BLUE
INDIGO, WOAD, LOGWOOD
_INDIGO_
Indigo is the blue matter extracted from a plant _Indigofera
tinctoria_ and other species, growing in Asia, South America and
Egypt. It reaches the market in a fine powder, which is insoluble in
water. There are two ways of dyeing with Indigo. It may be dissolved
in sulphuric acid or oil of vitriol, thereby making an indigo extract.
This process was discovered in 1740. It gives good blue colours but is
not very permanent, darker colours are more so than the paler. It does
not dye cotton or linen.
The other method is by the Indigo vat process which produces fast
colours but is complicated and difficult. In order to colour with
indigo it has to be deprived of its oxygen. The deoxidized indigo is
yellow and in this state penetrates the woollen fibre; the more
perfectly the indigo in a vat is deoxidized, the brighter and faster
will be the colour. For wool dyeing the vats are heated to a
temperature of 50 deg.C. Cotton and linen are generally dyed cold.
TO MAKE EXTRACT OF INDIGO
1 lb. oil of vitriol (pure, not commercial).
2 oz. finely ground Indigo.
1/2 oz. precipitated chalk.
Mix a little of the indigo with a small quantity of oil of vitriol,
add a little chalk and stir well. Go on mixing gradually till all is
used up. This should take an hour or two. Stir a few times each day
for 4 or 5 days, adding about 1/2 oz. more of chalk by degrees. It is
best mixed in a glass stoppered bottle or jar, and stirred with a
glass rod. It must be kept from the air.
INDIGO EXTRACT (4 to 6 lbs. wool).
Mordant[E] 25% Alum. Stir 2 to 3 ozs. Indigo extract into the water of
dye bath. The amount is determined by the depth of shade required.
When warm, enter the wool and bring slowly to boiling point (about 1/2
an hour) and continue boiling for another 1/2 hour. By keeping it
below boiling point while dyeing, better colours are got, but it is
apt to be uneven. Boiling levels the colour but makes the shade
greener. This is corrected by adding to the dye bath a little logwood,
10 to 20 per cent which should be boiled up separately, strained, and
put in bath before the wool is entered; too much logwood dims the
colour. Instead of logwood a little madder is sometimes used; also
Cudbear or Barwood.
INDIGO VAT (TIN) FOR WOOL
To 2 quarts of water add 1/4 lb. lime, and make hot. Then add 1 oz.
indigo pounded up with a little of the lime water; let it stand and
get warmer. Pound up 1/2 oz. tin, _Stannous Chloride_, in a little
lime water and add, together with 1/2 oz. zinc. Add more lime water or
tin according to the state of the vat. There should be a streaky scum
on the surface, and the water underneath clear with a green tinge.
Pearl ash can be used instead of lime.
HYDROSULPHITE-SODA VAT FOR WOOL
2 ozs. powdered indigo.
7 fluid ozs. Caustic Soda solution (SG 1.2).
4 pints Sodium Hydrosulphite (SG 1.1).
_The Stock Solution._--Take 2 ozs. of well pounded indigo, with enough
warm water (120 deg.F.) to make a paste, and _grind_ in a pestle and
mortar for 10 minutes. Empty into a saucepan, capacity 1 gallon. Take
12 fluid ozs. of water adding gradually 3 ozs. of commercial caustic
soda 76 per cent. This will give a solution of SG 1.2, which can be
tested with a hydrometer reading from 1000 to 2000, the 1000
representing SG 1 as for water.
Next take 5 pints water, add hydrosulphite slowly, stirring gently
until a reading of 1100 is shown (SG 1.1) on the hydrometer. If the
hydrosulphite be weighed beforehand and the stock of the same be kept
free from damp air, or great heat, for future vats the hydrometer can
be dispensed with; it is simply weighed out and added slowly to the
water. If added too quickly the hydrosulphite will cake, fall to the
bottom and be difficult to dissolve.
To the saucepan containing the indigo (100 per cent) add 7 fluid ozs.
of the caustic soda solution, then gradually add 3-1/2 pints of
hydrosulphite solution, stirring gently for 15 to 20 minutes. Heat
the saucepan to 120 deg.F. and on no account to more than 140
deg.F.--_overheating will ruin the Stock Solution_--let it stand for
half an hour, then test with a strip of glass. This should show a
perfectly clear golden yellow colour (turning blue in 45 secs.
approx.), free from spots. If dark spots show, this indicates
undissolved indigo, therefore gradually add hydrosulphite solution
(2-3 fluid ozs.). Wait 15 mins. and test with glass strip; if
incorrect continue this every 15 minutes until the glass indicates
clear yellow. If the Stock Solution is greenish white and turbid,
undissolved _indigo white_ is present. Add then not more than a
teaspoonful at a time caustic soda solution until the Stock Solution
answers the glass test.
The _Dye Vat_ should contain about 10 gallons of water heated to hand
hot, 120 deg. and not above 140 deg.F. Add 3 ozs. of hydrosulphite
solution stirring carefully, let it stand for 20 minutes; this renders
harmless any undissolved oxygen. Add a small cupful of the Stock
Solution, stir carefully without splashing. The vats should be greenish
yellow and _should not feel slimy_, an indication of too much caustic.
