cause of loose shades. The remedy is
obvious, _viz_., the discarding of such vats and the preparation of
new ones, in fact old vats are perhaps more fruitful sources of loose
shades than any other cause. Soft water suits indigo dyeing better
than hard water, and is to be preferred.

It is not advisable to attempt to get full or deep shades of indigo at
one dip, for such would necessitate the use of strong baths. Dyeings
produced in this way are liable to rub badly, because the indigo lies
mostly on the surface, to which it is more or less mechanically
attached. Light shades of indigo are fast to rubbing, and by repeated
dippings in a light vat or a medium shade vat deep shades of fair
fastness to rubbing can be got.

As repeatedly stated, no indigo vat can be worked continuously with
good results; the continual agitation induced by the passage of the
yarns or cloths into the liquor brings the liquor into contact with
the air, and oxidation sets in, resulting in the indigo being thrown
out of the liquor in its original form. When this happens the vat
loses its original clear yellow or yellowish-brown colour and becomes
greenish, a sure sign that the vat is getting out of condition to give
good results. The remedy has been pointed out in dealing with each
kind of vat, and consists essentially in adding to the vat more of the
active reducing agent and allowing the vat to rest a while.

The dye-vats may be either round tubs or square wooden tanks; for yarn
in hanks, when cloths or warps are being dyed, these may be fitted (p. 149)
with winces and guide rollers so as to draw materials through the liquor.

The hawking machine shown in figure 22 is also very good for indigo
cloth dyeing, and is largely used for this purpose.

[Illustration: Fig. 23.--Indigo Dye-vat.]

Figure 23 also shows an excellent machine for indigo dyeing on cloth.
In this the vat has a frame carrying guide rollers, round which the
cloth passes, so that it travels several times through the vat liquor
in its passage from one end of the vat to the other, the amount of
liquor in the vat being so arranged that the cloth is entirely
immersed the whole time. After going through the liquor the cloth
passes between a pair of squeezing rollers, in order to have any
surplus liquor taken out, then it traverses the space between sets of
guide rollers arranged over the vat, during which time the indigo
becomes oxidised and the blue develops, while finally it is