Scientific American. Volume 3, numero 8, s. 64
It is a singular fact, that the art of glass-painting, practised with such success during the former ages from one end of Europe to the other, should gradually have fallen in such disuse. In the beginning of the last century it came to be generally considered as a lost art. In the course of the eighteenth century, however, the art again began to attract attention and many attemps were made to revive it. It was soon found by a modern artists, that by employing the the processes always in use among enamel painters, the works of the old painters on glass might in most respects be successfully imitated; but they were totally unable to produce any imitation whatever of that glowing red which sheds such incomparable brilliancy over the ancient windons that still adorn so many of the churches in Europe.
For this spendid color they possessed no substitute, until a property, peculiar to silver alone among all the metals, was discovered, which will presently be described.
The art of enamelling on glass differs little from the well known art of enamelling on other substances. The coloring materials, which are exclusively metallic, are prepared by being ground up with a flux, that is, a very fusible glass composed of silex, flint glass, lead and borax; the color with its flux is then mixed with a volatile oil, and put on with the brush. The pane of glass thus enamelled is then exposed to a dull red heat, just sufficient to soften and unite together the particles of the flux by which means, the color is perfectly fixed on the glass.
Treated in this way, gold yields a purple; gold and silver mixed, rose color; iron brick red, cobalt and blue; mixtures of iron, copper and manganese, brown and black. Copper which yields the green in common enamel painting, is not found to produce a finer color when applied the name way to glass, and viewed by transmitted light ; fora green therefore, recourse is often had to a glass colored blue on one side and yellow on the other.
To obtain a yellow, silver is employed, which either in the metallic or any other form, possesses the singular property of imparting a transparent stain when exposed to a low red heat in contact with glass. This stain is either yellow, orange or red, according to circumstances. For this purpose no flux is used; the prepared silver is merely ground up with ochre or clay, and applied in a thick layer on the glass.
When removed from the furnace the silver is found not at all adhering to the glass; it is easily scraped off leaving a transarent stain: which penetrates to a certain depth. If a large proportion of ochre has been employed, the stain is yellow: if a small proportion, it is orange colored, and by repeated exposure to the fire without any additional coloring matter, the orange may be converted into red. This conversion of orange into red is, we believe a matter of much nicety, in which experience only ensure success. Till within a few years this was the only bright red in use among modern glass painters; and though the best specimens certainly produce a fine effect, yet it will seldom bear comparison with the red employed in such profusion by the old artists.
Besides the enamels and stains above described, artists, whenever the subject will allow of it, make a of panes throughout their substance in the glass-house melting pot, because the perfect transparency of suvh glass gives a brilliancy of effect, which enamel-coloring, always moreor less opawue, cannot wual. It was to a glass of this kind that the old glass painters owed their splendid red.— This, in fact, however, is the only point in which the modern and ancient processes diffee, and this is the only part of art which was really lost. Instead of blowing plates of solid red the old glaze-makers used to flash a thin layer of red over a substratum of plain glass.
(To be Concluded.)