Of Printing From Cavities





83. The art of printing, in all its numerous departments, is

essentially an art of copying. Under its two great divisions,

printing from hollow lines, as in copperplate, and printing from

surface, as in block printing, are comprised numerous arts.



84. Copperplate printing. In this instance, the copies are

made by transferring to paper, by means of pressure, a thick ink,

from the hollows and lines cut in the copper. An artist will

sometimes exhaust the labour of one or two years upon engraving a

plate, which will not, in some cases furnish above five hundred

copies in a state of perfection.



85. Engravings on steel. This art is like that of engraving

on copper, except that the number of copies is far less limited.

A bank-note engraved as a copperplate, will not give above three

thousand impressions without a sensible deterioration. Two

impressions of a bank-note engraved on steel were examined by one

of our most eminent artists,(1*) who found it difficult to

pronounce with any confidence, which was the earliest impression.

One of these was a proof from amongst the first thousand, the

other was taken after between seventy and eighty thousand had

been printed off.



86. Music printing. Music is usually printed from pewter

plates, on which the characters have been impressed by steel

punches. The metal being much softer than copper, is liable to

scratches, which detain a small portion of the ink. This is the

reason of the dirty appearance of printed music. A new process

has recently been invented by Mr Cowper, by which this

inconvenience will be avoided. The improved method, which give

sharpness to the characters, is still an art of copying; but it

is effected by surface printing, nearly in the same manner as

calico-printing from blocks, to be described hereafter, 96. The

method of printing music from pewter plates, although by far the

most frequently made use of, is not the only one employed, for

music is occasionally printed from stone. Sometimes also it is

printed with moveable type; and occasionally the musical

characters are printed on the paper, and the lines printed

afterwards. Specimens of both these latter modes of

music-printing may be seen in the splendid collection of

impressions from the types of the press of Bodoni at Parma: but

notwithstanding the great care bestowed on the execution of that

work, the perpetual interruption of continuity in the lines,

arising from the use of moveable types, when the characters and

lines are printed at the same time, is apparent.



87. Calico printing from cylinders. Many of the patterns on

printed calicos are copies by printing from copper cylinders

about four or five inches in diameter, on which the desired

pattern has been previously engraved. One portion of the

cylinders is exposed to the ink, whilst an elastic scraper of

very thin steel, by being pressed forcibly against another part,

removes all superfluous ink from the surface previously to its

reaching the cloth. A piece of calico twenty-eight yards in

length rolls through this press, and is printed in four or five

minutes.



88. Printing from perforated sheets of metal, or stencilling.

Very thin brass is sometimes perforated in the form of letters,

usually those of a name; this is placed on any substance which it

is required to mark, and a brush dipped in some paint is passed

over the brass. Those parts which are cut away admit the paint.

and thus a copy of the name appears on the substance below. This

method, which affords rather a coarse copy, is sometimes used for

paper with which rooms are covered, and more especially for the

borders. If a portion be required to match an old pattern, this

is, perhaps the most economical way of producing it.



89. Coloured impressions of leaves upon paper may be made by

a kind of surface printing. Such leaves are chosen as have

considerable inequalities: the elevated parts of these are

covered, by means of an inking ball, with a mixture of some

pigment ground up in linseed oil; the leaf is then placed between

two sheets of paper, and being gently pressed, the impression

from the elevated parts on each side appear on the corresponding

sheets of paper.



90. The beautiful red cotton handkerchiefs dyed at Glasgow

have their pattern given to them by a process similar to

stencilling, except that instead of printing from a pattern, the

reverse operation that of discharging a part of the colour from a

cloth already dyed--is performed. A number of handkerchiefs are

pressed with very great force between two plates of metal, which

are similarly perforated with round or lozenge-shaped holes,

according to the intended pattern. The upper plate of metal is

surrounded by a rim, and a fluid which has the property of

discharging the red dye is poured upon that plate. This liquid

passes through the holes in the metal, and also through the

calico; but, owing to the great pressure opposite all the parts

of the plates not cut away, it does not spread itself beyond the

pattern. After this, the handkerchiefs are washed, and the

pattern of each is a copy of the perforations in the metal-plate

used in the process.



Another mode by which a pattern is formed by discharging

colour from a previously dyed cloth, is to print on it a pattern

with paste; then, passing it into the dying-vat, it comes out

dyed of one uniform colour But the paste has protected the fibres

of the cotton from the action of the dye or mordant; and when the

cloth so dyed is well washed, the paste is dissolved, and leaves

uncoloured all those parts of the cloth to which it was applied.





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