IMPROVEMENTS IN PROCESSES FOR CHEMICAL AND PHYSICAL ENGRAVING BY MEANS OF PHOTOGRAPHY, IN THE MANUFACTURE OF PLATES FOR USE IN SUCH PROCESSES, AND IN APPARATUS EMPLOYED IN CONNECTION THEREWITH
Year: 1881

page_text: PROVISIONAL SPECIFICATION left by Alexander Melville Clark at the Office
of the Commissioners of Patents on the 26th August 1881.
ALEXANDER MELVILLE CLARK, of 53, Chancery Lane, in the County of
Middlesex, Patent Agent. "IMPROVEMENTS IN PROCESSES FOR CHEMICAL AND
PHYSICAL ENGRAVING BY MEANS OF PHOTOGRAPHY, IN THE MANUFACTURE OF
PLATES FOR USE IN SUCH PROCESSES, AND IN APPARATUS EMPLOYED IN
CONNECTION THEREWITH."
This Invention relates to improved processes of engraving metal plates for
printing and other purposes, and to the methods and apparatus for producing the
said plates. These processes I term respectively "physical engraving" and "photo-
chemical engraving."
I will first describe the process of photo-engraving, which I designate galvano-
engraving or "physical engraving."
In order to produce an engraved plate to any scale in half tint from nature or
from a drawing, painting, crayon, or pen and ink drawing, &c., I proceed in the
following manner-I either prepare beforehand a number of copper plates, as
hereafter described, the surfaces of which must be as polished and plane as plate
glass, and upon one of these plates I apply a bichromated gelatine print produced
from a negative of the subject to be engraved having the proper sharpness, vigour,
and intensity. Or upon the photographic negative itself, after coating it with gum
varnish containing one per cent. of bichromate of potash, I pour a certain quantity
of bichromated gelatine and allow it to dry, which negative after being exposed at
back and placed in tepid water furnishes a gelatine print in relief as before. The
dry print is kept for several hours in a damp place, that is, in a closed box at the
bottom of which is placed some moistened paper separated from the prints by a
row of glass tubes. The print is then black-leaded and applied upon an alloy in
a melted state contained in a vessel constructed as hereinafter described, which
alloy upon being submitted to slight pressure produces on cooling a metallic plate
or mould in intaglio suitable for printing from.
The fusible alloy which I preferably employ is composed of bismuth, tin, lead,
and mercury in varying proportions according to the desired hardness of the
D

page_text: mould. The vessel for containing the melted metal is arranged in the following
manner:-
Referring to the accompanying Drawings, Figure 5 represents a frame made in
two parts fastened together at A, B, by key bolts, one of said joints being
provided with a locking cam P, whereby the two parts of the frame may be
readily opened and closed. The bottom of the frame is formed of a flat iron plate
of sufficient strength. Into this vessel the fluid metal is poured, and the gelatine
print is immediately applied thereon and covered with another thick metal plate
and pressure applied for an instant. When cool the locking cam is released and
the frame raised so as to separate the two iron plates, between which are enclosed
the gelatine print and the perfect metallic mould produced therefrom, from which
the print may be readily detached.
The mould in intaglio thus produced in fusible metal is now ready for printing
from and will serve for obtaining transfer prints, 1st, for lithographic printing;
2nd, for obtaining metallic counterparts from which to obtain either printing
blocks by the ordinary means or intaglio plates by the aid of the photo-chemical
processes hereafter described. By placing this fusible metal mould in a galvanic
bath of copper, a counterpart in relief is obtained capable of reproducing galvanically
an indefinite number of intaglio metal plates which may be silvered or gilt and
worn as personal ornaments, or may be used by engravers.
The exposed prints in bichromated gelatine are of two kinds. If the photo-
graphic negative employed is a reproduction of lines, it requires no special
treatment, but if it be.a photograph from nature or an artistic drawing in half
tint, it is first covered with a thin pellicle to give the necessary grain which is
transmitted by exposure to the gelatine print, and consequently to the plate for
printing.
The grain is produced in the following manner:- -A glass plate of suitable
dimensions is coated uniformly with any kind of gummy liquid and placed in the
bottom of a box containing the opaque powder which is to form the grain, and
thoroughly shaken. I expose in the usual way beneath this plate a sheet of
colored and bichromated gelatine, and apply it upon the photographic negative
protected by the bichromated gum varnish and develop in luke warm water,
whereby the protected gelatine is dissolved as usual, leaving the insoluble parts
which form the grain desired. It will be evident that instead of producing a
uniform grain, as described, it will be easy to produce for the purposes of a photo-
graphic negative, either artistically, an-original-of-any-kind-or-mechanically,-by-
employing wire or other cloths combined in various ways in order to produce the
.effect indispensable in certain kinds of engravings.
