Improved Photomechanical Process for the Production of Finished Plastic Casts.
Year: 1899

page_text: Date of Application, 25th Apr., 1899-Accepted, 17th June, 1899
COMPLETE SPECIFICATION.
Improved Photomechanical Process for the Production of Finished
Plastic Casts.
I, CARL PIETZNER, of 3, Mariakiferstrasse Vienna, VI in the Empire of
Austria, Imperial and Royal Court and Chamber Photographer, do hereby
declare the nature of this invention and in what manner the same is to be per-
formed, to be particularly described and ascertained in and by the following
statement;-
The effect produced by light on chromized glue films is well known. The
various processes heretofore adopted, by causing the light to act on chromate
glue layers for use in the production of plastic models, have given very un-
satisfactory results, because the reliefs thereby produced are only low-reliefs, i.e.
entirely flat reliefs having no material differences of surface elevation and there-
for unsuited for industrial purposes.
By my improved process which forms the subject of this application reliefs
are obtained for use as such, or for use in casting models for the most varied
industrial purposes and which give a true reproduction of the photographed
original as regards artistic execution and individual characteristics.
The improved process which is characterized by the results obtained, is nor-
mally carried out in the following manner:
Equal parts of agar-agar (an alga,-vegetable gelatine) and pure gelatine are
dissolved in water just sufficient to dissolve the two kinds of glue into a viscid
mass. This mass or substance is then mixed with a solution of 3% to 8%
chromate of potassium according to the light and shade effects of the original
(picture or body) which it is desired to photograph for sensitizing purposes and
is then applied as thick as possible to a smooth glass plate and dried with the
exclusion of light. The plates thus prepared are essentially suited for the pro-
duction of reliefs as they enable high reliefs of great resistance to be obtained
which are developed first in tepid water, then in warm water and finally in
water containing acetic acid.
From a negative photo taken in the ordinary manner from any desired
original is produced a positive high relief by causing the gelatin to swell
through the action of water thereon. From this positive a plaster of Paris cast
is taken which naturally must be negative and to which in the following I will
refer as the gypsum-matrice.
Again from the original there is produced a dia-positive and by means of
this a high relief which latter is therefore a negative from which a plaster of
Paris cast is made; this latter being a positive and hereinafter called the
gypsum die plate.
Thereupon a thin layer of plastic clay or other suitable material is prepared
and pressed into the gypsum matrice so as to obtain a positive cast. The gyp-
sum die-plate is now coated with shellac by preference, or other similar sub-
stance, and is afterwards corrected or touched up in accordance with the require-
ents of the art of plastic representation without however paying too minute

page_text: attention to a perfectly accurate likeness in every small detail of the original.
This touching up is done by raising the portions that are too low or too deep
by a covering with wax or similar tough but plastic substance, while scraping
the parts that protrude too much. The clay impression previously made by
the aid of the gypsum matric is then properly applied to the corrected gypsum
die-plate and gently pressed. This may also be effected by pressing the cor-
rected gypsum-die-plate on to the back of the clay impression contained in the
matrice so as to cause it to unite therewith or adhere thereto and afterwards
removing from the latter the clay together with the die-plate.
The clay impression thus transformed on to the gypsum die plate is now no
longer able to sink at those parts which in the first instance were too deep
because they are now resting upon the corrected die-plate. The combined clay
impression and die-plate is then finally finished and touched up in the usual
imanner.
The chief characteristic feature of this improved process consists in that a
gypsum die-plate the main features of which resemble the original and which
die plate is produced by any photographic or photomechanical means, and used
in combination with a second positive impression of clay or the like also taken
from the same original, for the purpose of enabling minute details of the
original to be reproduced and by this combination of the two parts to obtain
a true and faultless plastic representation of the said original.
A second method of carrying out the aforementioned process is as follows:
From a negative relief, produced by the aid of a dia-positive or by a gypsum
matrice prepared from a positive relief obtained from a negative impression,
there is produced a positive impression in a thin layer, the material used being
plastilin, a plastic commercial article much used by sculptors and resembling
wax or putty; or if desired wax may be used when moulding direct from the
original relief, while clay may be advantageously used for moulding from the
gypsum matrice.
The impression whether produced in plastilin or wax, or in clay by the one
or the other means is then by means of a moulding board worked and pressed
home as usual until the impression from an artistic point of view is fully equal
to the original and those parts which at first were too low are raised into their
proper position. If found necessary the cast may be retouched as in the first
process before described so as to produce an artistically finished plastic model
from which if desired a mould (matrice) may be taken to serve in casting or
otherwise forming the subjects or articles hereinbefore referred to required for
the various branches of the industries.
If the articles are made of ceramic ware they may if desired be produced in
a single or a number of colours burnt in during the firing.
Having now particularly described and ascertained the nature of my said in-
vention and in what manner the same is to be performed, I declare that what
I claim is:-
1. The process for the production of plastic models made from originals pro-
duced by photographic means from pictures or objects, characterized in that
a thin impression taken from the matrice is combined with a die plate and
which die plate as well as the matrice are either directly or indirectly produced
by the aid of two separate original reliefs obtained by photographic means and
whereby the die-plate is rendered true, in accordance with the rules of art, by
the application of wax or plastilin and by scraping, and that the impression or
cast taken from the matrice is then applied to the die-plate and touched up in
such a manner as to cause the relief model thereby produced to be plastic but
a true reproduction of the original in all its details, and which model can be
used in any manner but more especially for the moulding of metal or ceramic
reproductions in connection with any molten or plastic material generally.

page_text: 2. A process as claimed in Claim 1, characterized in that an original relief,
produced by photographic means, or a cast taken from the opposite original
relief is used for obtaining an impression in clay or other plastic material and
forming this impression into an exact copy of the photographic original by
working, pressing and lifting at the rear thereof and also if required touching
up the face portion in the usual manner.
3. A process as claimed in Claim 1 for the formation from ceramic material,
of objects in relief, characterized by the application thereto, after the moulding
of it, of an enamel colour or colours to be burnt in.
1 1000
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C.,
Agents for the Applicant.