In October, 1859, a patent was granted to James Napier, of Glasgow, Scotland, for a very simple method of ornamenting glass with fluoric acid. Instead of drawing patterns and figures on the glass with the use of varnish and a graver to prepare the glass for etching, the glass is prepared by simply transferring pictures from prints, which can be performed by almost any person. The method is, to take a print, lithograph, or picture made with printer's ink, and fix the printed surface to the glass by any ordinary paste made from starch. All the air must be carefully excluded from between the print and glass. When perfectly dry, liquid hydrofluoric acid about the specific gravity of 1.14 is applied for about three minutes, when it is washed in water to remove the paper and the acid, and the figure of the print is then found upon the glass. The printed portion of the paper may also be cut in outline and pasted on the glass, then transferred. Glass that is "flashed" on the surface with another color may be treated in this manner, when a portion of the flashing or surface will be removed, and the picture will remain in color.
The distinguished French chemist, M. Chevreul, who has devoted so much attention to the subject of color, has lately published a memoir on painted windows, in which there are many points which deserve the attention of artists and others who are interested in the manufacture of colored glass. It has often been much noticed that old stained glass windows have a much richer effect than modern ones, and M. Chevreul, speaking of this superiority, attributes it to what moderns regard as defects. In the first place, much of the ancient glass is of unequal thickness, and so presents convex and concave parts, which refract the light differently and produce an agreeable effect. In the next place the old colored glass is not a colorless glass, to which has been added the particular coloring material, such as protoxide of cobalt, &c. Old glass contains a good deal of oxide of iron, which colors it green, and to this must be attributed the peculiar effects of antique glass, colored by cobalt and manganese. M. Chevreul appears to think that modern stained glass is too transparent to produce the best effects. M. Regnault, the chemist, has recommended that all this kind of stained glass should be cast, to avoid the monotonous effect of plain surfaces on the light; and also that foreign substances should be mixed with the glass to diminish its transparency.