The majority of the colouring matters used in the preparation of lakes are of vegetable origin, but several are derived from animal sources. The properties of the colouring matters used for this purpose vary greatly; each material demands a special treatment for the production of lakes. Therefore, in describing the methods by which lakes are made, we shall give first the properties of the colouring matter in question, and then proceed to the preparation of the lake. In the preceding portion of the book the pigments have been arranged according to their colour; the lakes will be described in the same order. The yellow, red or green lakes of different origin will be treated in the same section in order to facilitate reference to any particular pigment. White lakes are not known, neither are there lakes which can be described as black. With these exceptions lakes of all colours can be made and also of all shades. As an example of this madder lake may be given, which is found in commerce in a great variety of shades; it can be made from the palest rose-red to the deepest purple red, or, more properly, madder red, which is a characteristic shade. The shades of any lake are obtained by mixing in a white pigment just as in the manufacture of mineral pigments. Whilst, however, in the latter case the white pigment must often be mechanically mixed with the colour, the shading of the lakes is accomplished in their preparation. Generally speaking, a pale shade of a lake is obtained by increasing the amount of the salt, the oxide of which is used to precipitate the colouring matter. The oxides in question are white (with the exception of lead oxide); thus in the pale shades a small amount of colouring matter is precipitated upon a large amount of oxide, whilst in the deep lakes the reverse is the case, a large quantity of colouring matter is precipitated upon a small quantity of oxide, and the shade thus appears very deep. Apart from the nature of the colouring matter contained in a lake, and considering only the metallic oxide with which the colouring matter is united, it appears that lakes containing lead oxide have little durability. The combination between the colouring matter and the metallic oxide in a lake is so loose that it is easily destroyed by sulphuretted hydrogen; if a lake containing lead is exposed to the action of air containing that gas the colour will, in the course of time, inevitably blacken. The lakes containing tin are also susceptible to sulphuretted hydrogen; in air containing but a trace of this gas they quickly lose their brilliance and in time are quite discoloured.