Of Copying With Altered Dimensions





147. Of the pentagraph. This mode of copying is chiefly used

for drawings or maps: the instrument is simple; and, although

usually employed in reducing, is capable of enlarging the size of

the copy. An automaton figure, exhibited in London a short time

since, which drew profiles of its visitors, was regulated by a

mechanism on this principle. A small aperture in the wall,

opposite the seat in which the person is placed whose profile is

taken, conceals a camera lucida, which is placed in an adjoining

apartment: and an assistant, by moving a point, connected by a

pentagraph with the hand of the automaton, over the outline of

the head, causes the figure to trace a corresponding profile.



148. By turning. The art of turning might perhaps itself be

classed amongst the arts of copying. A steel axis, called a

mandril, having a pulley attached to the middle of it, is

supported at one end either by a conical point, or by a

cylindrical collar, and at the other end by another collar,

through which it passes. The extremity which projects beyond this

last collar is formed into a screw, by which various instruments,

called chucks, can be attached to it. These chucks are intended

to hold the various materials to be submitted to the operation of

turning, and have a great variety of forms. The mandril with the

chuck is made to revolve by a strap which passes over the pulley

that is attached to it, and likewise over a larger wheel moved

either by the foot, or by its connection with steam or water

power. All work which is executed on a mandril partakes in some

measure of the irregularities in the form of that mandril; and

the perfect circularity of section which ought to exist in every

part of the work, can only be ensured by an equal accuracy in the

mandril and its collar.



149. Rose engine turning. This elegant art depends in a great

measure on copying. Circular plates of metal called rosettes,

having various indentations on the surfaces and edges, are fixed

on the mandril, which admits of a movement either end-wise or

laterally: a fixed obstacle called the 'touch', against which the

rosettes are pressed by a spring, obliges the mandril to follow

their indentations, and thus causes the cutting tool to trace out

the same pattern on the work. The distance of the cutting tool

from the centre being usually less than the radius of the

rosette, causes the copy to be much diminished.



150. Copying dies. A lathe has been long known in France, and

recently been used at the English mint for copying dies. A blunt

point is carried by a very slow spiral movement successively over

every part of the die to be copied, and is pressed by a weight

into all the cavities; while a cutting point connected with it by

the machine traverses the face of a piece of soft steel, in which

it cuts the device of the original die on the same or on a

diminished scale. The degree of excellence of the copy increases

in proportion as it is smaller than the original. The die of a

crown-piece will furnish by copy a very tolerable die for a

sixpence. But the chief use to be expected from this lathe is to

prepare all the coarser parts, and leave only the finer and more

expressive lines for the skill and genius of the artist.



151. Shoe-last making engine. An instrument not very unlike

in principle was proposed for the purpose of making shoe lasts. A

pattern last of a shoe for the right foot was placed in one part

of the apparatus, and when the machine was moved, two pieces of

wood, placed in another part which had been previously adjusted

by screws, were cut into lasts greater or less than the original,

as was desired; and although the pattern was for the right foot,

one of the lasts was for the left, an effect which was produced

by merely interposing a wheel which reversed the motion between

the two pieces of wood to be cut into lasts.



152. Engine for copying busts. Many years since, the late Mr

Watt amused himself with constructing an engine to produce copies

of busts or statues, either of the same size as the original, or

in a diminished proportion. The substances on which he operated

were various, and some of the results were shewn to his friends,

but the mechanism by which they were made has never been

described. More recently, Mr Hawkins, who, nearly at the same

time, had also contrived a similar machine, has placed it in the

hands of an artist, who has made copies in ivory from a variety

of busts. The art of multiplying in different sizes the figures

of the sculptor, aided by that of rendering their acquisition

cheap through the art of casting, promises to give additional

value to his productions, and to diffuse more widely the pleasure

arising from their possession.



