Procured by dissolving gold in aqua regia (nitro muriatic acid) and immersing a bar of pure tin therein. This is called the " purple precipitate of Cassius."
Prepared with fulminating gold (made by dissolving the metal with aqua regia and precipitating with ammonia) and muriate of silver.
These colours are dull when laid on, but after exposure to the heat of the oven, they are developed in brilliant tints.
Red oxide of iron, prepared by the united action of fire, and nitric acid.
Mixture of proportions of black and red oxides of iron.
By calcining the oxide of iron with double its own weight of chloride of sodium.
The salt must be carefully decrepitated, i.e. heated until all crackling noises cease.
The oxide is procured by dissolving iron filings in nitric acid, and precipitating with salt of tartar (sub-carbonate of potass).
The precipitate is then placed on a thin iron sheet, and exposed to the heat of a charcoal fire, under a muffle, until it assumes a fine tint.
The two substances having been well triturated together in a glass or porcelain mortar, are transferred to a crucible, where they are calcined, which must be done without vitrifying the mass.
When taken and cooled, the compound is again triturated; portions of hot water are now successively poured upon it, and then removed, till the water is no longer coloured. The fluid thus tinted is allowed to settle, and when clear, it is poured off and the sediment is carefully washed several times in clear water.
White oxide of antimony, mixed with sand and oxide of lead. The latter is used as a flux.
Oxide of tin is sometimes added.
Add to the above red oxide of iron.
Oxide of uranium mixed with oxide of lead. Decomposed chromate of potass, with nitrate of lead, which is a saturated solution of lead in nitric acid. Chromate of lead is precipitated.
Twenty-four parts of ceruse, four parts of oxide of antimony, and one part each of alum and sal ammoniac (muriate of ammonia) calcined at a moderate heat for three hours.
Sal ammoniac varies the shades.
The quantity of flux to be used in combination is uncertain, and must always be a matter of experiment.
Very pure, and well prepared oxide of cobalt, mixed with a flux. Oxides of tin and of zinc added, give shades from deep, to light azure.
Smalt or Azure Blue. Glass of cobalt mixed with sand, fused in a crucible and reduced to an impalpable powder in an agate mortar; after which it may be used in combination with flux.
A union of hydrocyanic acid with -oxide of iron.
Green oxide of copper. Pure and concentrated solutions of copper precipitated by means of potass in various vessels, form in the latter various diversities of tint.
A mixture of oxide of cobalt and nickel.
Oxide of chromium.
Oxides of iron. Various tints are thus produced. The flux used is felspar.
Oxide of Manganese. An inferior tint is made with black oxide of iron.
Another—compound " oxide of manganese, oxide of (brown) copper, and a small portion of oxide of cobalt."
As above, omitting the copper.
One part of virgin tin and two parts of common salt, thoroughly purified by dissolving the latter in distilled water, filtering it through paper, and then evaporating it over a fire in a porcelain capsule, and heating it in a crucible until all decrepitation ceases. The purification will be more perfect, by filtering the solution, evaporating it, and then leaving it in a cool place to crystallize.
Preference is given to cube shaped crystals.
Next, place a crucible (well covered to keep out smoke, etc.) on the fire. When red hot introduce the tin, and leave it until it is not only fused, but red hot. Then add the purified salt.
Take then a clean iron spatula, the end of which must be hot, and stir the substances together.
The crucible is again covered and surrounded with burning charcoal, and from time to time the contents must be stirred. This process occupies an hour.
Next bruise the compound in a glass or agate mortar, and again put it in a crucible, covered with a muffle, in burning charcoal.
Then for three hours gradually raise the heat, until on removing the crucible, the colour requires some force, to detach it from the sides.
Again pound it in a mortar and wash it in distilled hot water, with portions of fresh water added, till all taste of salt disappears. Then boil violently, the white colour, with an abundance of water, in an earthen jar, replacing the water that evaporates, for two hours. Then pour off the water, and the process is complete.
Red lead..................... 8 parts
Oxide of antimony ...... 1 „
White oxide of tin .....: 1 „
Mix these in a biscuit-ware mortar; put them on a Dutch tile in the muffle; make it red hot, and suffer it gradually to cool. Then for use, mix with 1 part of this compound, 1$ of flux, and grind them in water.
Red lead .................. 12 parts
Red sulphate of iron ... 1 „
Oxide of antimony...... 4 „
Flint powder ............ 3 „
Calcine these without melting, and then fuse 1 part with 2J of a flux.
Sulphate of iron calcined, dark, 1 part
Red sulphate of iron...... 1 part
Flux No. 1.................. 3 „
White lead ...............1 1/2 „
Manganese..................2 1/4 parts
Red lead .................8 1/2 „
Flint powder............... 4 „
Sometimes gold leaf-—powder of gold. Gold is precipitated in aqua regia. by adding to it a watery solution, of green vitriol (proto sulphate of iron).
Gold is applied in a metallic state. For this purpose it is dissolved in aqua regia, and the acid being subsequently dissipated by heat, the gold remains as a powder at the bottom of the vessel. Silver.................. Oxide of platinum.
There are several other modes of preparing some of the colours just enumerated, but, as this small work is intended only for the use of the artist, it would be unnecessary to elaborate details which belong exclusively to the province of the manufacturer.
Metallic oxides, although the only bases of vitrifiable colours, are not alike serviceable in the decoration of Ceramic ware. The highly volatile character of the oxides of mercury, and of arsenic, are of this class; and others, so rapidly lose the oxygen, which they hold in combination, that every variation of heat, materially affects their tints. Of such are the puce and red oxides of lead, the yellow oxide of gold, green oxide of copper, and black oxide of iron.