The following relates to the application of the Invention for the reproduction of
lines by engraving either, in intaglio or relief, forming what I term a photo-
chemical engraving process.. This may be carried out in various ways:-(1). I
may in 3 hours obtain by the aid of light an engraving of any subject drawn in
pen and ink or pencil unstumped. This method is important, as it is both perfect
and rapid, and enables the artist to work on a larger scale and with greater facility.
I obtain a sharp and vigorous negative of the original. I coat with bitumen one
of the smooth polished metal plates produced in the manner hereinafter described.
I expose and develop with spirits of turpentine; I then pass over the surface of
the print a brush charged with gum arabic acidulated with nitric acid. I then
wash quickly, dip the plate for a few seconds in a weak solution of mercurous
nitrate, again wash, and then silver the plate during a variable length of time, not
exceeding a few minutes. I then remove with benzine or ether the exposed
bitumen which forms the design, and dip the plate once or twice in a bath of
ammonio-mercuric sulphate for from 8 to 12 minutes, removing each time the
reduced mercury by the aid of heat, after which the plate is ready for printing
from. If in the course of the operation the silver coating has become altered at
any part, a solution of bitumen or engravers' varnish in benzine should be imme-
diately applied with a pad or cloth upon the dry plate, afterwards removing by

page_text: means of a piece of charcoal the bitumen in excess, none of which now remains
except that contained in the lines of the engraving which has been commenced.
The plate is then again dipped in the mercurous salt, washed, and resilvered, after
which it is dried, the bitumen removed by means of benzine or ether, and the
attack continued in the ammonio-mercuric bath.
(2nd.) Another and still more rapid means without the aid of light or of any
photographic apparatus may be employed. In this case the artist produces his
design either with a pen or greasy crayon upon lithographers' paper, which is then
transferred to one of the polished metal plates, and the transfer paper quickly
removed, leaving the design upon the phate, which is then washed, acidulated,
silvered, and engraved in a few minutes, as before described. Or instead of
drawing the design directly upon transfer paper, it may be drawn upon litho-
graphic stone, from which the necessary transfer prints are obtained for afterwards
producing engravings of the same size as the original.
(3rd.) Another method by which the most remarkable results may be obtained
by hands skilled in this kind of work is as follows:-One of the smooth polished
plates is silvered for less than a minnte, and placed in a box having intermediate,
frames of various sizes, similar to the boxes formerly used for iodizing daguerreo.
types. At bottom of this box is placed a porcelain dish containing loosely scattered
particles of sublimated iodine. The plate is placed with the silvered side down-
wards, and the box immediately closed. The plate is allowed to remain until the
silver assumes a saffron yellow color, which is easily known by practice; the plate
is then withdrawn and exposed beneath the negative of the original from which
the engraving is to be produced. This plate, which is fixed in a bath of hypo-
sulphite of soda, is a perfect positive print, which is then covered with a solution of
engravers' varnish in spirits of turpentine, in order to preserve all the transparency
necessary for the details of the picture. The latter is next to be put in the hands
of an operator, who simply traces the outline with a point, the size of which may
be varied. Having removed the thin coat of varnish and also the insensible layer
of silver by means of the point which slides upon the polished plate, as upon a
sheet of glass, the plate is then placed in the ammonio-mercuric bath before
mentioned for a few minutes, after which the engraving is ready for printing.
It will be evident that an artist may draw his picture or design directly upon
one of these polished silvered plates with a point, the design thus drawn requiring
but a few minutes to be converted into an engraving. The same method is
adopted for producing engravings on sheets of brass, as in the case of copper before
described.
To make "name plates," instead of biting in the letters by means of an ammonio-
mercuric bath, or a slightly acidulated solution of a copper salt, I dip them
immediately after the silvering and removal of the bitumen in a bath of ammonico
carbonate of copper, which forms the black parts of the design or inscription on the
silvered ground of the plate. To produce metallic relief surfaces for typographic
printing, I would observe that these photo chemical engraved surfaces are first
produced in intaglio, as before described, and when a sufficient depth has been
obtained, which is determined by experience, the engraved surface is lubricated
with a solution of 5 parts of olive oil in 100 parts of spirits of turpentine applied
equally with a brush, and then blackleaded. From this plate a counterpart in
relief is obtained in copper by electro-deposition, and finished either by mechanical
.or chemical means in the ordinary way.
