60. Massicot,
Or Masticot, is a protoxide of lead, varying from the purest and most tender straw colour to a dull orange yellow, and known as Light, Yellow, and Golden Massicot. It has in painting all the properties of white lead, from which it may be prepared by gentle calcination in an open furnace. In tint with that pigment, however, it soon loses its colour and returns to white, probably extracting some carbonic acid therefrom. If used in an unmixed state, it is permanent in oil under the same conditions as white lead, but should not be employed in water, on account of its changing even to blackness by the action of damp or impure air. It is an admirable dryer, and has much the same effect as litharge in rendering oils siccative.
Litharge is merely fused massicot. Old writers speak of litharge of silver and litharge of gold, oxides of lead, pale and reddish yellow respectively. Commercial litharge, especially that which is foreign, contains sometimes a considerable proportion of oxide of copper and iron. The principal impurity, however, is generally silica, left undissolved on treating the litharge with nitric or acetic acid. Litharge is commonly used in preparing drying oils, which contain a greater or less amount of the oxide in the form of oleate of lead. Oils made siccative by means of litharge are therefore liable to be damaged by foul gas. It is a matter of congratulation that such injury is not lasting, and that the oil, like white lead, recovers its original colour on exposure to air and light. Some drying oil which we exposed on a tile to an atmosphere of sulphuretted hydrogen until it was completely blackened, regained its former yellow hue on being submitted for a day or so to air and light. Hence, although the employment of lead as a siccative is not desirable, its effects are not so deleterious as might be imagined.
61. Patent Yellow,
Turner's Yellow, Montpellier Yellow, Mineral Yellow, Cassel Yellow, &c., is a mixture of chloride and oxide of lead, obtainable either as a pale or a deep yellow. It is a hard, ponderous, sparkling substance, of a crystalline texture and bright colour; hardly inferior, when ground, to chrome yellow. Of an excellent body, and working well in oil and water, but soon injured both by the sun's light and impure air. A variety, mentioned by Mérimée, in which bismuth and antimony are also used, is of greater durability.
62. Platinum Yellow.
Our own opinion of this costly preparation is that the good qualities of the product do not justify its price. It may be obtained as a bright, rich, deep yellow, of considerable transparency; but the colour is acted upon by foul gas and exposure. Even in a book we have found it assume a dirty greyish cast, and a specimen which had been kept in a drawer, wrapped up in paper, became perfectly black in a few years. The presence of palladium interferes with the beauty of the original tint, but does not affect its stability.
63. Thallium Yellow.
The new metal thallium yields in combination with chromic acid two yellow colours, a pale and an orange. They are not absolutely insoluble in water, and the sulphide of thallium being brown, would probably be damaged by impure air. But whatever their properties as pigments may be, their habitudes as such are not yet known. The present scarcity of the metal renders the colours produced from it mere scientific curiosities.