153. Screw cutting. When this operation is performed in the

lathe by means of a screw upon the mandril, it is essentially an

art of copying, but it is only the number of threads in a given

length which is copied; the form of the thread, and length as

well as the diameter of the screw to be cut, are entirely

independent of those from which the copy is made. There is

another method of cutting screws in a lathe by means of one

pattern screw, which, being connected by wheels with the mandril,

guides the cutting point. In this process, unless the time of

revolution of the mandril is the same as that of the screw which

guides the cutting point, the number of threads in a given length

will be different. If the mandril move quicker than the cutting

point, the screw which is produced will be finer than the

original; if it move slower, the copy will be more coarse than

the original. The screw thus generated may be finer or coarser--

it may be larger or smaller in diameter--it may have the same or

a greater number of threads than that from which it is copied;

yet all the defects which exist in the original will be

accurately transmitted, under the modified circumstances, to

every individual generated from it.



154. Printing from copper plates with altered dimensions.

Some very singular specimens of an art of copying, not yet made

public, were brought from Paris a few years since. A watchmaker

in that city, of the name of Gonord, had contrived a method by

which he could take from the same copperplate impressions of

different sizes, either larger or smaller than the original

design. Having procured four impressions of a parrot, surrounded

by a circle, executed in this manner, I shewed them to the late

Mr Lowry, an engraver equally distinguished for his skill, and

for the many mechanical contrivances with which he enriched his

art. The relative dimensions of the several impressions were 5.5,

6.3, 8.4, 15.0, so that the largest was nearly three times the

linear size of the smallest; and Mr Lowry assured me, that he was

unable to detect any lines in one which had not corresponding

lines in the others. There appeared to be a difference in the

quantity of ink, but none in the traces of the engraving; and,

from the general appearance, it was conjectured that the largest

but one was the original impression from the copperplate.



The means by which this singular operation was executed have

not been published; but two conjectures were formed at the time

which merit notice. It was supposed that the artist was in

possession of some method of transferring the ink from the lines

of a copperplate to the surface of some fluid, and of

retransferring the impression from the fluid to paper. If this

could be accomplished, the print would, in the first instance, be

of exactly the same size as the copper from which it was derived;

but if the fluid were contained in a vessel having the form of an

inverted cone, with a small aperture at the bottom, the liquid

might be lowered or raised in the vessel by gradual abstraction

or addition through the apex of the cone; in this case, the

surface to which the printing-ink adhered would diminish or

enlarge, and in this altered state the impression might be

retransferred to paper. It must be admitted, that this

conjectural explanation is liable to very considerable

difficulties; for, although the converse operation of taking an

impression from a liquid surface has a parallel in the art of

marbling paper, the possibility of transferring the ink from the

copper to the fluid requires to be proved.



Another and more plausible explanation is founded on the

elastic nature of the compound of glue and treacle, a substance

already in use in transferring engravings to earthenware. It is

conjectured, that an impression from the copperplate is taken

upon a large sheet of this composition; that this sheet is then

stretched in both directions, and that the ink thus expanded is

transferred to paper. If the copy is required to be smaller than

the original, the elastic substance must first be stretched, and

then receive the impression from the copperplate: on removing the

tension it will contract, and thus reduce the size of the design.

It is possible that one transfer may not in all cases suffice; as

the extensibility of the composition of glue and treacle,

although considerable, is still limited. Perhaps sheets of India

rubber of uniform texture and thickness, may be found to answer

better than this composition; or possibly the ink might be

transferred from the copper plate to the surface of a bottle of

this gum, which bottle might, after being expanded by forcing air

into it, give up the enlarged impression to paper. As it would

require considerable time to produce impressions in this manner,

and there might arise some difficulty in making them all of

precisely the same size, the process might be rendered more

certain and expeditious by performing that part of the operation

which depends on the enlargement or diminution of the design only

once; and, instead of printing from the soft substance.

transferring the design from it to stone: thus a considerable

portion of the work would be reduced to an art already well

known, that of lithography. This idea receives some confirmation

from the fact, that in another set of specimens, consisting of a

map of St Petersburgh, of several sizes, a very short line,

evidently an accidental defect, occurs in all the impressions of

one particular size, but not in any of a different size.



155. Machine to produce engraving from medals. An instrument

was contrived, a long time ago, and is described in the Manuel de

Tourneur, by which copperplate engravings are produced from

medals and other objects in relief. The medal and the copper are

fixed on two sliding plates at right angles to each other, so

connected that, when the plate on which the medal is fixed is

raised vertically by a screw, the slide holding the copperplate

is advanced by an equal quantity in the horizontal direction. The

medal is fixed on the vertical slide with its face towards the

copperplate, and a little above it.