The vat is now ready to dye and is kept at 120 deg. to 140 deg.F.
Between dips add Stock Solution as required, if the vat goes blue and
turbid add 3 to 4 fluid ozs. of hydrosulphite and warm up to 140 deg.F.
and wait 30 minutes. As a last resort add caustic soda solution very
gradually. This should not be required if the Stock Solution is
properly prepared.
Start to dye with weak vats, 20 to 40 minute dips, and finish with
stronger vats. The more dips given to obtain a fixed shade, the faster
will be the yarn to washing and rubbing. The yarn must be oxidized by
exposure to the air for the same length of time as dipped. After the
final dip, pass the yarn through a 10 gallon bath of water to which is
added 3 ozs. of sulphuric acid, pure or hydrochloric. This neutralizes
the caustic used. Wash yarn at least twice in water.
_Improvement of Defective Indigo Vat Dyes._
If, after washing until clear, the yarn should rub off badly, there 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 very permanent
blue.
It is not now known how the ancients prepared the blue dye, but it has
been stated (Dr. Plowright) that woad leaves when covered with boiling
water, weighted down for half-an-hour, the water then poured off
treated with caustic potash and subsequently with hydrochloric acid,
yield a good indigo blue. If the time of infusion be increased, greens
and browns are obtained. It is supposed that woad was "vitrum" the dye
with which Caesar said almost all the Britons stained their bodies. It
is said to grow near Tewkesbury, also Banbury. It was cultivated till
quite lately in Lincolnshire. There were four farms in 1896; one at
Parson Drove, near Wisbech, two farms at Holbeach, and one near
Boston. Indigo has quite superseded it in commerce.
LOGWOOD
(_Bois de Campeche, Campeachy Wood_)
Logwood is a dye wood from Central America, used for producing blues
and purples on wool, black on cotton and wool, and black and violet on
silk. It is called by old dyers one of the Lesser Dyes, because the
colour was said to lose all its brightness when exposed to the air.
But with proper mordants and with careful dyeing this dye can produce
fast and good colours. Queen Elizabeth's government issued an
enactment entirely forbidding the use of logwood. The person so
offending was liable to imprisonment and the pillory. The principal
use for logwood is in making blacks. The logwood chips should be put
in a bag and boiled for 20 minutes to 1/2 an hour, just before using.
RECIPES for DYEING with LOGWOOD
(1). BLACK
Mordant the wool for 1 to 1-1/2 hours with 3 per cent Chrome and 1 per
cent Sulphuric Acid. Wash and dye in separate bath for 1 to 1-1/2
hours with 50 per cent Logwood. This gives a blue black.
A dead black is got by adding 5 per cent Fustic to the dye bath.
A green black by adding more fustic. Also by adding 3 to 4 per cent
Alum to the mordanting bath a still greener shade can be obtained.
A violet black is produced by adding 2 per cent Stannous Chloride to
the dye bath and continue boiling for 20 minutes.
(2). LAVENDER
Mordant with 3 per cent Bichromate of Potash for 45 minutes and wash.
Dye with 2 per cent madder, 1 per cent logwood. Enter the wool, raise
to the boil and boil for 45 minutes. The proportion of logwood to
madder can be so adjusted as to give various shades of claret to
purple.
(3). A FAST LOGWOOD BLUE
(Highland recipe.) Mordant with 3 per cent Bichromate of Potash and
boil wool in it for 1-1/2 hours. Wash and dry wool. Make a bath of 15
to 20 per cent logwood with about 3 per cent chalk added to it. Boil
the wool for 1 hour, wash and dry. The wool can be greened by steeping
it all night in a hot solution of heather till the desired tint is
obtained.
(4). RAVEN GREY FOR WOOL
Mordant with 25 per cent Alum for 1/2 hour at boiling heat; then take
it out, add to the same liquor 5 per cent copperas, and work it at
boiling heat for 1/2 hour. Then wash. In another copper, boil 50 per
cent logwood chips for 20 minutes. Put the wool into this for 1/2
hour; then return it into the alum and copperas for 10 to 15 minutes.
Wash well.
(5). DARK RED PURPLE WITH LOGWOOD
(2-1/2 lbs.) Mordant with 25 per cent alum and 1 per cent cream of
tartar for 1 hour. Let cool in the mordant, then wring out and put
away for 4 to 5 days.
Dye with 60 per cent logwood and 25 per cent madder. Boil up the
logwood and madder in a separate bath and pour through a sieve into
the dye bath. Enter the wool when warm and bring to the boil. Boil
from 1/2 hour to 1-1/2 hours. Wash thoroughly in soft water.
(6) PURPLE
(For 1 lb.) Mordant wool with 1/4 lb. alum and 1/2 oz. tartar for one
hour; wring out and put away in a bag for some days. Dye with 1/4 lb.
logwood for 1 hour.
FOOTNOTES:
[Footnote E: If the Extract is used alone, a mordant is not
essential.]