IMPROVED PHOTOGRAPHIC ENGRAVING
Year: 1855

page_text: LETTERS PATENT to Alphonse Louis Poitevin, Civil Engineer, of Paris,
in the French Empire, for the Invention of "IMPROVED PHOTOGRAPHIC
ENGRAVING."
Sealed the 25th April 1856, and dated the 13th December 1855.
PROVISIONAL SPECIFICATION left by the said Alphonse Louis Poitevin
at the Office of the Commissioners of Patents, with his Petition, on the
13th December 1855.
I, ALPHONSE LOUIS POITEVIN, do hereby declare the nature of the said
Invention for "IMPROVED PHOTOGRAPHIC ENGRAVING " to be as follows:-
I pour or float upon a smooth plane surface (as, for example, a sheet of
glass,) a uniform film or layer of a solution of gelatine. The thickness of this
layer when dry should be proportionate to the height of the reliefs and the
depth of the hollows which it is intended to produce. After drying it, I plunge
it into a concentrated solution of bichromate of potash, or other salt of the same
acid,, provided that the base of the salt does not produce with gelatine a sub-
stance insoluble in water. After an immersion of some minutes, I remove it
and wash it slightly in water and again dry it. In lieu of drying the gelatine
before immersing it in the chromaté, it may be immersed as soon as it has set
and acquired sufficient firmness. In some cases I mix the solution of gelatine
and the bichromate before pouring it upon. the glass or other surface. The
layer of chromatized gelatine is exposed to the action of light in the camera
obscura, or in contact with a positive or negative photographic picture, or with

page_text: an engraving or other object which it is intended to reproduce. After a
sufficient exposure I plunge it in water; the parts which have not been acted
upon by the light absorb the water and swell or expand, while the parts which
have been acted upon by the light only become slightly moistened and form
hollows. Thus, the reliefs correspond to the darks and the hollows to the
lights.
A reverse mould or cast is taken in plaster of Paris or other plastic
material, or by means of the electrotype process, after first rendering the
surface a conductor of electricity. In taking a plaster mould, after swelling
the gelatine, as herein-before mentioned, I pour upon it a solution of proto-
sulphate of iron, and I afterwards wash it to remove the excess of protosulphate;
it is then surrounded with a frame of bars and the plaster is poured upon it.
When the plaster has set it is carefully removed. A great many good moulds
may thus be obtained, taking care to clean the gelatine after each operation,
and to treat it with the solution of protosulphate of iron, and to wash it in
plenty of water. The protosulphate of iron gives consistence and strength to
the plaster, some of the finer portions of which might otherwise be broken or
injured in separating the mould from the gelatine. In producing a mould by
the electrotype process, I metallize the surface of the gelatine, by impregnating it
(after swelling and drying, as herein-before described,) with a solution of iodide
of potassium or other iodide, or by immersing it after the exposure to light
in a solution, containing one-twentieth part of iodide of potassium, and after
draining off the excess of iodide I plunge it into a solution containing one-tenth
part of nitrate of silver. It is then exposed to light, and the iodide of silver
thus modified is reduced by a solution of protosulphate of iron. The surface
is thus covered with a film of silver, which is a conductor of electricity, and fit
for receiving the electro deposit. The proportions of the materials admit of
variation. From the plaster moulds I obtain metallio plates by the ordinary
stereotype processes or by the electrotype process. The plates obtained by either
process may be multiplied and reversed by the ordinary processes.
Thus, a direct or positive photographic or other picture produces an engraving
on gelatine, the reliefs of which correspond to the darks of the picture; and a
mould in plaster or a plate in copper is obtained from the gelatine with the
hollows corresponding to the darks, as required for printing in the manner of
ordinary copper-plate engraving. A reversed or negative picture produces an
engraving on gelatine in which the reliefs correspond to the darks of the nega-
tive, and consequently to the lights of the positive; and this gelatine yields a
reverse mould in plaster or in copper, in which the darks are in relief, as
required for printing in the manner of typography or wood engravings.

page_text: The engraved plates or surfaces thus produced are adapted for printing upon,
paper, cloths and other fabrics or materials, and also for embossing or stamping
card or paper or other suitable material, and also as moulds for earthen-
ware, porcelain, or other plastic substances, and for other purposes for which,
engraved plates or surfaces are required.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Alphonse Louis Poitevin in the Great Seal Patent Office
on the 7th June 1856.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, ALPHONSE
LOUIS POITEVIN, Civil Engineer, of Paris, in the French Empire, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Thirteenth day of December, in the year of our Lord
One thousand eight hundred and fifty-five, in the nineteenth year of Her
reign, did, for herself, Her heirs and successors, give and grant unto me, the
said Alphonse Louis Poitevin, Her special licence, that I, the said Alphonse
Louis Poitevin, my executors, administrators, and assigns, or such others as
I, the said Alphonse Louis Poitevin, my executors, administrators, and assigns,.
should at any time agree with, and no others, from time to time and at all
times thereafter during the term therein expressed, should and lawfully
might make, use, exercise, and vend, within the United Kingdom of Great
Britain and Ireland, the Channel Islands and Isle of Man, an Invention
for IMPROVED PHOTOGRAPHIC ENGRAVING, upon the condition (amongst others)
that I, the said Alphonse Louis Poitevin, my executors or administrators,
by an instrument in writing under my, or their, or one of their hands and
seals, should particularly describe and ascertain the nature of the said Inven-
tion, and in what manner the same was to be performed, and cause the same
to be filed in the Great Seal Patent Office within six calendar months next
and immediately after the date of the said Letters Patent.
NOW KNOW YE, that I, the said Alphonse Louis Poitevin, do hereby
declare the nature of the said Invention, and in what manner the same is
to be performed, to be particularly described and ascertained in and by the
following statement thereof, that is to say:-
I pour or float upon a smooth plane surface (as, for example, a sheet of
glass,) a uniform film or layer of a solution of gelatine. The thickness of this
layer when dry should be proportionate to the height of the reliefs and the

