographical subjects from the lives of the saints.

When figures came to be introduced, they were generally grotesque and distorted; but the costumes were remarkably correct. The designs always harmonized with the style of architecture, stately and magnificent in the Norman structures, and light and elegant in those of the early English models in the 18th century. In these the brilliant positive colors were made more subsidiary, appearing in borders, geometric bands, and central points, while the ground was of a neutral gray produced by lines crossing each other at right angles. The designs were also more correctly drawn, and shaded with greater delicacy. For the violet tint always before used for the faces of the figures was substituted a gray or brown upon colorless glass. The pieces of glass were of larger size, and a single figure was often made to occupy a whole window, standing beneath an elaborate blue or red canopy. In the background, among the architectural fragmentary designs, still appeared the old Poman foliated ornaments, but intermixed with original studies from nature, a style of the art which was afterward carried to great perfection. Not only leaves, plants, and trees, but even landscapes and buildings in perspective, appeared in the latter half of the 15th century.

The Scripture pieces were often explained by legends painted upon the phylacteries, and in the background were represented rich blue or red hangings of damask. - After along decline, the 19th century has witnessed a revival in the art of painting on glass, which is now extensively practised in France, Germany, and England, the finest specimens being produced at Munich. In earlier periods it was devoted chiefly to ornamenting cathedral windows with sacred illustrations, but it is now used for general purposes of ornamentation, embracing a wide range of secular subjects. The belief in the superiority of ancient glass painting, which was even regarded by some as one of the lost arts, has been superseded by the opinion held by the highest authorities that painted glass can now be manufactured superior to the best specimens of the middle ages. Indeed, the processes then in use have been brought to light by modern research. In 1850 a series of chemical analyses was instituted by Mr. C. Winston of England, who during his life made the subject of painted glass in its antiquarian aspects a special study, and the earliest specimens were carefully analyzed.

The results reached made it easy to reproduce both the quality and the color of the ancient glass. - Glass painting, which is more properly a process of staining, differs from all other styles of pictorial art, except the painting of porcelain. The colors are different, being wholly of mineral composition, and are not merely laid on the outside, but fixed by being fused into the material, undergoing in the operation chemical changes that develop the brilliancy and transparency of which the compounds are susceptible. The colors are mixed with a flux of much easier fusion than the glass, and with some vehicle, as boiled oil or spirits of turpentine. The mixture is usually laid on with a brush as in ordinary painting; and the glass being then exposed to heat, the flux melts and sinks into the body. None of the clear bright colors are perceived until the work is completed, and the artist consequently labors under great disadvantage in applying the materials that are to produce them. He is guided either by lines drawn on the back side, which show through, or by a cartoon or drawing on paper placed there. In the early use of glass for windows, especially those of churches, brilliant colors were highly esteemed, and great success was attained in the methods of coloring.

A bright red color was imparted by the ancients with the protoxide of copper. In later times it was found impracticable to succeed with this on account of the tendency of the copper to pass to a peroxide and produce a green tinge; but the practice has been again introduced with success by the Tyne company in England, at Choisy in France, and in other places. The discovery of the preparation of gold and tin, called purple of Cassius, also afforded another means of producing a brilliant red. - In the history of the art two leading processes have been prominent. From the earliest period until about the middle of the 10th century the method described by The-ophilus and known as the mosaic system prevailed. In this process the glass was colored in the manufacture, and blocks of different colors having been brought together, the outlines and shading of the design were produced by the application of an enamel color. About the time mentioned it was discovered that all colors besides yellow, brown, and light red, which had previously been imparted by this method, could be given to glass by means of the enamel process; but the works produced by this method were greatly inferior to those by the mosaic system.

There has been a spirited controversy between the advocates of the German method of glass painting, in which enamel is used, and the English glass painters, who avoid the use of enamel as far as possible, as it sometimes scales off. It seems to be conceded that the beauty of the cathedral glass of the 13th and 14th centuries was in the brilliancy of the glass and the skilful arrangement of designs and colors, and not in any enamel work. The ordinary method of glass painting, as practised in England, is to use for the colored parts of the design pieces of glass differently colored in the process of manufacture, and to employ only one enamel color, brown, for tracing the outlines and painting the shadows of the picture upon the glass. The enamel brown, like any other enamel color, consists of coloring matter mixed with pulverized glass, called flux or enamel. When this is laid on the surface of the glass and heated in an oven or furnace, it melts, in consequence of being more fusible, while the glass is merely at a red heat; on being cooled it hardens and produces a permanent color on the surface of the glass. The general colors of the design, therefore, are not produced by the painter, but by the glass maker; the former, as has been stated, using pieces of glass already colored.

