e is
but one remedy. Wash same in Fuller's earth, and if the shade is then
too pale, re-dye. If, through bad management of the vats, the yarn is
dull, pass the yarn through a hot bath (100% water, 1% acetic acid)
and wash in two waters. If yarn is streaky, take 10 gallons of water
at 120 deg.F., 1 oz. of hydrosulphite powder, 2 fluid ozs. liquid
ammonia fort. 880, and let yarn lie in same for 60 minutes. Wash in two
waters.

The following facts should be carefully noted:--

The Caustic Soda is the _alkali_ which dissolves the Indigo White.

The Hydrosulphite _reduces_ the Indigotine in the Indigo to _Indigo
White_.

Indigo White is fixed on the yarn as Indigo White and on exposure to
the air becomes blue.

The yarn, on removal from the vat, should come out greenish yellow or
a greenish blue. The latter is for blue yarn and should not turn blue
too quickly (allow 60 seconds at least).

Rest the vats for 1 hour after 3 hours work. Never hurry the vats. It
is a good thing to have hydrosulphite slightly in excess as this
prevents premature oxidization; too much will strip off the indigo
white already deposited on the yarn.

Caustic Soda must always be used with the greatest caution or the yarn
will be tendered and ruined.

Finally, unless the yarn is completely scoured it is impossible to
obtain a clear colour, or a blue which will not rub off.

The figures given are for Indigo bearing 100% Indigotine, therefore in
using vegetable Indigo do not add _all_ the Caustic or Hydrosulphite,
but depend on the glass test rather than on measurements.

_WOAD_

Woad is derived from a plant, _Isatis tinctoria_, growing in the North
of France and in England. It was the only blue dye in the West before
Indigo was introduced from India. Since then woad has been little used
except as a fermenting agent for the Indigo vat. It dyes woollen cloth
a greenish colour which changes to a deep blue in the air. It is said
to be inferior in colour to indigo but the colour is much more
permanent. The leaves when cut are reduced to a paste, kept in heaps
for about fifteen days to ferment, and then are formed into balls
which are dried in the sun; these have a rather agreeable smell and
are of a violet colour. These balls are subjected to a further
fermentation of nine weeks before being used by the dyer. When woad is
now used it is always in combination with indigo, to improve the
colour. Even by itself, however, it yields a good and ve