Various examples of mordanting with alum.—
For silk. Wet out the silk thoroughly with water and wring out. Then work it about a little in a strong solution of alum, previously dissolved in hot water, and steep for several hours (or over night). Then wash well. It should not be allowed to dry before dyeing. "Silks are always alumed in the cold, because when they are alumed in a hot bath, they are apt to lose a portion of their lustre." Berthollet.
For wool. ¼ lb. of Alum and 1 oz. Cream of tartar for every pound of wool. This is dissolved and when the water is warm the wool is entered. Raise to boiling point and boil for one hour. The bath is then taken off the fire and allowed to cool over night. The wool is then wrung out (not washed) and put away in a linen bag in cool place for four or five days, when it is ready for dyeing.
For cotton and linen. After boiling in water (some use a sour water, some an alkaline ley) the cotton is put into the alum bath, ¼ lb. of Alum to 1 lb. of cotton. The alum is dissolved in hot water with soda in the proportion of 1 part soda to 16 of alum. (Some add a small quantity of tartar and arsenic). The cotton is well worked in this solution and left 24 hours. It is then washed, and afterwards galled.
For linen. ¼ lb. alum for every pound of linen. Boil for 2½ hours and immediately put into the dye bath.
For wool. 6 to 8 per cent. of alum and 5 to 7 per cent. of tartar of the weight of wool.
IRON. (Ferrous Sulphate, copperas, green vitriol)
Iron is one of the oldest mordants known and is largely used in wool and cotton dyeing. It is almost as important as alum. With wool it should be used in combination with cream of tartar. The temperature of the mordanting bath must be raised very gradually to boiling point or the wool will dye unevenly. A general method of dealing with copperas is to boil the wool first in a decoction of the colouring matter and then add the mordant to the same bath in a proportion of 5 to 8 per cent. of the weight of wool: and continue boiling for half an hour or so longer. With some dyes a separate bath is needed, such as with Camwood or Catechu. If used for cotton, the cotton is first dyed in a boiling decoction of the dye stuff and then passed through a cold solution of ferrous sulphate. Probably the commonest way of applying copperas in cotton dyeing is to prepare the cotton with tannin, pass through clear lime water and then through a copperas solution. Great care is needed in the using of copperas, as, unless it is thoroughly dissolved and mixed with the water before the wool is entered, it is apt to stain the wool. It also hardens wool if used in excess, or if boiled too long.
Copperas is mostly used for the fixing of wool colours (Fustic etc.) to produce brown shades by the "stuffing and saddening" method (see [page 14]), the wool being boiled first in a decoction of the dye for about an hour, and then for ½ an hour with the addition of 5 to 8 per cent. of copperas. If used for darkening colours, copperas is added to the bath, after the dyeing, and the boiling continued for 15 to 20 minutes.
Examples of various proportions for Mordanting.—