Nutgalls.
Lamp black.
Blue.—The coarser kind of paper used for packing is prepared from rags blued with indigo, which, when reduced to pulp, are not subjected to the process of bleaching. The finer kinds of paper are blued in various ways, but the chief material used is what is known as artificial ultramarine, of which there are many qualities in the market, to which reference is made in another chapter. Prussian blue is also used, but this is usually produced directly in the beating-engine by adding in solution, 95 parts of sulphate of iron and 100 parts of ferrocyanide of potassium (yellow prussiate of potash). Smalts blue, which was formerly much used before the introduction of artificial ultramarine, is still preferred for high-classed papers as the colour is more permanent. To obtain smalts in an exceedingly fine state of division the best plan is to grind the colour in a little water, and then to separate the finest particle by the process of elutriation, that is, by diffusing the reduced mass through a large volume of water, and after allowing the larger particles to subside, pouring off the liquor in which the finer particles are suspended, to a separate vessel, in which they are allowed to subside. If this operation is carefully conducted the smalts may be obtained in an exceedingly fine state of division, and we have found that in this state the colour blends well with the pulp, and has little or no disposition to sink through it, but produces a uniform colouring throughout.
American Combinations for Colouring.—Hofmann gives the following examples of the combination of colours which have been adopted by American manufacturers:—
Yellow Gold Envelope of fine quality is made of—
| Bichromate of potash | 10 lbs. |
| Nitrate of lead | 18 " |
| Orange mineral | 56 " |
| Porous alum | 30 " |
each substance being separately dissolved and added to 400 lbs. of pulp.
Orange-red Gold Envelope:—
| Bichromate of potash | 7 lbs. |
| Nitrate of lead | 10½ " |
| Orange mineral | 60 " |
| Porous alum | 20 " |
These substances are dissolved separately and added to 400 lbs. of pulp.