CHROME
(Potassium dichromate. Bichromate of Potash.)
Chrome is a modern mordant, unknown to the dyer of fifty years ago. It is excellent for wool and is easy to use and very effective in its action. Its great advantage is that it leaves the wool soft to the touch, whereas the other mordants are apt to harden the wool. The wool should be boiled for 1 to 1-1/2 hours with bichromate of potash in the proportion of 2 to 4 per cent of the wool. It is then washed well and immediately dyed. Wool mordanted with chrome should not be exposed to light, but should be kept well covered with the liquid while being mordanted, else it is liable to dye unevenly. An excess of chrome impairs the colour, 3 per cent of chrome is a safe quantity to use for ordinary dyeing. It should be dissolved in the bath while the water is heating. The wool is entered and the bath gradually raised to the boiling point, and boiled for 3/4 of an hour.
COPPER
(Copper Sulphate, Verdigris, Blue Vitriol, Blue Copperas, Bluestone.)
Copper is rarely used as a mordant. It is usually applied as a saddening agent, that is, the wool is dyed first, and the mordant applied afterwards to fix the colour. With cream of tartar it is used sometimes as an ordinary mordant before dyeing, but the colours so produced have no advantage over colours mordanted by easier methods.