On the Economy of Machinery and Manufactures by Charles Babbage (english books to improve english TXT) 📕

Of Copying

82. The two last-mentioned sources of excellence in the work

produced by machinery depend on a principle which pervades a very

large portion of all manufactures, and is one upon which the

cheapness of the articles produced seems greatly to depend. The

principle alluded to is that of copying, taken in its most

extensive sense. Almost unlimited pains are, in some instances,

bestowed on the original, from which a series of copies is to be

produced; and the larger the number of these copies, the more

care and pains can the manufacturer afford to lavish upon the

original. It may thus happen, that the instrument or tool

actually producing the work, shall cost five or even ten thousand

times the price of each individual specimen of its power.

As the system of copying is of so much importance, and of

such extensive use in the arts, it will be convenient to classify

a considerable number of those processes in which it is employed.

The following enumeration however is not offered as a complete

list; and the explanations are restricted to the shortest

possible detail which is consistent with a due regard to making

the subject intelligible.

Operations of copying are effected under the following

circumstances:

by printing from cavities by stamping

by printing from surface by punching

by casting with elongation

by moulding with altered dimensions

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 banknote engraved as a copperplate, will not give above three

thousand impressions without a sensible deterioration. Two

impressions of a banknote 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

calicoprinting 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.

Printing from surface

91. This second department of printing is of more frequent

application in the arts than that which has just been considered.

92. Printing from wooden blocks. A block of box wood is, in

this instance, the substance out of which the pattern is formed:

the design being sketched upon it, the workman cuts away with

sharp tools every part except the lines to be represented in the

impression. This is exactly the reverse of the process of

engraving on copper, in which every line to be represented is cut

away. The ink, instead of filling the cavities cut in the wood,

is spread upon the surface which remains, and is thence

transferred to the paper.

93. Printing from moveable types. This is the most important

in its influence of all the arts of copying. It possesses a

singular peculiarity, in the immense subdivision of the parts

that form the pattern. After that pattern has furnished thousands

of copies, the same individual elements may be arranged again and

again in other forms, and thus supply multitudes of originals,

from each of which thousands of their copied impressions may

flow. It also possesses this advantage, that woodcuts may be used

along with the letterpress, and impressions taken from both at

the same operation.

94. Printing from stereotype. This mode of producing copies

is very similar to the preceding. There are two modes by which

stereotype plates are produced. In that most generally adopted a

mould is taken in plaster from the moveable types, and in this

the stereotype plate is cast. Another method has been employed in

France: instead of composing the work in moveable type, it was

set up in moveable copper matrices; each matrix being in fact a

piece of copper of the same size as the type, and having the

impression of the letter sunk into its surface instead of

projecting in relief. A stereotype plate may, it is evident, be

obtained at once from this arrangement of matrices. The objection

to the plan is the great expense of keeping so large a collection

of matrices.

As the original composition does not readily admit of change,

stereotype plates can only be applied with advantage to cases

where an extraordinary number of copies are demanded, or where

the work consists of figures, and it is of great importance to

ensure accuracy. Trifling alterations may, however, be made in it

from time to time; and thus mathematical tables may, by the

gradual extirpation of error, at last become perfect. This mode

of producing copies possesses, in common with that by moveable

types, the advantage of admitting the use of woodcuts: the copy

of the woodcut in the stereotype plate being equally perfect.

with that of the moveable type. This union is of considerable

importance, and cannot be accomplished with engravings on copper.

95. Lettering books. The gilt letters on the backs of books

are formed by placing a piece of gold leaf upon the leather, and

pressing upon it brass letters previously heated: these cause the

gold immediately under them to adhere to the leather, whilst the

rest of the metal is easily brushed away. When a great number of

copies of the same volume are to be lettered, it is found to be

cheaper to have a brass pattern cut with the whole of the proper

title: this is placed in a press, and being kept hot, the covers,

each having a small bit of leaf-gold placed in the proper

position, are successively brought under the brass, and stamped.

The lettering at the back of the volume in the reader’s hand was

executed in this manner.

96. Calico printing from blocks. This is a mode of copying,

by surface printing, from the ends of small pieces of copper

wire, of various forms, fixed into a block of wood. They are all

of one uniform height, about the eighth part of an inch above the

surface of the wood, and are arranged by the maker