LAKES. Under this title are compris ed all those colors which consist of a ve getable dye, combined by precipitation with a white earthy basis, which is usu ally alumina. The general method of preparation is to add to the colored infu sion a solution of common alum, or rather a solution of alum saturated with potash, especially when the infusion has been made with the aid of acids. At first only a slight precipitate falls, consisting of alu mina and the coloring matter ; but on adding potash, acopious precipitation en sues, of the alumina associated with the dye. When the dyes are not injured, but are rather brightened by alkalies, the above process is reversed ; a decoction of the dye-stuff is made with an alkaline li quor, and when it is filtered, a solution of alum is poured into it. The third method is practicable only with substances hav ing a great affinity for subsulphate of alu mina; it consists in agitating recently precipitated alumina with the decoction of the dye.
Yellow lakes are made with a decoction of Persian or French berries, to which some potash or soda is added ; into the mixture a solution of alum is to be pour ed as long as any precipitate falls. The precipitate must be filtered, washed, and formed into cakes; and dried. A lake may be made in the same way with quer citron, taking the precaution to purify the decoction of the dye-stuff with butter milk or glue. After filtering the lake, it may be brightened with a solution of tin. Annotto lake is formed by dissolving the dye-stuff in a weak alkaline ley, and add ing alum water to the solution. Solution of tin gives thiS lake a lemon yellow cast ; acids a reddish tint.
Red lakes.—The finest of these is car mine.
This beautiful pigment was accidentally discovered by a Franciscan monk at Pisa. He formed an extract of cochineal with salt of tartar, in order to employ it as a medicine, and obtained, on the addition of an acid to it, a fine red precipitate. Homberg published a process for prepar ing it, in 1656. Carmine is the coloring matter of cochineal, prepared by pre cipitation from a decoction of the drug. Its composition varies according to the mode of making it. The ordinary car mine is prepared with alum, and consists of earmulfum (see CocringraL), a little ani mal matter, alumina, and sulphuric acid. See CARIIEVE.
Carminated lake, called lake of Florence, Paris, or Vienna. For making this pig ment, the liquor is usually employed which is decanted from the carmine pro cess. Into this, newly precipitated alu mina is put ; the mixture is stirred, and heated a little, but not too much. When ever the alumina has absorbed the color, the mixture is allowed to settle, and the liquor is drawn off.
Sometimes alum is dissolved in the de coction of cochineal, and potash is then added, to throw down the alumina in combination with the coloring matter ; but in this way an indifferent pigment is obtained. Occasionally, solution of tin is added, to brighten the dye.
A lake may be obtained from kermes, in the same way as from cochineal ; but now it is seldom had recourse to. Brazil-wood lakes. Brazil-wood is to be boiled in .a proper quantity of water for 15 minutes • then, alum and solution of tin being added, the liquor is to be fil tered, and a solution of potash poured in as long as it occasions a precipitate. This is separated by the filter, washed in pure water, mixed with a little gum water, and made into cakes. Or, the Brazil-wood may be boiled along with a little vinegar, the decoction filtered, alum and salt of tin added, and then potash-ley poured in to precipitate the lake. For 1 lb. of Bra zil wood, 80 to 40 lbs. of water, and from to 2 lbs. of alum, may be taken, in pro ducing a deep red lake ; or the same pro portions with half a pound of solution of tin. If the potash be added in excess, the tint will become violet. Cream of tartar occasions a brownish east.
Madder lake. A fine lake may be ob tained from madder, by washing it in cold water as long as it gives out color ; then sprinkling some solution of tin over it, and setting it aside for some days. A gentle heat may also be applied. The red liquor must be then separated by the fil ter, and decomposed by the addition of carbonate of soda, when a fine red preci pitate will be obtained. Or, the reddish brown coloring matter of a decoction of madder may be first separated by acetate of lead, and then the rose-red color with alum. Or, madder tied up in a bag is boiled in water ; to the decoction, alum is added, and then potash. The precipi tate should be washed with boiling water, till it ceases to tinge it yellow ; and it is then to be dried.
The following process merits a pre ference : Diffuse 2 pounds of ground madder in 4 quarts of water, and after a maceration of 10 minutes, strain and squeeze the grounds in a press. Repeat this macera tion, &c., twice upon the same portion of madder. It will now have a fine rose color. It must be mixed with 5 or 6 lbs. of water and half a lb. of bruised alum, and heated upon a warm bath for 3 or 4 hours, with the addition of water, as it evaporates, after which the whole must be thrown upon a filter cloth. The liquor which passes is to be filtered through paper, and then precipitated by carbo nate of potash. If the potash be added in three successive doses, three different lakes will be obtained, of successively di minishing beauty. The precipitates must be washed till the water conies off color less.
Blue lakes are hardly ever prepared, as indigo, Prussian blue, cobalt and ultramarine, answer every purpose of blue pigments.
Green lakes are made by a mixture of yellow lakes with blue pigments ; but chrome yellows mixed with blues produce almost all the requisite shades of green. LAMINABLE is said of a metal, which may be extended by passing between steel or hardened (chilled) cast-iron roll ers. See Icon.