I will next describe the manner in which I produce chemically pure metal
plates of varying thicknesses and with a perfectly plane and smooth surface, to be
employed in the processes of engraving, hereinbefore described.
Hitherto mechanical processes, which are both tedious and expensive, have been
employed for polishing metallic surfaces, and for levelling such surfaces. The
same remarks also apply to curved surfaces. All the objections to such processes
are avoided by this Invention, and a perfectly plain polished metal surface is
obtained at one operation. For this purpose I take a glass plate of suitable size

page_text: and silver it with an ordinary liquid, such as ammoniacal tartrate of silver, taking
care to thoroughly wash the silver deposit and dry the glass for some time at a
temperature of from 120° to 150° C. All these operations should be performed with
the greatest care, avoiding all contact of the fingers. The silvered glass plate is
then dipped in a galvanic bath, preferably in that hereinafter described, and imme-
diately put in connection with the positive pole. When the metallic deposit of
copper, silver, brass, iron, or other metal in solution has attained the desired thick-
ness, the metal readily separates from the glass, carrying with it the first layer of
silver deposited thereon. Great care should be taken with this first metal plate,
as it is to serve as the parent of the numerous other electrotype plates, which in
their turn serve for the production on a large scale of the objects to be manu-
factured for sale: The parent polished surface is next carefully rubbed with a pad
of cotton, fine linen, or leather dipped in a mixture of about 5 parts of olive oil
with 100 parts of spirits of turpentine, the reverse side being coated with wax,
fatty matter, or nonconducting varnish. In this condition the plate is dipped in a
galvanic bath (preferably of the kind hereinafter described) of the metal to form
the new plate or electrotype. In this way I can rapidly produce perfect copper
plates. By detaching the deposit which forms upon the parent plate, an indefinite
number of metallic plates may be obtained therefrom having the qualities before
indicated.
If such a high degree of polish and lustre is not required for the said plates, I
may employ the following means, by which perfectly plane sinooth surfaces are
also produced: The fusible metal before specified is poured as usual into the
mould, and; when it is perfectly clean; a glass plate, previously heated; if desired, is
applied upon it with slight pressure. The mass is then allowed to cool, and the
glass afterwards separated from the metal which thus forms the parent surface
which is dipped into the galvanic bath.
I employ, by preference, in the manufacture of the metallic plates à constant
galvanic bath, of which I will now describe the elements and action.
I use rectangular porous cells composed of two plates of porous earthenware,
charcoal, or other suitable material unattacked by acids, readily permeable by
liquids, and opposing the slightest possible resistance to the electric current, these
two plates (represented at a, b, c, d, and e, f, g, h, Figure 1) being furnished with
ribs or marginal perforations, and united by side pieces of guttapercha, wood coated
with varnish not attacked by acids, or a combination of these or other materials in
such inanner as to form a complete cell a, e, g, c, h, d, b, f, of which the two opposite
faces are porous and active.
Figure 2 represents the bath complete and ready for use; C, wood trough of
any suitable dimensions varnished on the outside and coated on the inside with
an acid resisting mixture of wax, resin, red ochre, and talc applied hot. The
trough contains the solution of the metallic salt to be decomposed to form the
electrotypes; c, c, c, four small gutta percha trays having perforated bottoms to
contain the salt to be dissolved as fast as the metal is deposited; these trays are
supported by their flanges upon the sides of the trough to which they are attached
by the copper clips a, a, a, a; B, metal rod bent downward at its two ends and
soldered to metal cross bars D, D, fixed to trough C, and separated therefrom by
small wood blocks n, n, upon which they bear, so as to insulate the metal as much
as possible from the bath; P, P, P, rectangular porous cells (or they might be
cylindrical) placed in the trough, in which are suspended, zinc plates hung, by
hooks 8, s, from the metal rod B, B. M, M, Mariotte's bottles bitubulated at bottom,
containing the acid liquid to be supplied to the porous cells through pipes T, T, T,
and having straight pipes R with cocks for regulating the flow of the liquid. For
this purpose it is simply necessary to charge the pipes T by blowing through
pipes R, and then closing the cocks until the desired rate of flow is obtained. Air
then enters and rises through the liquid at 0, 0, to replace the outflowing liquid.
