AN IMPROVED PROCESS FOR PRODUCING PLATES FOR SURFACE PRINTING
Year: 1885

page_text: I, BENJAMIN CONSTANT LE MOUSSU of No 94 Boston Street, Manchester in the
County of Lancaster, Civil Engineer, do hereby declare the nature of my invention
for "AN IMPROVED PROCESS FOR PRODUCING PLATES FOR SURFACE PRINTING 39
and in what manner the same is to be performed to be particularly described and
ascertained in and by the following statement:-
My invention relates to the production of plates for surface printing, that is
to say with those parts in relief that are to receive the ink and to impress the
paper.
A process for the production of such plates was described in the Specification to
Letters Patent granted to me jointly with George Moore on the 18th July 1873
No 2474. As described in that Specification, a zinc plate was etched, the etched
out hollows were filled with fusible alloy and then by a second etching, the parts
of the plate other than those presenting the alloy were etched out leaving the alloy
in relief. There were practical difficulties in effecting this process. The drawing
of the design on the protected plate was difficult because the dark parts of the
design presented themselves light on the plate, and again the second etching was
difficult because the acid employed tended to eat under the alloy loosening or
detaching it. My present invention consists in a modification of the process
referred to whereby I am enabled to avoid the difficulties mentioned, rendering
the process practically available for copying photographs, drawings or prints.
In the first place I coat the zinc plate with a varnish which is photographically
sensitive; I prefer bitumen as it is usually applied for taking photographic
impressions. On the coated plate I place the subject to be copied it may be
a transparent photograph or a drawing or print on paper more or less translucent
or rendered so by applying wax, or the like substance. Exposing this to the light
I obtain on the bitumen an impression which, when developed and washed,
presents all the parts corresponding to the darks of the original as exposed parts
of the metal, those corresponding to the lights of the original remaining covered
by the protective coating of bitumen. I then subject the plate to the etching
action of dilute acid thus hollowing out the exposed parts corresponding to the
darks of the original; after cleaning off the bitumen, and washing and drying the
plate, I heat it and serve it with molten fusible alloy, composed preferably of lead
Dion 71

page_text: tin and bismuth. I work this into the hollows with a pad of fabric moistened with
chloride of zinc solution, and thus the alloy becomes soldered to the plate and into
the hollows thereof. After the alloy is set by cooling, I carefully scrape the plate
so as to uncover all the zinc surface and subject it to a second etching, whereby,
the alloy not being attacked by the acid, the zinc is hollowed out leaving the alloy
standing in slight relief. I now, with a roller, apply over the plate a fluid varnish
consisting preferably of bitumen and suet dissolved in turpentine. This, besides
coating the summits of the ridges of alloy, flows also down the sides of these ridges
giving them a protecting coating. I now subject the plate to a third etching and,
if necessary, to a repetition of the rolling with varnish and etching several times,
whereby the hollows are deepened, the ridges of alloy being left in good relief, and
held securely as the zinc on which they are based is not eaten away owing to the
protection given by the varnish. The plate is finally subjected to an acid bath
without any varnishing, and is thus ready for use as a forme for surface
printing.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that what
I claim is
The process for producing plates for surface printing by etching & photographic
impression on a zinc plate, serving the etched plate with fusible alloy, and again
etching repeatedly until the zinc is hollowed and the fusible metal stands in relief,
substantially as herein described.