Encyclopaedia Britannica > Volume 8, DIA-England

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r jn und clients; because in the latter case the sulphuric acid has
Col rs. a considerable action on the colouring matter, and thus
diminishes the intensity of the yellow. As the particles
of indigo have a stronger affinity for the stuff than the
yellow colouring matter, in dyeing a succession of shades
in a bath in which both are mixed, the bath being first
exhausted of the indigo, the last shades incline more to
the yellow, on account of the predominance of the yellow
colouring matter.
Lil. &c.
Sect. II.— Of the Mixture of Red and Blue, or
Purple, fyc.
By the mixture of red and blue, violet, purple, dove-
colour, lilac, and a great variety of other shades, accord¬
ing to the proportion of the substances employed, or the
predominance of the blue or the red, are produced. In
stuffs which are to be dyed violet, a deeper blue must be
given ; for purple colours, the ground requires to be of a
lighter blue ; but in lilac and other light colours, it is neces¬
sary that both the blue and the red have a light shade.
I.— Of dyeing Wool Violet, Purple, &;c.
In the attempts which have been made to communicate
a violet or purple colour to a scarlet ground, according to
the observations of Hellot, the colour is very unequal. It
becomes therefore necessary to give the blue colour first;
and for violets or purples, the shade of blue ought not to be
deeper than that of sky blue. The stuff being dyed blue,
is boiled with alum, and two fifths of tartar, and is after¬
wards dipped in a bath composed of nearly two thirds
the quantity of cochineal required for scarlet, with the
addition of tartar. The same process, indeed, as for dyre-
ing scarlet, is followed. It is a common practice to dyp
these colours after the reddening for scarlet, making such
additions of cochineal and tartar as the intensity of the
shade may require.
For lighter shades, as lilacs, dove-colours, &c. the stuff
may be dipped in the bath which has served for violet
and purple, and is now somewhat exhausted, taking care
to add a quantity of alum and tartar. For reddish shades,
such as a peach-blossom, a small proportion of solution
of tin is added. It may be observed in general, that
although the proportion of cochineal is less in dyeing
lighter shades, the quantity of tartar must not be dimi¬
nished.
To obtain the same colours, a shorter and less expen-
m lortersive process is recommended by Poerner. In this process
^ he employs sulphate of indigo. He boils the stuff in a so¬
lution of alum, in the proportion of three ounces of the
latter to one pound of the former, for an hour and a half,
and afterwards allows it to remain in the liquid for a night
after it has cooled. The dyeing bath is prepared with an
ounce and a half of cochineal, and two ounces of tartar,
which are boiled for three quarters of an hour: two ounces
and a half of sulphate of indigo are then added, the whole
is stirred, and boiled gently for fifteen minutes. The dye¬
ing operation is conducted in the usual way', and a beau¬
tiful violet is thus obtained. To have all the variety of
shades which are produced by the mixture of red and
blue, the proportion of the sulphate of indigo is increased
or diminished. It is sometimes increased to five ounces,
and diminished to five drachms, for each pound of stuff.
The quantity of cochineal is also varied, but when it is
less than an ounce the colour is dull. Different proportions
of tartar are also employed. To produce variety of shades,
the stuff is also prepared with different proportions of so¬
lution of tin.
To communicate a purple colour to wool, as well as
some other shades, logwood, with the addition of galls,
Cto ier
P1fe
f'rc loti'.
has been employed. The stuff is previously dyed blue, Compound
and, to give a brown shade, sulphate of iron is used; but Colours,
the colours thus obtained are not permanent. By the fol-
lowing process, described by Decroizille, a durable dye is
produced by means of this wood. He dissolved tin in
sulphuric acid, to which were added common salt, red aci¬
dulous tartrite of potash, and sulphate of copper; or it
may be more conveniently done by making a solution of
tin in a mixture of sulphuric acid, common salt, and wa¬
ter, to which are to be added the tartrite and sulphate
in the state of powder. Of this mordant not less than
1500 quarts were made in twenty-four hours, in a leaden
vessel to which a moderate heat was applied. A very lu¬
crative trade was carried on for three years by Decroizille,
who sold it at the rate of Is. 3d. sterling per pound.
If wool in the fleece is to be dyed, it will require a third Process,
of its weight of this mordant, while a fifth is a proportion
sufficient for stuffs. A bath is prepared of such a degree
of temperature as the hand can bear, with which the mor¬
dant is properly mixed, and the wool or stuff dipped in it
and stirred; the same degree of temperature being kept
up for two hours, and increased a little towards the end ;
after which it is taken out, aired, and well washed. A
fresh bath of pure water is prepared at the same tempe¬
rature, to which is added a sufficient quantity of the de¬
coction of logwood; the stuff is then immersed, stirred,
and the heat increased to the boiling temperature, which
is to be continued for fifteen minutes, after which, the
stuff being taken out, aired, and carefully rinsed, the pro¬
cess of dyeing is completed. If for every three pounds ot
wool one pound of decoction of logwood has been used,
and a proportionate quantity for stuffs which require less,
a fine violet colour is produced, to which a sufficient quan¬
tity of Brazil wood imparts the shade known in France by
the name of prune de Monsieur.
Logwood and Brazil, fustic and yellow wood, are co- Different
louring substances which may be fixed with advantage shades
upon wool by means of this mordant. The colour cam-from other
municated by the two first of these is liable to be changed811 8 ances‘
in the fulling by the action of the soap or urine employed
for that purpose; but this change, which is always pro¬
duced by alkaline substances, is remedied by a slightly
acid bath a little hot, called brightening, for which the
sulphuric acid has the preference. 'I he colour becomes
as deep, and frequently much brighter than before the
change. Wools which have been dyed by means of this
mordant are said to admit of being spun into a finer and
more beautiful thread than by the use of alum. Ir the
use of sulphate of copper is omitted, more beautiful co¬
lours are produced by fustic and yellow wood, as well as
by weld. An orange-red colour is communicated by mad¬
der, but not so deep as with a similar quantity of alum.
When sulphate of copper is omitted, the wool is said to
become much harsher, and the mordant thus prepared
yields but indifferent colours with logwood, and in parti¬
cular with Brazil wood. The use and carriage of this mor¬
dant are inconvenient, on account of the heavy sediment
by which the vessel is half filled under a corrosive liquor,
capable only of being kept in stone ware. T hese incon¬
veniences may be remedied by the omission of the water
in the receipt, which leaves only a paste more conve¬
niently used, and the carriage of it two fifths cheaper.
The above process is thus explained by Berthollet. The Nature of
decomposition of the muriate of soda is effected by the the process,
action of the sulphuric acid; and the muriatic acid being
thus disengaged, dissolves the tin, part of which is preci¬
pitated by means of the tartaric acid, producing the sedi¬
ment already mentioned. The oxide of copper produces
the blue with the colouring particles of the logwood; the
violet is formed by the oxide of tin with the same wood.