THOMSON ON CALICO PRINTING. 
103 
ON CALICO-PRINTING. 
By Thomas Thomson, M. D,, F. R. S. 
L. and E. &c. &c. 
Regius Professor of Chemistry in the Uni- 
versity of Qlasgotv. 
{Continued from page 64.) 
III.— RLSIST PASTES.— These are sub- 
stances which have the property of restoring 
tlie blue colour of dissolved indigo, and thus, 
of preventing it from becoming fixed on those 
parts to which the resist-pastes have been ap- 
plied. Any substance which the property of 
readily parting with oxygen, answ'ers this pur- 
pose. ISulphate of copper, or any salt contain- 
ing black oxide of copper, when put into the 
indigo vat, instantly revives the indigo, by 
communicating oxygen to it. The hydrated 
black oxide of copper has the same effect, 
and so have the sesquioxide and deutoxide of 
manganese. 
The calico-printer’s indigo vat is a very 
deep large vessel filled with water, into which 
indigo, sulphate of iron, and an excess of lime 
are put. The lime decomposes the sulphate 
of iron, and the disengaged protoxide of iron 
coming in contact with the indigo at the bot- 
tom of the vat, deprives it of an atom of oxy- 
gen, and thus renders it capable of combining 
with the lime, and of forming a compound 
which dissolves in water, and forms a yellow 
liquid. Where this solution is in contact 
with the atmosphere, the indigo is revived, 
assumes its blue colour, and loses its solubi- 
lity. Hence, the blue scum which always 
covers the surface. But this scum, in some 
measure, protects the rest of the vat. When 
cloth is dipt into this vat it comes out yellow. 
But from the exposure, the indigo gradually 
absorbs oxygen and becomes blue. The cloth 
at first, from the mixture of the blue and yel- 
low, has a green colour, which slowly deepens 
into blue. But if, to any parts of the cloth 
before it be dipped into the vat, something 
has been applied w'hich has the property of 
giving out oxygen to the indigo ; all the indigo 
which would be imbibed by these parts is 
revived, before it comes in actual contact 
with cloth ; and, in the revived state, it is in- 
capable of combining chemically with the 
cloth, but may be easily washed off. Hence, 
the parts covered by resist-pastes remain 
white, 
' The following are the principal resist- 
pastes used by calico-printers : 
1, BLUE PASTE OR VITRIOL con- 
sistofa mixture of sulphate and acetate of 
copper, and the solution is thickened with 
gum-senegal and pipe-clay for the block, and 
with flour, for the cylinder. When the cloth 
on which this paste has been printed is dipt 
into the indigo vat, the indigo is revived be- 
fore it has time to reach the surface of the 
cloth. After dyeing, the piece is passed 
through weak sulphuric acid, to remove the 
oxide of copper which has been precipitated 
on it. 
2, MILD PASTE consists of sulphate 
of zinc, gum, and pipC'Clay, It is used along 
with colours which copper would injure, or 
which would be destroyed by immersion in 
sulphuric acid. It resists a pale blue and the 
removal of the oxide of zinc by an acid, is not 
necessary, as it is when copper has been em- 
ployed. 
Sulphate of zinc, as well as all the other 
metallic salts and all the acids, precipitates 
indigo from its solution in lime. It does not 
revive the indigo like the salts of copper; but 
when the base of indigo is precipitated, it is 
not so readily fixed as a state solution. The 
oxide of zinc with the gum and pipe-clay, 
acts mechanically in keeping it at a distance. 
3. RED PASTE consists of the alum 
mordant already described, mixed with acetate 
of copper, gum, and pipe-clay. It resists 
pale blues, and the alumina remains upon the 
white portions of the cloth, to be afterwards 
dyed red, with madder or yellow by quer- 
citron bark. 
4. NEUTPvAL PASTE is a name given 
by printers, to a compound of lime juice, 
sulphate of copper, gum, and pipe-clay. It 
resists during a short dip in the blue vat ; 
and the lime juice gives it the property of 
remaining white when the piece is dyed 
in madder, even when the preceding red 
paste goes over it. Tliis acid also prevents 
the lime of the blue vat from precipitating 
copper upon the cloth, which would cause 
the parts to assume a deep brown tinge when 
dipt into the madder vessel. 
5. CHROME YELLOW RESIST 
PASTE consists of a mixture of a salt of cop- 
per, to resist the blue vat with a salt of lead, 
to produce a yellow with bichromate of po- 
tash, after having been dyed in the blue vat. 
The preceding observations were necessary, 
to give the reader an idea of the various pro- 
cesses, followed by the calico-printers, and 
with the rationale of them. I shall now pro- 
ceed to explain the different colours. And 
both the simplest and most intelligible method 
of proceeding seems to be, to place pieces of 
printed calico before the eyes of the reader, 
and describe the way in which the colours on 
them have been produced. We shall begin 
with the simplest colours, and proceed gra- 
dually to more complex ones, 
1. MADDER RED.— The alum more 
mordant described above, is made into a paste, 
and printed on the cloth by the cylinder. Af- 
ter being dried and exposed in a warm room, 
till the alumina has had time to leave the 
acid with which it was united, and combine 
w'ith cloth, it is passed through a hot mixture 
of cow’s dung and water. It is then washed 
in cold water, and agitated a second time in 
the same hot mixtuie. After being thus 
freed from all soluble or loose matter, it is 
dyed in madder. This process consists in the 
exposure of the cloth to the action of madder, 
suspended in water. In consequence of the 
very sparing solubility of the colouring mat- 
ter of that root, and the difficulty of applying 
it equally to all parts of the cloth, the pro- 
cess requires to be conducted slowly, and the 
heat to be very gradually raised. The purest 
portion of the colouring matter being first 
given out by the madder, the degree of heat 