The only exception to this is in the case of yellow, which is produced on the glass by applying a "stain," the principal ingredient of which is oxide or chloride of silver. On being exposed to the action of a red heat, the yellow stain penetrates the glass and imparts to it its tint, the preparation of silver being afterward brushed off. This process was discovered in the early part of the 14th century, and has been used to impart a yellow tint to uncolored and most kinds of colored glass. The various tints of yellow are the only ones that can be produced on glass without altering its surface. By putting on a second or third coating of the silver oxide and burning in, orange and red stained glasses are produced. - The process of producing a painted glass window is an interesting one. The artist first makes an outline on a small scale of the stone work of the window, within which he sketches the design, indicating the colors to be used and the general treatment of the subject. A full-sized drawing or cartoon is next made, from which a "cutting drawing" is traced, showing the lines where the strips of lead are to go, and omitting all other details.

On this latter drawing, on which the colors of the design are indicated by outlines, the pieces of different colored glass are laid and cut with a diamond, each piece being cut out of that particular color or tint required. The artist now arranges the pieces of different colors in their proper places on the cartoon, and traces the outline of the design upon them. On being heated in an oven, the opaque lines vitrify and are formed indelibly on the surface of the glass. After the outlines have been thus "burnt" on, the glass is taken again to the painter, who covers the cartoon with a sheet of colorless glass, or if large a portion of it at a time. Thus having the cartoon for a guide, he arranges in their proper places on the sheet of colorless glass the pieces on which ! the outlines have been traced, and secures them firmly with drops of melted resin and beeswax, or other suitable substance. The sheet of colorless glass, with the pieces thus arranged adhering to it, is placed upon an easel, and the shadows of the picture are put on with the same material as that used in tracing the outlines. The shading, however, is not traced from the cartoon, as were the outlines, but is done by the skill and experience of the painter.

When the shading is completed, and the tints of yellow, if any are required, are put on, the pieces of glass are detached from the colorless sheet and again subjected to heat, for the purpose of "burning in" the shadows. If more work by the painter is required, the process is repeated, the glass being thus subjected to heat in some instances six or seven times. The work of the painter being completed, the finished pieces are taken by the "leader," who, having arranged them by the aid of the "cutting drawing" so as to form the entire design, fastens them together by means of strips of grooved lead skilfully fitted around the edges of the several pieces. If the window is a large one, as is generally the case, it is divided into parts of convenient size, which are fitted together when the window is put in its place. Bars of iron are also sometimes placed across the window at the line of junction and at other convenient intervals. This general process of producing mosaic stained glass windows has been in use from the earliest times, though it may have been modified in some of its details; and until some other method of imparting colors to glass without detracting from its transparency and brilliancy is discovered, the opaque lead lines in the design must be accepted as a necessity.

In his "Art of Glass Painting," Mr. 0. Winston says: "The necessity of leading a glass painting together is one of those conditions which cannot be evaded by any ingenuity. The lead work and saddle bars must be accepted as necessary parts of the composition. The design must be made with reference to them, and that glass painting must be acknowledged to be the best which admits of the leads being thrown into the outlines, and made to serve as outlines; and which by the simplicity, I might almost say roughness, of its design and execution, prevents the harshness of the saddle bars from being obtrusive. In this respect the glass paintings prior to 1550, and until the 18th century, must be considered superior to those later works in which the attempt has been made to ignore the leads and saddle bars, by leading the work together in squares independently of the outlines of the composition, or by twisting the saddle bars so as to avoid their cutting the design at regular intervals; because both methods immediately suggest the idea of a blemished picture, and make us immediately perceive how much better the work would be without leads or saddle bars.

But a window cannot be constructed without them; hence it is better to adopt; them as essential parts of the design; and the beautiful windows of the choir of this [Lichfield] cathedral, which bear date between 1532 and 1539, show that a design so constituted is compatible with high pictorial effect." Another condition which must be particularly observed is the preservation of transparency in the highest degree consistent with the production of a picture. For this purpose the high lights of the window must be as free from shading as possible. Indeed, light shading throughout the entire design is one of the conditions imposed by the nature of the material. These conditions were fully recognized by the artists of the middle of the 16th century, and this fact accounts largely for the superiority of their productions to those of their predecessors. In the best glass paintings of that period there is always an abundance of light in the upper portion of the window, while in the choice of subjects and their general treatment the artist selected those that could be made the most effective with the least shading. - Among numerous works on this subject are: Lasteyrie, Histoire de la peinture sur verre d'apres des monumens en France (2 vols., Paris, 1838-'56); Gessert, Geschichte der Glasmalerei (Stuttgart, 1839); Ballantine, "Treatise on Painted Glass " (London and Edinburgh, 1845); Bontemps, Peinture sur verre au dix-neu-vieme Siecle (Paris, 1845); Weale, "Ancient Painted and Stained Glass" (London, 1846); Winston, " Inquiry into the Difference of Style observable in Ancient Glass Paintings, especially in England, with Hints on Glass Painting" (London, 1847), and "An Introduction to the Study of Painted Glass " (Oxford, 1849); Warrington, " History of Stained Glass " (London, 1848); Fromberg, "An Essay on the Art of Painting on Glass" (London, 1851); Bielfeld, " A Guide to Painting on Glass " (London, 1856); and Winston, "Memoirs illustrative of the Art of Glass Painting" (1865).