The action thus being continuous. so long as any liquid remains in the bottles M,
M; M. t, t, t, are syphons hereinafter described, dipping down to the bottoms of

page_text: the porous cells, and discharging into a collecting pipe or longitudinal gutter G (of
glass, gutta-percha, or wood coated with gum lac) the overflowing acid liquid from
the bottles M, M, which is received in vessel V. The gutter G passes through and.
is cemented to the trough G, and is placed at such a level that the liquid in the
trough shall not rise as high as its upper edge, while the syphons t which discharge,
into said gutter leave sufficient liquid in the porous cells to ensure their proper.
action.
The syphon is constructed as shown in Figure 3, and consists of a glass tube t
dipping to the bottom of the porous cell P which is filled with the acid liquid to
the level ; the tube contains at its bend a vulcanised indiarubber tube a, b, to
which is fitted a small glass tube b, c, terminating in a point so as to render the
orifice c capillary. The advantage of this arrangement is that the numerous
bubbles disengaged during the action of the liquid in cell P on the zinc entering
more or less at the orifice O of pipe t would arrest its action, but as they cannot
enter at the capillary orifice c they lodge in the bend of the large tube t, whence they
escape freely without interfering with the syphon proper a, b, c, which thus acts
regularly and continuously, its action being moderated according to the levels n,n',
of liquid in the porous cell. As the internal syphon is free to move in the outer
tube it may occupy different positions, and so vary the level n of the liquid at
will. The trough is filled with a solution of the salt of the metal to be deposited,
and the trays c, c, are supplied with the same salt to maintain the strength of the
solution; the porous cells containing the acid liquid are placed in the trough, and
the zinc plates suspended in them at 8, 8; the small tubes t, t, are placed in
position; the pipes T, T, are charged and the flow regulated by cocks R, R, the
syphons t, t, being also charged by means of a small tube provided with an india-
rubber bulb. The circuit is then closed by immersing the moulds and suspending
them from the bars x, x, z, z, resting in notches made in cross bars D, D. This
galvanic bath or battery may also be readily transformed into an element of a two
fluid battery, as shown in Figure 4. Each element of the battery is formed of a
rectangular trough A, B, of dimensions suited to that of the porous cells; the
trough is lined with the same cement as in the former case, and to the upper
edges of the narrow sides A, B, are attached the two small guttapercha trays c, c,
having perforated bottoms in which is placed the salt for feeding the copper
solution of the battery; the two larger sides of the trough are coated with a
varnish of guttapercha in chloroform or benzine, which when dry is blackleaded
with a brush. The porous cell is placed in the trough and the zinc plate placed in
it with its two faces parallel to the blackleaded sides of the trough, the acid liquid
is then poured into the cell and the copper solution into the trough A, B. The
two poles of the battery are then connected in the usual manner, and the syphon
apparatus applied in the way before indicated. By acidulating more or less the
liquids employed for the battery and raising the surrounding temperature, the
galvanic action may be rendered more energetic, whilst always constant. The
copper which deposits continually upon the blackleaded surfaces of the trough
and forms the positive pole of the battery can be readily removed from time to
time.
To establish the initial current two small copper plates or wires united by a wire
with the positive pole should be applied upon the blackleaded surfaces. It will be
evident that the copper solution surrounding the porous cell may be replaced if
desired by bichromate of potash or nitric acid, as in the Bunsen cell, in which case
the copper plates of the positive pole would be replaced by two plates of carbon,
for example, united as before to form one pole so as to always utilise both sides of
the zinc plate for the production of the electric current. In all cases also the
syphon apparatus may be put in action for the renewal and withdrawal of the
liquids.
The Mariotte's bottles M, M, may also be replaced by a single reservoir com-
municating with a number of troughs. This modification is represented in
Figure 2bis, in which A is a reservoir of suitable dimensions containing the liquid

page_text: for the porous cells. B is a pipe made of lead, for example, for supplying a number
of troughs. The pipe is connected with reservoir A by an indiarubber pipe having
a clasp M, by which it is compressed to arrest the flow of acid. The pipe B is
provided with branches c, c, c, to which are connected indiarubber pipes d, d, d,
also fitted with clasps P, P. p, for regulating the flow to the porous cells, one of 5
which is placed opposite each of the branches.