For one ounce of red chalk pounded, and mix it with two ounces of white hard enamel, and a small proportion olthe scales of copper which fall off when it is much heated b.1 a forge. This will make a very good red, but requires trril if it will support the fire; and if not, add more of the scaes of copper.
For another ret.—Take one part of red chalk, which is too hard to write with, one part of white enamel, and a fourth of orpimetr; grind them together with vinegar. This is a strong poixin.
Or a red may be cemposed of rust of iron, glass of an timony, and yellow grass of lead, such as is used by pot ters, these three in equal quantities; to which add a little silver, calcined with sulphur. This composition, ground fine, produces a very fine red colour on glass.
When the oxide of copper is used to stain glass, it as sumes a bright red or a green colour, according as the glass is more or less heated in a furnace.
Bistres and brown reds may be obtained, by mixtures of different proportions of manganese, brown oxide of cop per, and the oxide of iron called umber. They are pre viously fused with their solvents.
For green.—Take two ounces of brass burned until it becomes a calx, two ounces of minium, and eight ounces of fine white sand; reduce them to a fine powder, which inclose in a well luted crucible, heated in an air furnace with a strong fire for an hour. When this mixture is cold, pound and grind it in a brass mortar. Green may often be advantageously obtained, by a yellow on one aide, and a pale blue on the other.
For a fine yellow colour.—Take fine silver in thin plates, and dissolve it in nitrous acid, and precipitate it ; mix the precipitate with three times the quantity of pipe-clay, well burnt, and pounded. With this the back of the glass must be painted, or it will run into the other colours.
Another yellow can be made by melting silver in a cru cible, and whilst in a state of fusion throw into it powdei ecl sulphur in small quantities, and stir it up until the sil ver is reduced to a calx. Grind this upon a stone, and mix with it as much antimony as the silver, and some yel low ochre, which has been previously calcined in a cruci ble, until it is changed to a red brown colour. Work all
these together with urine, and paint it on the back of the glass.
Another yellow.—Cut thin plates of silver into small pieces, and put them into a crucible with sulphur and an timony. When melted, throw out the contents into clear water, and afterwards pound and grind the preparation, so that it will work with a pencil.
A pale yellow.—Fill a crucible with thin plates of brass, with beds of sulphur and antimony in powder. Burn it till it ceases to smoke, and throw it hot into water. Re duce this to fine powder, and having added six times as much yellow ochre burnt, mix it with vinegar.
A fine yellow, equal in beauty to that of the ancient pain ters, has been discovered by M. Meraud. He employs muriate of silver, oxide of zinc, white clay, and the yel low oxide of iron. These colours are applied to the glass simply ground, and without flux.
Blue colour.—Take mountain blue, and beads of glass, equal portions ; grind them whilst dry to an impalpable powder, and proceed as with the others.
In general, the same colours as are used for painting on porcelain, and many of those used in enamel painting, may be employed with success upon glass. But after all, the painter must employ no colour without making trial of it upon the slips of glass. The colours in general become more faint by longer continuance in the fire, because they sink deeper into the glass. But every preparation varies in this respect. All the colours are mixed up for the pen cil with gum water in sufficient quantity to make them work properly.
A number of very interesting experiments on the colours obtained from metallic oxides, and fixed by means of fusion either on porcelain or glass, have been made by M. Brong niart, director of the royal porcelain manufactory at Sevres. In the preceding list, we have already given some of his results ; hut in our article PORCELAIN, which that celebra ted mineralogist has undertaken to furnish for this work, our readers may expect the fullest and most recent infor. mation on the subject.
A plate of glasss may be cut into any shape, either by the diamond, or by a bar of red hot iron.