DYEING. 
672 
cloth, which is then dipped into the solution 
containing the dye-stuff. The dye-stuff com* 
nines with the intermediate substance, which, 
being firmly combined with the doth, se- 
cures the permanence of the dye. Sub- 
stances employed for this purpose are de- 
aominated mordants. 
1 he most important part of dyeing, is un- 
doubtedly the proper choice, and the proper 
application, of mordants ; as upon them, the 
permanency of almost every dye depends. 
Every thing which has been said respecting 
the application of colouring matters, applies 
equally to the application of mordants. They 
must be previously dissolved in some liquid, 
winch has a weaker ‘affinity for them than the 
cloth has, to which they are to be applied; 
and the cloth must be dipped, or even steep- 
ed in this solution, in order to saturate itself 
with the mordant. 
Almost the only substances used as mor- 
dants, are earths, metallic oxides, tan, and 
oil. 
Of earth)' mordants the most important, 
and most generally used, is alumina. It is 
used either in the state ot common alum, in 
which it is combined with sulphuric acid, or 
in that of acetite of alumina. 
Ajpm, when used as a mordant, is dissolved 
in water, and very frequently a quantity, of 
tartar is dissolved along with it. Into this 
solution the doth js put, and kept in it till it 
has absorbed as much alumina as is neces- 
sary. Jt is then taken out, and for the most 
part washed and dried. It is now a good deal 
heavier than it was before, owing to the alu- 
mina which has combined with it. The tar- 
tar serves two purposes ; the potass which it 
contains, combines with the sulphuric acid of 
the alum, and thus prevents that very cor- 
rosive substance from injuring the texture of 
the cloth, which otherwise might happen : 
the tartareous acid, on the other hand, com- 
bines with part ot the alumina, and forms a 
tai trite of alumina, which is more easily de- 
«om posed by the cloth than alum. 
Acetite of alumina has been but lately in- 
troduced into dyeing. This mordant is now 
prepared by pouring acetite of lead into a 
solution of alum; a double decomposition 
takes place, the sulphureous acid combines 
with the lead, and the compound precipi- 
tates, in the form of an insoluble powder, 
while the alumina combines with the acetous 
acid, and remains dissolved in the liquid. 
This mordant is employed for cotton and 
linen, which have a weaker affinity than wool 
for alumina. It answers much better than 
alum ; the cloth is mere easily saturated 
with alumina, and takes, in consequence, 
both a richer and a more permanent colour. 
Besides alumina, lime is sometimes used 
as a mordant. Cloth has. a strong affinity 
enough for it; but, in general, it does not 
answer so well, as it does not give so good a 
colour. When used, it is either in the state 
of lime-water, or of sulphate of lime dis- 
solved in water. 
Almost all the metallic oxides have an af- 
finity for cloth, but only two of them are ex- 
tensively used as mordants, namely, the ox- 
ides of tin, and of iron. 
The oxide of tin was first introduced into 
dyeing by Kuster, a German chemist, who 
•brought the secret to London in 1543. This 
period forms an sera' in the history of dyeing. 
The oxide of tin has enabled the moderns 
9 
greatly to surpass the antients in the fineness 
of their colours; by means of it alone, scar- 
let, the brightest ot all colours, is produced. 
Tin, as Proust lias proved, is capable of 
two degrees of oxydation. The first oxide 
is composed of 0.70 parts of tin, and 0.30 of 
oxygen; the second, of white oxide, of 0.60 
parts of tin, and 0.40 of oxy gen. The first 
oxide absorbs oxygen with" very great fa- 
cility, even from the air, and is rapidly con- 
verted into white oxide. 'Phis fact makes it 
certain, that it is the white oxide of tin alone, 
which is the real mordant; even if the other 
oxide was applied to cloth, as it probably 
often is, it must soon be converted into white 
oxide, by absorbing oxygen from the atmo- 
sphere. 
Tin is used as a mordant in three states : 
dissolved in nitro-muriatic add, in acetous 
acid, and in a mixture of sulphuric and muri- 
atic acids. NitTO-muriate- of tin is the com- 
mon mordant employed by dyers. They 
prepare it by dissolving tin in diluted nitric 
acid, to which a certain proportion of muri- 
ate of soda (common salt), or of ammonia 
(sal ammoniac), is added. Part of the nitric 
acid decomposes these salts, combines with 
their base, and sets the muriatic acid at li- 
berty. It was prepared at first with nitric 
acid alone, but that mode was very defective, 
because the nitric acid very readily converts 
tin to white oxide, and then is incapable of 
dissolving it ; the consequence of which 
was, the precipitation of the whole of the tin. 
To remedy this defect, common salt, or sal 
ammoniac, was very soon added ; muriatic 
acid having the property of dissolving white 
oxide of tin very readily. A considerable 
saving of nitric acid might be obtained, by 
employing as much sulphuric acid as is just 
sufficient to saturate the base of the common 
salt, or sal ammoniac, employed. 