A bar, terminating at one end in a tracing point, and at the

other in a short arm, at right angles to the bar, and holding a

diamond point, is placed horizontally above the copper; so that

the tracing point shall touch the medal to which the bar is

perpendicular, and the diamond point shall touch the copperplate

to which the arm is perpendicular.



Under this arrangement, the bar being supposed to move

parallel to itself, and consequently to the copper, if the

tracing point pass over a flat part of the medal, the diamond

point will draw a straight line of equal length upon the copper;

but, if the tracing point pass over any projecting part of the

medal, the deviation from the straight line by the diamond point,

will be exactly equal to the elevation of the corresponding point

of the medal above the rest of the surface. Thus, by the transit

of this tracing point over any line upon the medal, the diamond

will draw upon the copper a section of the medal through that

line.



A screw is attached to the apparatus, so that if the medal be

raised a very small quantity by the screw, the copperplate will

be advanced by the same quantity, and thus a new line of section

may be drawn: and, by continuing this process, the series of

sectional lines on the copper produces the representation of the

medal on a plane: the outline and the form of the figure arising

from the sinuosities of the lines, and from their greater or less

proximity. The effect of this kind of engraving is very striking;

and in some specimens gives a high degree of apparent relief. It

has been practised on plate glass, and is then additionally

curious from the circumstance of the fine lines traced by the

diamond being invisible, except in certain lights.



From this description, it will have been seen that the

engraving on copper must be distorted; that is to say, that the

projection on the copper cannot be the same as that which arises

from a perpendicular projection of each point of the medal upon a

plane parallel to itself. The position of the prominent parts

will be more altered than that of the less elevated; and the

greater the relief of the medal the more distorted will be its

engraved representation. Mr John Bate, son of Mr Bate, of the

Poultry, has contrived an improved machine, for which he has

taken a patent, in which this source of distortion is remedied.

The head, in the title page of the present volume, is copied from

a medal of Roger Bacon, which forms one of a series of medals of

eminent men, struck at the Royal Mint at Munich, and is the first

of the published productions of this new art.(3*)



The inconvenience which arises from too high a relief in the

medal, or in the bust, might be remedied by some mechanical

contrivance, by which the deviation of the diamond point from the

right line (which it would describe when the tracing point

traverses a plane), would be made proportional not to the

elevation of the corresponding point above the plane of the

medal, but to its elevation above some other parallel plane

removed to a fit distance behind it. Thus busts and statues might

be reduced to any required degree of relief.



156. The machine just described naturally suggests other

views which seem to deserve some consideration, and, perhaps,

some experiment. If a medal were placed under the tracing point

of a pentagraph, an engraving tool substituted for the pencil,

and a copperplate in the place of the paper; and if, by some

mechanism, the tracing point, which slides in a vertical plane,

could, as it is carried over the different elevations of the

medal, increase or diminish the depth of the engraved line

proportionally to the actual height of the corresponding point on

the medal, then an engraving would be produced, free at least

from any distortion, although it might be liable to objections of

a different kind. If, by any similar contrivance, instead of

lines, we could make on each point of the copper a dot, varying

in size or depth with the altitude of the corresponding point of

the medal above its plane, than a new species of engraving would

be produced: and the variety of these might again be increased,

by causing the graving point to describe very small circles, of

diameters, varying with the height of the point on the medal

above a given plane; or by making the graving tool consist of

three equidistant points, whose distance increased or diminished

according to some determinate law, dependent on the elevation of

the point represented above the plane of the medal. It would,

perhaps, be difficult to imagine the effects of some of these

kinds of engraving; but they would all possess, in common, the

property of being projections, by parallel lines, of the objects

represented, and the intensity of the shade of the ink would

either vary according to some function of the distance of the

point represented from some given plane, or it would be a little

modified by the distances from the same plane of a few of the

immediately contiguous points.



157. The system of shading maps by means of lines of equal

altitude above the sea bears some analogy to this mode of

representing medals, and if applied to them would produce a

different species of engraved resemblance. The projections on the

plane of the medal, of the section of an imaginary plane, placed

at successive distances above it, with the medal itself, would

produce a likeness of the figure on the medal, in which all the

inclined parts of it would be dark in proportion to their

inclination. Other species of engraving might be conceived by

substituting, instead of the imaginary plane, an imaginary sphere

or other solid, intersecting the figure in the medal.



