An Improved Method of Preparing Metallic Plates for Lithography
Year: 1892

page_text: Date of Application, 9th July, 1892-Accepted, 19th Nov., 1892
COMPLETE SPECIFICATION.
An Improved Method of Preparing Metallic Plates for Lithography,
I, HUGO BITTNER, of 24 Rue de l'Evêque Brussels, in the Kingdom of
Belgium, do hereby declare the nature of this invention 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 a method of preparing metallic plates for lithography.
The continually increasing rarity of lithographic stones, their high price, the
encumbrance caused by their employment, have given rise to the idea of
substituting for them metallic plates which are less encumbering and especially
lower in price.
But up to the present time the results obtained have not been satisfactory,
because these plates were obtained by dry methods which give brittle and defective
surfaces; moreover, special apparatus were required so that corrections of the plates
were impossible.
My improved method differs from those heretofore employed in that I operate by
the humid way; that I may employ any metals, although the metal which gives
the best results is an alloy of zinc and tin made in the proportion of two-fifths of
tin and three-fifths of zinc; that, after the plate has been prepared, any-one in the
trade is able to make corrections and employ the plate again like a stone; that the
preparations used on my plates are homogeneous and essentially elastic which
renders them suitable for working by rotary machines.
According to my invention a plate of any metal is cleansed by any suitable
process to remove the layer of oxide which covers it. Then I coat this plate by
immersing it in a bath formed of a soluble silicate and albumin which are
mixed in proportions varying with the work to be done with the plates, these
proportions being preferably silicate 335 grammes albumin 12 grammes and water
1000 grammes.
The presence of albumin in this bath has for its object to render the silicate
absolutely adherent and at the same time quite elastic, so that the plate may be
bent in any direction without causing either a rising or fracture on its surface.
When removed from this bath 1 immerse the somewhat dried plate in a second
bath composed of water 100 grammes and nitrate of lime 2 grammes; after some
minutes withdraw it from this bath, wash it and immerse it in a preparation
composed of limewater to which sulphuric acid and phosphoric acid are added in
proportions varying with those of the two preceding baths.
These proportions are as follows:-Lime water 1000 grammes, sulphuric acid
from 3 to 15 grammes, phosphoric acid from 2 to 10 grammes. The proportions
of this bath may be varied according to the size of the grains of the plate.
In these operations an absolutely insoluble silicate of lime is formed in the body
of the plate, and the soluble base of the original silicate combines with the free
sulphuric acid and passes into the bath.
The phosphoric acid here exerts an action which is absolutely necessary for the
success of the operation.
After a washing I let dry and obtain a plate upon which I work as on a litho-
graphic stone, and by which I can achieve much better results both as regards the
quality and the number of the prints than those which are obtained by means of a
stone; whilst, moreover, retouching is possible on them.
The plate thus prepared enables a drawing or a transfer to be indefinitely
preserved. It permits of printing in black according to ordinary processes; for
printing in colours the composition of the inks must be modified so as to avoid
chemical reactions on the surface of the metal.

page_text: Having now particularly described and, ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
...
First. The preparation, by the humid method, of metallic plates for rendering
them suitable for lithographic printing, which consists substantially in coating the
cleansed plate with a soluble silicate mixed with albumin, then precipitating this
silicate into the body of the plate by a bath of nitrate of lime and next by a second
bath, in order to complete this preparation by means of lime mixed with sulphuric
acid and phosphoric acid.
Second. In the preparation of metallic plates for lithography the employment of
two precipitating baths composed substantially as herein described..
Third. The employment of metallic plates prepared substantially as herein
described.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, Agents for the Applicant.