t a colored compound insoluble in
water, and hence "safe." For example, cotton material dyed directly in
logwood solution has almost no value, but if it is soaked in a
solution of oxalic acid and alum until it becomes saturated with the
chemicals, and is then transferred to a logwood bath, the color
acquired is fast and beautiful.

This method of indirect dyeing is known as the mordanting process; it
consists of saturating the fabric to be dyed with chemicals which will
unite with the coloring matter to form compounds unaffected by water.
The chemicals are called mordants.

229. How Variety of Color is Secured. The color which is fixed on
the fabric as a result of chemical action between mordant and dye is
frequently very different from that of the dye itself. Logwood dye
when used alone produces a reddish brown color of no value either for
beauty or permanence; but if the fabric to be dyed is first mordanted
with a solution of alum and oxalic acid and is then immersed in a
logwood bath, it acquires a beautiful blue color.

Moreover, since the color acquired depends upon the mordant as well as
upon the dye, it is often possible to obtain a wide range of colors by
varying the mordant used, the dye remaining the same. For example,
with alum and oxalic acid as a mordant and logwood as a dye, blue is
obtained; but with a mordant of ferric sulphate and a dye of logwood,
blacks and grays result. Fabrics immersed directly in alizarin acquire
a reddish yellow tint; when, however, they are mordanted with certain
aluminium compounds they acquire a brilliant Turkey red, when
mordanted with chromium compounds, a maroon, and when mordanted with
iron compounds, the various shades of purple, lilac, and violet
result.

230. Color Designs in Cloth. It is thought that the earliest
attempts at making "fancy materials" consisted in painting designs on
a fabric by means of a brush. In more recent times the design was cut
in relief on hard wood, the relief being then daubed with coloring
matter and applied by hand to successive portions of the cloth. The
most modern method of design-making is that of machine or roller
printing. In this, the relief blocks are replaced by engraved copper
rolls which rotate continuously and in the course of their rotation
automatically receive coloring matter on the engraved portion. The
cloth is to be printed is then drawn uniformly over the rotating roll,
receiving color from the engraved design; in this