22 
ON CALICO-PRINTING BY DR, THOMSON. 
of pearl ashes. ^ 4. The cloth is now almost 
bleached; it requires only to be steeped in 
water holding in solution about four per cent, 
of sulphuric acid, to complete the process. 
Cotton cloth at an average, takes about two 
days to bleach. But, when there happens to 
be occasion for greater dispatch, it is no un- 
common thing to complete the bleaching and 
callendring in twentj^-four hours. 
PRINTING.— There are two modes of 
printing, namely, block-printing and cylin- 
der -printing . 1 he f'rmer has been prac- 
tised from time immemorial ; the latter is a 
modern invention, and originated, probably, 
after the introduction of the art of printing 
into Great Britain. 
The block is a piece of sycamore, (or, more 
commonly, a fir board, on which a piece of 
sycamore is glued) on which, the pattern in- 
tended to be printed on the cloth is cut. The 
parts which are to make the impression, are 
left prominent, while the rest of the block is 
cut away ; just as is practised for wood en- 
gravings. When the pattern is too compli- 
cated, and the lines too fine to be cut in wood, 
they are made by means of small rieces of 
copper, draw n out into narrow ribbons of the 
requisite fineness ; these are ingeniously 
driven into the block, and the intervals are 
filled up with felt. Great patience and in- 
genuity are displayed in making these blocks 
for use, and calico-printers are under the 
necessity of keeping a number of workmen, 
at high wages, for that express piirnose. 
The inventors and drawers of the patterns, 
constitute another class of ingenious artists, 
in the pay of the calico-printers at high wages. 
The cylinder is a large cylinder of copper, 
about a yard in length, and four or five inches 
in diameter, upon which the pattern to be 
printed on the cloth is engraved. This cy- 
linder is made to revolve, and press against 
the cloth, taking up the mordants, or colours 
to be printed on the cloth as it revolves. By 
this ingenious contrivance, two or even three 
different colours, are printed on the cloth at 
once, and the printing proceeds, w ithout in- 
terruption, till a whole piece, or indeed, any 
number of pieces attached to each other are 
printed. 
Another method of printing is almost the 
same as copper plate printing. The patterns 
is engraved upon a flat copper plate, a yard or 
more square. Uponthi-s plate, the colour or 
mordant to be applied, is spread. It is then 
pulled. As it passes along, an elastic steel 
plate, called a doctor, takes oft' all the colour, 
except that which feels the engraving. Being 
pressed against the cloth in the act of pulling, 
it prints upon it either in mordants or colour.s, 
as may be the impression of the pattern. 
Whether the printing is applied by the 
block, the cylinder, or the flat plate, the treat- 
ment of the goods is nearly the same. 
t An impure Soda ash is now very generally 
used by bleachers. For, as every hundred 
pounds of crystallized carbonate of Soda con- 
tains 62 | of water, the expense of carriage is 
more than double, and although the form in- 
dicates in some measure the purity of this salt, 
every bleacher knows how to estimate the value 
of the drier preparation. 
Most commonly, the printing process is 
employed to fix the mordants upon the cloth, 
which is afterwards dyed in the usual way. 
Those parts only retain the colour which have 
imbibed the mordant, while the other parts of 
the cloth remain white. Sometimes acids, or 
other substances, are printed on cloth already 
dyed, to remove the colour from certain por- 
tions of it which are to be left w'hite, or to re- 
ceive some other colour. 
Occa.sionally, substances are printed on 
cloth before it is dipt in the indigo vat, to pre- 
vent the blue colour from becoming fixed on 
those parts to which they are applied. Substan- 
ces possesed of these properties are called re- 
sist pastes. 
It is a very common practice to communi- 
cate mordants and colouring matters to cloth 
at the same time. 
We must give a sketch of the different sub- 
stances thus applied, before proceeding to de- 
tail the dilferent processes. 
I. MOR HANTS.— The term mordant is 
applied by dyers to certain substances with 
w hich the cloth is impregnated before it is 
dyed, otherwise the colour would not fix, but 
would disappear on washing or exposure to 
the light. The name was given by the French 
dyers (from the Latin word mordere, to 
bite,) from a notion entertained by them that 
the action of mordants wms mechanical, that 
they were of a corrosive, or biting nature, and 
served merely to open the pores of the cloth, 
into which the colouring matter might in- 
sinuate itself. It is now understood that 
their action is chemical. They have an affini- 
ty to the cloth, which causes them to adhere 
to it ; while the colouring matter has an 
affinity for, and adheres to, the mordant. 
The usual mordants employed by the calico- 
printer, ai*e the three following : — 
1. Jlumina, or the alu7n mordant. 
1 his mordant is made by dissolving alum in 
water, and adding acetate of lime to the solu- 
tion. The liquid has a specific gravity of 
J.fS, and contains about as much alum unde- 
composed, as the liquid can hold in solution. 
For particular purposes, calico-printers make 
a mordant by mixing three parts of acetate of 
lead with four of alum. This mordant con- 
sists of a mixture of acetate of alumina and 
alum ; for about a third part of the alum re- 
mains undecomposed. 
When cloth is imtiregnated with this mor- 
dant, such is the affinity of the alumina for 
the cloth, that the acetate of alumina, and even 
a portion of the alum, are decomposed, and 
the particles of alumina adhere to the fibres of 
the cloth so firmly that they cannot be remov- 
ed by w ashing. 
In order to determine the quantity of alumi- 
na fixed on the cloth by the aluming process, 
1 got a quantity of the cotton cloth that was 
to be dyed Turkey-red; 1000 grains of this 
cloth were burnt, and the ashes being reserv- 
ed, and subjected to a chemical analy.sis, were 
found to contain 0.4 grain of alumina; 1000 
grains of the same cloth after being dyed 
Turkey-red, and of course, impregnated with 
the alum mordant, were treated in the same 
way. The alumina obtained amounted to 8 
grains. The length of a piece of this cloth , 
