th tin, scarlet; and with chrome or
copper, purple. Logwood, also, if mordanted with alum, gives a mauve
colour; if mordanted with chrome, it gives a blue. Fustic, weld, and
most of the yellow dyes, give a greeny yellow with alum, but an old
gold colour with chrome; and fawns of various shades with other
mordants.

Silk and wool require very much the same preparation except that in
the case of silk, high temperatures should be avoided. Wool is
generally boiled in a weak solution of whatever mordant is used. With
silk, as a rule, it is better to use a cold solution, or a solution at
a temperature below boiling point. Cotton and linen are more difficult
to dye than wool or silk. Their fibre is not so porous and will not
hold the dye stuff without a more complicated preparation. The usual
method of preparing linen or cotton is to boil it first with some
astringent. The use of astringents in dyeing depends upon the tannic
acid they contain. In combination with ordinary mordants, tannic acid
aids the attraction of the colouring matter to the fibre and adds
brilliancy to the colours. The astringents mostly used are tannic
acid, gall nuts, sumach and myrobalams. Cotton has a natural
attraction for tannic acid, so that when once steeped in its solution
it is not easily removed by washing.

ALUM

This is the most generally used of all the mordants, and has been
known as such from early times in many parts of the world. For most
colours a certain proportion of cream of tartar should be added to the
alum bath as it helps to brighten the ultimate colour. The usual
amount of alum is a quarter of a pound to a pound of wool. As a rule,
less mordant is needed for light colours than for dark. Excess of alum
is apt to make the wool sticky. The usual length of time for boiling
is about an hour. Some dyers give as much as 2-1/2 hours.

_Example of mordanting with alum_--1/4 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 a cool place for 4 or 5 days, when it is ready for dyeing,
after being thoroughly washed.

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