ime. If the piece is left out in the open one gets not only the effect
of light but also that of climate on the colour, and there is no doubt
wind, rain, hail and snow have some influence on the fading of the
colour.

If the piece is exposed under glass, the climatic influences do not come
into play, and one gets the effect of light alone.

In making tests of fastness, the dyer will and does pay due regard to
the character of the influences that the material will be subjected to
in actual use, and these vary very considerably; thus the colour of
underclothing need not be fast to light, for it is rarely subjected to
that agent of destruction. On the other hand it must be fast to washing,
for that is an operation to which underclothing is subjected week by
week.

Window curtains are much exposed to light and air, and, therefore,
colours in which they are dyed should be fast to light and air. On the
other hand these curtains are rarely washed, and so the colour need not
be quite fast to washing. And so with other kinds of fabrics, there are
scarcely two kinds which are subjected to the same influences, and
require the colours to have the same degree of fastness.

The fastness to rubbing is generally tested by rubbing the dyed cloth on
a piece of white paper.

=Fastness to Washing.=--This is generally tested by boiling a swatch of
the cloth in a solution of soap containing 4 grams of a good neutral
curd soap per litre for ten minutes and noting the effect--whether the
soap solution becomes coloured and to what degree, or whether it remains
colourless, and also whether the colour of the swatch has changed at
all.

One very important point in connection with the soaping test is whether
a colour will run into a white fabric that may be soaped along with it.
This is tested by twisting strands of the dyed yarn or cloth with white
yarn or cloth and boiling them in the soap liquor for ten minutes and
then noting the effect, particularly observing whether the white pieces
have taken up any colour.

Fastness to acids and fastness to alkalies is observed while carrying
out the various acid and alkali tests given above.

CHAPTER IX.

EXPERIMENTAL DYEING AND COMPARATIVE DYE TESTING.

Every dyer ought to be able to make experiments in the mordanting and
dyeing of textile fibres for the purpose of ascertaining the best
methods of applying mordants or dye-stuffs, the best methods of
obtaining any desired shade, and fo