These are given by salts of iron, with galls, sumach, and logwood. The best black cloths are previously dyed blue with indigo.

By the mixture of various dyes, every variety of shade is produced: and often several tints from one colouring matter by the use of different mordants.

(The beautiful new dyes of the Aniline series, Mauve, Magenta, Artificial Alizarine, Aniline Blue, Violet Imperial, Aurine, etc, are obtained from coal-tar by various patented processes.)

Mordants are earthy and metallic compounds, the bases of which unites both with the fibres of the material to be dyed and the colouring matter, thus rendering the dyes fixed. In calico printing, the mordants are formed into a a paste with some gum or other thickening material, and printed with wooden blocks on the cloth; which, after being dried, etc, is passed through the liquid dyes. The colouring matter combines with the parts so printed, but is easily discharged from the other parts.

The principal Mordants are the following: - Alum Mordants. 1. Alum with one fourth its weight of tartar.

2. Acetate of Alumina. (See further back.) This is commmonly prepared in solution for the purpose; 100 parts of alum in solution, with 150 parts of pyrolignite of lime of 20° B. density, is sometimes employed.

3. A solution of alum, with crytallized carbonate of soda, in the proportion of 1 oz. to each pound of alum.

4. Hausmann's. This consists of a solution of alum with sufficient strong solution of caustic potash to re-dissolve the precipitated alumina; to which mixture a portion of linseed oil is added.

5. To 50 gallons of boiling water add 100 lbs. of alum; dissolve, and add slowly 10 lbs. of crystrallized carbonate of soda. When the effervescence is over, add 75 lbs. of sugar of lead.