page_text: depth of the hollows which it is intended to produce. After drying it, I plunge
it into a concentrated solution of bichromate of potash or other salt of the same
acid, provided that the base of the salt does not produce with gelatine a' sub-
stance insoluble in water.' After an immersion of some minutes, I remove it and
wash it slightly in water and again dry it. In lieu of drying the gelatine before
immersing it in the chromate, it may be immersed as soon as it has set and
acquired sufficient firmness. In some cases I mix the solution of gelatine and
the bichromate before pouring it upon the glass or other surface. The layer of
chromatized gélatine is exposed to the action of light in the camera obscura, or
in contact with a positive or negative photographic picture, or with an
engraving or other object which it is intended to reproduce. After a sufficient
exposure I plunge it is water; the parts which have not been acted upon by
the light absorb the water and swell or expand, while the parts which have
been acted upon by the light only become slightly moistened, and thus form
hollows. Thus, the reliefs correspond to the darks, and the hollows to the
lights.
1
A reverse mould or cast is taken in plaster of Paris or other plastic material,
or by means of the electrotype process, after first rendering the surface a con-
ductor of electricity. In taking a plaster mould, after swelling the gelatine, as
herein-before mentioned, I pour upon it a solution of protosulphate of iron,
and I afterwards wash it to remove the excess of protosulphate; it is then
surrounded with a frame or bars, and the plaster is poured upon it. When
the plaster has set it is carefully removed. A great many good moulds may
thus be obtained, taking care to clean the gelatine after each operation, and to
treat it with the solution of protosulphate of iron, and to wash it in plenty of
water. The protosulphate of iron gives consistence and strength to the plaster,
some of the finer portions of which might otherwise be broken or injured in
separating the mould from the gelatine. In producing a mould by the elec-
trotype process, I metallize the surface of gelatine, by impregnating, it, after
swelling it with water and drying it, with a solution of iodide of potassium, or
other iodide, or by immersing it at once after the exposure to light in an
aqueous solution, containing one-twentieth part by weight of iodide of potassium,
and then after draining off the excess of iodide I plunge the gelatine into a
solution containing one-tenth part of nitrate of silver. The whole surface of
the gelatine is then exposed to light, and the iodide or other compound of
silver upon
or within its surface is modified or acted upon by the light, and is
afterwards reduced by a solution of protosulphate of iron. The surface is thus
covered with a film of metallic silver, which is a conductor of electricity, and
fit for receiving the electro deposit. The proportions of the materials admit of

page_text: variation. From the plaster moulds I obtain metallic plates by the ordinary
stereotype proceses.or by the electrotype.process. The plates or casts may by
multiplied and reversed by the ordinary processes.
Thus, a direct or positive photograph or other picture produces an engraving
on gelatine, the reliefs of which correspond to the darks of the picture, and a
mould in plaster or a plate in copper is obtained from the gelatine with the
hollows corresponding to the darks, as required for printing in the manner of
ordinary copper-plate engraving. A reverse or negative picture produces an
engraving on gelatine in which the reliefs correspond to the darks of the nega-
tive, and consequently to the lights of the positive; and this gelatine yields a
reverse mould in plaster or in copper, in which the darks are, in relief, as
required for printing in the manner of typography or wood engravings. When
the mould is taken in plaster, a second reverse plaster mould may be taken
from it, and used to produce a stereotype or electrotype plate. I find that the
chromatized gelatine is acted upon in the requisite manner by the light, as
herein-before described, without the addition to it of nitrate of 'silver, or other
salt of silver.
'
The engraved plates or surfaces thus produced are adapted for printing upon
paper, cloths, and other fabrics or materials, and also for embossing or stamping
card or paper or other suitable material, and also as moulds for earthenware,
porcelain, or other plastic substances, and for other purposes for which engraved
plates or surfaces are required. They may be employed in a flat, or curved,
or cylindrical form, as may be required.
Having now described the nature of my said Invention, and in what manner
the same is to be performed, I wish it to be understood that I do not claim
generally the application of gelatine and bichromate of potash to the purposes
of photographic engraving; but what I claim is,-
First, the application, in the process of photographic engraving in manner
herein-before described, of a plate of glass or other suitable surface coated with
a solution of gelatine, which is allowed to set or solidify, and is then (either
before or after being dried) immersed in or exposed to the action of a solution
of bichromate of potash, or other chromate whose base does not produce an
insoluble compound with gelatine.
Second, the application, in the process of photographic engraving in manner
herein-before described, of a plate or surface coated with a mixture of gelatine
and bichromate of potash, or other suitable chromate, or first coated with
gelatine, and then exposed to the action of the bichromate of potash or other
suitable chromate, in either case without the addition of nitrate of silver.
Third, the application of a solution of protosulphate of iron to the surface of

page_text: the photographic gelatine engraving before pouring the plaster upon it in the
process of taking a plaster cast from the gelatine, as herein-before described.
Fourth, the mode, herein-before described, of metallizing the surface of the
gelatine before submitting it to the electrotype process.
In witness whereof, I, the said Alphonse Louis Poitevin, have hereunto
set my hand and seal, this Second day of June, in the year of our Lord
One thousand eight hundred and fifty-six.
Witness,
CH. ARMENGAUD, Ing" Civil,
6, Rue Filles du Calvaire, à Paris.
A. L. POITEVIN. (L.B.)