IMPROVEMENTS IN PRO- DUCING PRINTING AND OTHER IRREGULAR SURFACES BY THE AID OF PHOTOGRAPHY
Year: 1860

page_text: PROVISIONAL SPECIFICATION left by Leopold Eidlitz at the Office
of the Commissioners of Patents, with his Petition, on the 9th April
1860.
I, LEOPOLD EIDLITZ, of New York, United States of America, Architect, do
hereby declare the nature of the said Invention for "IMPROVEMENTS IN PRO-
DUCING PRINTING AND OTHER IRREGULAR SURFACES BY THE AID OF PHOTOGRAPHY,"
to be as follows:-
The subject of my Invention is an improved method of preparing by the
aid of photography the moulds upon which a metallic deposit is to be made
by the electro-metallurgical process, and my Invention consists in the use
or employment of a chemical agent having the property of being rendered
insoluble in water by exposure to the action of light, and in combination
therewith a substance which is more or less expansive under the influence of
moisture.
The chemical salt which I prefer to employ is the bi-chromate of potash,.
and I have discovered that when gelatine (which when dry is capable of being.
expanded by the action of water) is impregnated with the said salt and submitted
to the action of light in an ordinary photographic printing frame, it becomes.
differently affected by the different degrees of light which fall upon its surface

page_text: consequent upon the lights and shades of the negative employed, and that this
difference can be relied on to occur with such accuracy, that when the gelatine
is afterwards exposed to the action of moisture, elevations and depressions
corresponding exactly in degree with the lights, shadows, middle tints, and
their most delicate variations of the photographic negative will be developed
upon it.
The manner in which I avail myself of this property is as follows:-I make
a solution of the bi-chromate of potash in distilled water, and although in some
cases a saturated solution may be found necessary, one of less strength will
generally be preferable. This is to be carefully filtered, and then I dissolve in
it pure gelatine in the proportion of, say, 1 oz. of gelatine to 10 oz. of the
solution. This dissolving may be effected in a hot water bath, but all of the
process is performed in a darkened room, and the mass is preserved for use in
a dark place also. When to be used, the vessel containing it may be heated
in the bath, and the mixture is then poured upon a sheet of glass or other
suitable substance in such quantity that when dry it will form a thin film.
The drying may be effected by simple exposure to the air in a hot and dark
room, and when properly dried the edges of the plate should be coated with
varnish. The plate is now to be put into the printing frame under a
photographic negative, and in a short time the surface of the plate will become
of a brown colour, when it should be removed and immersed for about 5
minutes in a bath of cold water. The effect of this will be that where the
lights were strongest the gelatine will have been rendered incapable of being
expanded by the action of the water, while where the shades were deepest the
amount of that expansion will be greatest, and this difference will be on all
parts of the plate just as the plate at each part has been exposed to more or
less light. The plate may now be immersed in a solution of sulphate of
copper in water, being left in this for some little time. It is then to be
washed in cold water, and dried until the water is removed from the surface,
though below it will still be moist. The mould being thus prepared, is now
coated with a metallic substance, in order that it may receive the deposit of
metal when in the precipitating trough; and this I effect by pouring upon it
a solution of chloride of gold, allowing this to remain for about one minute
then permit the surface to dry again until all visible moisture is removed from
it. The plate is now exposed to the fumes of phosphorous dissolved in
sulphuric ether, and when again dried it will be seen to be covered with
metallic gold. It is now ready for the deposit of the copper or other metal
upon it. When removed from the trough, the glass will readily separate from

page_text: the gelatine, and that may be washed off, using warm water and a soft
brush.
If the plate is to be used for letter-press printing, a positive photograph
should be employed in the printing frame, or a cast in wax may be taken
from the gelatine plate, and the metal be deposited upon that. An engraving,
manuscript, or letter-press work may be employed in the printing frame instead
of the photographic negative or positive.