When the nitro-muriate of tin is to be used 
as a mordant, it is dissolved in a large quan- 
tity of water, and the cloth is dipped in the 
solution, and allowed to remain till sufficient- 
ly saturated. It is then taken out, and wash- 
ed and dried. Tartar is usually dissolved in 
the water along with the nitro-muriate. The 
consequence- of this is a double decompo- 
sition : the nitro-muriatic acid combines with 
the potass of the tartar, while the tartareous 
acid dissolves the oxide of tin. When tartar 
is used, therefore, in any considerable quan- 
tity, the mordant is not a nitro-muriate, but 
a tartrite of tin. 
Iron, like tin, is capable of two degrees of 
oxydation; but the green oxide absorbs oxy- 
gen so readily from the atmosphere, that. ‘it 
is very soon converted into the red oxide. 
It is only this last oxide which is really used 
as a mordant in dyeing. The green" oxide 
is, indeed, sometimes applied to cloth ; but 
it very soon absorbs oxygen, and is converted 
into the red oxide. This oxide lias a very 
strong affinity for all kinds of cloth. The 
permanency of the iron-spots on linen and 
cotton is a sufficient proof of this. As a 
mordant, it is used in two states ; in that of 
sulphate^ of iron (copperas), and acetite of 
iron. 'Plie first is commonly used for wool. 
The salt is dissolved in water, and the cloth 
dipped in it. It may be used also for cot- 
ton, but in most cases acetite of iron is pre- 
ferred. It is prepared by dissolving iron, or 
its oxide, in vinegar, sour beer, &c. and the 
longer it is kept, the *nore it is preferred. 
The reason is, that this mordant succeeds 
best when the iron is in the state of red 
oxide. It would be better then to oxidate 
the iron, or convert it into rust, before using 
it ;_ which might ’be easily done, by keeping 
it for some time in a moist place, and sprink- 
ling it occasionally with water 
J an lias a very strong affinity for cloth, 
and for several colouring matters’; it is there- 
fore very frequently employed as a mordant. 
An infusion of nut-galls, or of sumach, or any 
other substance containing tan, is made in 
water, and the cloth is dipped in this in- 
fusion, and allowed to remain till it has ab- 
sorbed a sufficient quantity of tau. Silk b 
capable of absorbing a very great proportion 
of tan, and by that means acquires a great 
increase of weight. Manufacturers some- 
times -employ this method of increasing the 
weight of silk. 
Tan is often employed also, along with 
other mordants, in order to produce a com- 
pound mordant. Oil is also used for the 
same purpose, in the dyeing of cotton and 
linen. The mordants with which tan most 
frequently is combined, are alumina, and 
oxide of iron. 
Besides these mordants, '..there are several, 
other substances frequently used as auxili- 
arms, either to facilitate the combination of 
the mordant with the cloth, or to alter the 
shade of colour; the chief of these are, tar- 
tar, acetite of lead, common salt, sal am- 
moniac, sulphate or acetite of copper, Sec. 
Mordants not only render the dye perma- 
nent, but have also considerable * influence 
on the colour produced. The same colour- 
ing matter produces very different dyes, ac- 
cording as the mordant is changed. Sup- 
pose, for instance, that the colouring matter 
is cochineal ; if we use the aluminous mor- 
dant, the cloth will acquire a crimson co- 
lour ; but the oxide of iron produces with it 
a black. 
In dyeing then, it is not only necessary to 
procure a mordant which I as a sufficiently 
strong affinity for the colouring matter and 
the cloth, and a colouring matter which pos- 
sesses the wished-for colour in perfection, 
but we must procure a mordant and a co- 
louring matter of such a nature, that when 
combined together, they shall possess the 
wished-for colour in perfection. It is evident 
too, that a great variety of colours may be 
produced with a single dye-stuff, provided 
we can change the mordant sufficiently. 
T he colouring matter with which the cloth 
is dyed, does not cover every portion of its 
surface; its particles attach themselves to the 
cloth at certain distances from each other; 
for cloth may be dyed different shades of 
the same colour, lighter or darker, merely 
by varying the quantity of colouring matter. 
With a small quantity, the shade “is light; 
and it becomes deeper as the quantity in- 
creases. Now this would be impossible, * 
if the dye-stuff covered the whole of t he cloth. 
I hat the particles of colouring matter, 
even when the shade is deep, are at some 
distance, is evident from tins well-known 
fact, that cloth may be dyed two colours at 
the same time. All those colours to which 
the dyers give the name of compound, are 
in fact two different colours applied to the 
cloth at once. Thus cloth gets a green co- 
lour, by being first dved blue and then Yel- 
low. 
