When bronze powder is slowly heated in a shallow vessel the colour begins to darken at a temperature not much above the boiling point of water. In consequence of the fineness of the particles of the metallic powder the copper readily takes up oxygen, and is superficially converted into copper oxide. This oxide is of a darker colour, and thus by this method the shade of the bronze can be deepened as desired. This simple operation requires a certain amount of practice to produce a product of a determined shade. The desired result is most safely attained when the bronze is spread out quite uniformly in a thin layer upon a metal plate, which is gently heated from below. The powder soon begins to darken; by cooling the plate the progress of the oxidation may be arrested at any moment. Recently bronze powders have come into the market showing all possible colours in the deepest shades, by the aid of which very remarkable colour effects can be produced. These bronzes are made by dissolving an aniline dye in a little alcohol, pouring this solution over the powder, and mixing the dye uniformly through the whole of the bronze by working the mass for a sufficient length of time. In this way bronze powders are produced which possess a green, red, blue or violet lustre, according to the colour of the dye used. These colours with metallic lustre can also be produced by bronzing the article with a white (zinc) bronze, and then coating it with a varnish in which the required aniline dye is dissolved. A bronze with a fine golden red glitter is produced by applying a golden yellow bronze and then a varnish in which a little aniline red is dissolved. It should be observed here that these effects, produced by a coat of varnish in which an aniline dye is dissolved, only turn out well when the dye is used in very small quantity, for these colours are the strongest with which we are acquainted, and in colouring power far surpass cochineal carmine, which is renowned for this property. When bronze is coloured by dyes the most varied shades can be obtained with a metallic lustre. According to Conradty a very fine blue bronze is obtained by boiling white bronze for some hours with a weak alum solution, washing and drying, and then mixing in a mortar with a strong solution of aniline blue in alcohol until the solvent has evaporated. This operation is repeated until the desired depth of shade is obtained. The bronze is then washed with pure water. Conradty also recommends that the coloured bronze should be ground with a little petroleum, and then exposed to the air to allow the petroleum to evaporate. This operation, for which no chemical reason can be given, is quite unnecessary. If other dyes or mixtures of them are used in place of aniline blue, bronzes of corresponding colour are obtained.