Aurum Musivum, or Mosaicum, is a combination of tin and sulphur, having the appearance of bright gold in powder. It is used by japanners, and for varnished works, as snuff-boxes, tea-trays, etc, also to statue and plaster figures. The usual process of preparing it is as follows: amalgate 12 parts of the purest tin with 3 parts of mercury; the amalgam is then triturated in a stone mortar with 7 parts of the flour of sulphur, and 3 parts of muriate of ammonia. The mixture is next put into a matrass, and the whole exposed to a gentle sand heat, until no more white fumes arise. After this, the heat is somewhat raised, and cinnabar sublimes, together with some oxygenated muriate of tin, while at the same time the remaining tin and sulphur unite, forming the aurum inusivum, exhibiting a golden yellow, and flaky scaly matter of a metallic lustre. The principal point to be attended to is the regulation of the fire; for if the heat be too great, the aurum musivum fuses to a dark-coloured sulphuret of tin. The process of the Marquis de Bouillon, as described by Chaptal, differs from the foregoing in the proportions; and the experiments of the latter chemist are also worthy of notice.
The marquis's process consisted in amalgamating 8 oz. of tin with 8 oz. of mercury, and mixing with this 6 oz. of sulphur, and 4 oz. of muriate of ammonia. This mixture is to be exposed for three hours to a sand heat, sufficient to render the bottom of the matrass obscurely red hot. Chaptal, however, found that if the matrass containing the mixture were exposed to a naked fire and violently heated, the mixture took fire, and a sublimate was formed in the neck of the matrass, consisting of the most beautiful aurum musivum in large hexagonal plates. Bergman mentions a native aurum musivum from Siberia, consisting of tin, sulphur, and a small proportion of copper. According to Dr. John Davy, the aurum mosaicum, or mosaic gold, consisted of 100 tin, and 56.25 sulphur. Berzelius makes the proportions 100 tin, and 52.3 sulphur. The mean of those results, viz. 100 tin+ 54.2 sulphur, may therefore be regarded as the correct proportions. A few years ago a patent was taken out by Messrs. Parker and Hamilton, for an alloy of copper and zinc, which they termed the true mosaic gold.
The specification directs that equal quantities of copper and zinc are to be melted at the lowest temperature at which the former will fuse, when they are to be well stirred and mixed together; small quantities of zinc are then added by degrees, until the alloy assumes the desired colour. It is essential that the heat should be as low as possible, to prevent the rapid evaporation of the zinc. The alloy first assumes a yellow colour; the addition of more zinc turns it first to a purplish tint, which ultimately becomes perfectly white,"which is the colour it should have when in a state of fusion. It may then be cast into ingots for use; but it is preferable to cast the alloy, in the first instance, into the forms required, as a portion of the zinc flies off on remelting.