Buff Envelope of fine deep shade is made from—
| Bichromate of potash | 3 lbs. |
| Nitrate of lead | 5 " |
| Orange mineral | 10 " |
| American ochre | 20 " |
| Porous alum | 30 " |
Some half-stuff of red jute bagging. For 400 lbs. of pulp.
Tea-Colour is made from a decoction of quercitron bark, the liquid being poured into the engine, and 2 lbs. of copperas in solution are added for every gallon of the bark extract. A little ultramarine may be used to brighten the colour.
Drab.—Venetian red, well washed, added to a pulp of tea-colour made as above will give a fine drab.
Brown is composed of several colours, or a very fine dark green tea-colour brown, containing tea, buff, drab, and ink-grey, may be made of—
| Quercitron bark liquid | 15 | gals. |
| Bicarbonate of soda | 2 | lbs. |
| Venetian red | 4 | " |
| Extract of nutgalls | 2½ | " |
| Copperas | 18 | " |
| Porous alum | 30 | " |
The above proportions are for 400 lbs. of pulp.
The large proportion of alum prescribed in all the above examples serves as a mordant, and also, with the addition of resin soap, for sizing. All the above mixtures should be passed through a No. 60 wire-cloth into the beating-engine.
Mixing Colouring Materials with Pulp.—It will be readily understood that when paper is sized in the pulp, as Mr. Hofmann points out, the resinous alumina surrounds the fibres and prevents the colouring materials from penetrating them. In such cases the colouring materials are only loosely held, and a portion must therefore be lost in the machine. If added to the pulp before it is sized they become thoroughly mixed with the fibres, and with them enveloped by the size. The pulp should always be coloured before it is sized, except in cases where the alum or resin soap would injure the colours, or be injured by them. While the pulp is being sized and coloured, the finishing touch is given by the engine-man, who examines it and empties it into the stuff-chest.