158. Lace made by caterpillars. A most extraordinary species

of manufacture, which is in a slight degree connected with

copying, has been contrived by an officer of engineers residing

at Munich. It consists of lace, and veils, with open patterns in

them, made entirely by caterpillars. The following is the mode of

proceeding adopted: he makes a paste of the leaves of the plant,

which is the usual food of the species of caterpillar(4*) he

employs, and spreads it thinly over a stone, or other flat

substance. He then, with a camel-hair pencil dipped in olive oil,

draws upon the coating of paste the pattern he wishes the insects

to leave open. This stone is then placed in an inclined position,

and a number of the caterpillars are placed at the bottom. A

peculiar species is chosen, which spins a strong web; and the

animals commencing at the bottom, eat and spin their way up to

the top, carefully avoiding every part touched by the oil, but

devouring all the rest of the paste. The extreme lightness of

these veils, combined with some strength, is truly surprising.

One of them, measuring twenty-six and a half inches by seventeen

inches, weighed only 1.51 grains; a degree of lightness which

will appear more strongly by contrast with other fabrics. One

square yard of the substance of which these veils are made weighs

4 1/3 grains, whilst one square yard of silk gauze weighs 137

grains, and one square yard of the finest patent net weighs 262

1/2 grains. The ladies' coloured muslin dresses, mentioned in the

table subjoined, cost ten shillings per dress, and each weigh six

ounces; the cotton from which they are made weighing nearly six

and two-ninth ounces avoirdupois weight.



Weight of one square yard of each of the following articles(5*)



Weight of

Weight cotton used

Value finished of in waking

per yard one square one square

Description of goods measure yard yard



s. d. Troy grains Troy grains



Caterpillar veils -- 4 1/3 --

Silk gauze 3-4 wide 1 0 137 --

Finest patent net -- 262 1/2 --

Fine cambric muslin -- 551 --

6-4ths jaconet muslin 2 0 613 670

Ladies' coloured muslin dresses 3 0 788 875

6-4ths cambric 1 2 972 1069

9-8ths calico 0 9 988 1085

1/2-yard nankeen 0 8 2240 2432





159. This enumeration, which is far from complete, of the

arts in which copying is the foundation, may be terminated with

an example which has long been under the eye of the reader;

although few, perhaps, are aware of the number of repeated

copyings of which these very pages are the subject.



1. They are copies, by printing, from stereotype plates.



2. These stereotype plates are copied, by the art of casting,

from moulds formed of plaster of Paris.



3. These moulds are themselves copied by casting the plaster

in a liquid state upon the moveable types set up by the

compositor.



[It is here that the union of the intellectual and the

mechanical departments takes place. The mysteries, however, of an

author's copying, form no part of our enquiry, although it may be

fairly remarked, that, in numerous instances, the mental far

eclipses the mechanical copyist.]



4. These moveable types, the obedient messengers of the most

opposite thoughts, the most conflicting theories, are themselves

copies by casting from moulds of copper called matrices.



5. The lower part of those matrices, bearing the impressions

of the letters or characters, are copies, by punching, from steel

punches on which the same characters exist in relief.



6. These steel punches are not themselves entirely exempted

from the great principle of art. Many of the cavities which exist

in them, such as those in the middle of the punches for the

letters a, b, d, e, g, etc., are produced from other steel

punches in which these parts are in relief.



We have thus traced through six successive stages of copying

the mechanical art of printing from stereotype plates: the

principle of copying contributing in this, as in every other

department of manufacture, to the uniformity and the cheapness of

the work produced.



NOTES:



1. The late Mr Lowry.



2. I posses a lithographic reprint of a page of a table, which

appears, from the from of the type, to have been several years

old.



3. The construction of the engraving becomes evident on examining

it with a lens of sufficient power to show the continuity of the

lines.



4. The Phalaena pardilla, which feeds on the Prunus padus.



5. Some of these weights and measures are calculated from a

statement in the Report of the Committee of the House of Commons

on Printed Cotton Goods; and the widths of the pieces there given

are presumed to be the real widths, not those by which they are

called in the retail shops.





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