Many makers adopt an immediate washing, grinding, drying, and sifting, before the ultramarine has become entirely blue. The colour is then more uniform, because there are no green specks inside or out. The blue calcined pigment is ready for the market when it has been washed, dried, and sifted. The intensity of the blue colour depends on that of the green, but grinding generally diminishes it. Light blues are sometimes produced in the course of manufacture, and these mixed with dark ones form the medium quality. But generally the light colours are produced by addition of white pigments.
In the French method of calcination, "inuflies " are used, i.e. furnaces into which the flame of the fireplace does not penetrate. The green ultramarine is evenly spread upon the bed, in layers 1 1/2 in. thick. The door is closed, and the fire is urged until the sulphur projected into the muffle becomes inflamed. A shovelful of sulphur is charged in, and stirred with an iron hook, the door being raised just enough to allow of the motion of the hook. After the combustion of this sulphur, and an examination of a sample, a new quantity of sulphur is charged in, stirred, and so on, until the consecutive samples show no improvement in purity and intensity of colour. No greater heat is required than that necessary to ignite the sulphur as soon as put in. The transformation is more rapid with this mode than with the cylinders, because there is greater access of air, therefore more sulphurous acid produced, and less volatilization of sulphur. As soon as the ultramarine has acquired the desired colour, it is raked into a sheet-iron box under the door.
The furnace is charged again, and the operation progresses as before.
Ultramarine increases in weight by combination with sulphur, and the increase, after washing the product, may amount to several hundredths, if the washings have not been thorough, the ultramarine will form compact masses in the packing barrels. (Gentele.)
For laundry purposes, ultramarine is generally put up in balls. It is thoroughly mixed with small quantities of an adhesive substance, such as gum-arabic, dextrine, or starch, worked into a thick dough, rolled flat, cut into square blocks, and rolled by hand into balls. This work is generally done by children. Ultramarine is a better bluing agent than either soluble blue or aniline. Prussian (soluble) blue particularly will impart to clothes a yellowish rusty tint after continued use. In using ultramarine for this purpose, it should be strained through a fine cloth, and not allowed to settle, lest It should spot.
Furstenau states that by employing the following mixtures,blue ultramarine may be made in one operation) instead of the green product which is ordinarily formed by the first calcination, and which requires a second calcination to give the blue tint: -
100 to 110 parts.
90 „ 95 „
110 „ 120 „
10 „ 15 „
. 10 „
The materials are finely powdered, thoroughly mixed in the mill, and heated in round luted pots to a low red heat for 13 to 20 hours. (Dingl. Pol. Jl.)
Guimet has a process for making ultramarine of various colours. By the substitution of selenium for the sulphur in blue ultramarine, he obtains a brown and purple; if tellurium be substituted, he gets green and yellow.
This water-colour is prepared from wood-soot as follows: - The brightest and darkest soot, from the combustion of beech-wood, are powdered and passed through a silken sieve. The powder is stirred in hot water for 24 hours, and again in another water. The liquors are collected and settled. The precipitate is mixed with gum-water, and evaporated in a stove-room to the consistency of a solid extract.
Luke Nuttrass, of Nelson, New Zealand, has received a diploma of merit from the late International Exhibition at Vienna, for a new indigenous vegetable pigment prepared from the hinau tree (Elaocarpus hinau). Competent judges pronounce the pigment to be as good as if not better than sepia. It is manufactured at 6d. per oz., whereas the same weight of sepia costs lis.
Mix 2 parts caustic soda and 1 of potash chlorate; gradually add 2 very finely-powdered manganese; heat gradually up to dull redness, allow to cool, powder, and exhaust with water; filter, cool, and add a solution of baryta nitrate to the filtrate. A violet-coloured baryta precipitate forms; this is carefully washed, dried, and treated with 1/2 to 1 part caustic baryta, hydrated, and gradually heated up to redness, with constant stirring. The cooled mass is powdered, and finally washed to remove excess of baryta.
(a) Pour 3 parts saturated solution sal-ammoniac over 2 of copper-filings, contained in a vessel capable of being closed, and keep the mixture in a warm place for some weeks, when the newly-formed pigment is separated from the inoxidized copper by washing on a sieve; it is then washed with water, and slowly dried in the shade. (6) A solution of crude carbonate of ammonia is added to a mixed solution of alum and blue vitriol as long as it affects it; in a short time, the precipitate is collected, washed, and dried, (c) Lighter shades are produced by the addition of baryta sulphate or alum.
Barium chromate is precipitated by adding to a solution of barium chloride a sufficiency of a soluble chromate to effect complete separation; to the lemon-yellow chromate is added 20 per cent, of strong sulphuric acid, which produces a deep red by the liberation of chromic acid; the mass is then ground, and heated to redness, when it becomes green.