STAINED GLASS 881 



such as is used by potters (or litharge), each in little quantity ; to which a little sul- 

 phuret of silver is added. This composition well ground, produces a very fine red 

 colour on glass. When protoxide of copper is used to stain glass, it assumes a bright 

 red or green colour, according as the glass is more or less heated in the furnace, tho 

 former corresponding to the suboxide, the latter having the copper in the state of 

 protoxide. 



Bistres and Brown reds may be obtained by mixtures of manganese, orange oxide 

 of copper, and the oxide of iron called umber, in different proportions. They must 

 be previously fused with vitreous solvents. 



Green colour. Two ounces of brass calcined into an oxide, two ounces of minium, 

 and eight ounces of white sand ; reduce them to a fine powder, which is to be enclosed 

 in a well-luted crucible, and heated strongly in an air-furnace for an hour. When the 

 mixture is cold, grind it in a brass mortar. Green may, however, be advantageously 

 produced by a yellow on one side, and a blue on the other. Oxide of chrome has 

 been also employed to stain glass green. 



A. fine Yellow colour. Take fine silver laminated thin, dissolve in nitric acid, dilute 

 with abundance of water, and precipitate with solution of sea-salt. Mix this chloride 

 of silver, in a dry powder, with three times its weight of pipe-clay well burnt and 

 pounded. The back of the glass-pane is to be painted with this powder, for when 

 painted on the face, it is apt to run into the other colours. 



Another yellow can be made by mixing sulphide of silver with glass of antimony, 

 and yellow ochre previously calcined to a red-brown tint. Work all these powders 

 together, and paint on the back of the glass. Or silver laminae melted with "sulphur 

 and glass of antimony, thrown into cold water, and afterwards ground to powder, 

 afford a yellow. 



A pale yellow may be made with the powder resulting from brass, sulphur, and glass 

 of antimony, calcined together in a crucible till they cease to smoke ; and then mixed 

 with a little burnt yellow ochre. 



The fine yellow of M. Merand, is prepared from chloride of silver, oxide of zinc, 

 white-clay, and rust of iron. This mixture, simply ground, is applied on the glass. 



Orange colour. Take 1 part of silver powder, as precipitated from the nitrate of 

 that metal by plates of copper, and washed ; mix it with 1 part of red ochre and 1 of 

 yellow, by careful trituration ; grind into a thin pap with oil of turpentine or lavender, 

 and apply this with a brush, dry, and burn in. 



In the Philosophical Magazine, of December 1836, the anonymous author of an 

 ingenious essay, ' On the Art of Glass-painting,' says, that if a large proportion of 

 ochre has been employed with the silver, the stain is yellow ; if a small proportion, it 

 is orange-coloured ; and by repeated exposure to the fire, without any additional 

 colouring-matter, the orange may be converted into red ; but this conversion requires 

 a nice management of the heat. Artists often make use of panes coloured throughout 

 their substance in the glass-house pots, because the perfect transparency of such glass 

 gives a brilliancy of effect, which enamel painting, always more or less opaque, cannot 

 rival. It was to a glass of this kind that the old glass-painters owed their splendid 

 red. This is, in fact, the only point in which the modern and ancient processes differ ; 

 and this is the only part of the art which was ever really lost. Instead of blowing 

 plates of solid red, the old glass-makers (like those of Bohemia for some time back), 

 used to flash a thin layer of brilliant red over a substratum of colourless glass ; by 

 gathering a lump of the latter upon the end of their iron rod in one pot, covering witli 

 a layer of the former in another pot, then blowing out the two together into a globe 

 or cylinder, to be opened into circular tables, or into rectangular plates. The elegant 

 art of tinging glass red by oxide of copper, and flashing it on common crown glass, 

 has become general within these few years. 



That gold melted with flint-glass stains it purple was originally discovered and 

 practised as a profitable secret by Kunckel. Gold has been recently used at Birming- 

 ham for giving a beautiful rose-colour to scent-bottles. The proportion of gold should 

 be very small, and the heat very great, to produce a good effect. The glass must 

 contain either the oxide of lead, bismuth, zinc, or antimony ; for crown glass will take 

 no colour from gold. Glass combined with this metal, when removed from the cru- 

 cible, is generally of a pale rose colour nay, sometimes is as colourless as water, and 

 does not assume its ruby colour till it has been exposed to a low red heat, either under 

 a, muffle, or at the lamp. This operation must be nicely regulated ; because a slight 

 excess of fire destroys the colour, leaving the glass of a dingy brown, but with a green 

 transparency like that of gold-leaf. It is metallic gold which gives the colour ; and, 

 indeed, the oxide is too easily reduced, not to be converted into the metal by the 

 intense heat which is necessarily required. 



Coloured transparent glass is applied as enamel in silver and gold bijouterie pre- 

 viously bright-cut in the metal with the graver or rose-engine. The cuts, reflecting 

 VOL. III. 3 L 



