Improvements in the Production of Lithographic Plates.
Year: 1897

page_text: Date o Application, 27th Mar., 1897-Accepted, 8th May, 1897
COMPLETE SPECIFICATION.
Improvements in the Production of Lithographic Plates.
I, SYDNEY PITT, of Sutton, in the County of Surrey, Gentleman, do hereby
declare the nature of this invention (which has been communicated to me from
abroad by the Société des Plaques Lithographiques, of 74 Rue Amelot, Paris, in
the Republic of France.) and in what manner the same is to be performed to
be particularly described and ascertained in and by the following statement :-
This invention has for its object a process for obtaining lithographic plategraphs
Lithographic plates prepared according to this invention have the advantage of
costing less than the lithographic stones in ordinary use; they are more easily
handled and yield excellent impressions.
The process consists in applying a suitable paste or covering to a suitable metal
or other plates.
In order to prepare the paste, crushed lithographic stone is treated with boiling
sulphuric acid in a stoneware pan upon a sand bath over a quick fire until it is
completely disorganized and has lost its carbonic acid.
Suitable proportions are two litres of sulphuric acid at 66° to 10 kilogrammes
of crushed lithographic stone.
When the lithographic stone has lost its carbonic acid consequent upon its
treatment with the sulphuric acid there is added to the mixture the following
composition also in a boiling state :-
Hydrochloric acid at 22°
Solid perchloride of iron
Manganese chloride
-
2 litres.
50 grammes.
50 grammes.
Care must be taken to dissolve these salts in the hydrochloric acid. A lively
effervescence is produced and a yellow greenish coloured mass is formed. It should
be continuously stirred.
When the effervescence is almost terminated and the mass (except certain
portions of unattacked stone) is reduced to a perfectly homogeneous paste, water
is added in small quantities in such a manner as not to drown the paste. It is
allowed to boil for an hour in order that the reaction may be completely terminated
and the transformation complete.
This semi liquid paste is then thrown into an earthenware vessel full of water.
After several hours this paste will be found deposited at the bottom of the
vessel; it is decanted and again washed with water. The washing is continued
until the wash water is completely neutral, that is to say until the supernatant wash
water no longer reddens blue litmus paper.
The paste is then drained aud pressed and is now ready to be employed in the
manufacture of plates as will be herein alter explained.
There is placed in an enamelled sheet iron vessel having a capacity of about
two hundred litres three kilogrammes four hundred grammes of paste prepared as
above, which has been diffused in ten litres of water.
There is then added whilst stirring five to six litres of water in which has been
dissolved 622 grammes of bicarbonate of soda.
The bicarbonate of soda has for its object to reconstitute a portion of the carbonate
of lime destroyed in the preparation of the paste and to eliminate the last traces of
acidity.

page_text: gramme.
The albumen and glue are dissolved in about 10 litres of water at 30° C.,
potassium silicate is then added and this mixture is poured, care being taken
to continuously stir, upon the bicarbonated paste in the vessel of 200 litres
capacity.
The albumen, glue and potassium silicate have the effect of giving adhesive
power to the composition.
The vessel is then filled with water, to which has been added 275 gramines of
liquid perchloride of iron giving colour to the mixture.
The composition is now ready to be applied upon the plates.
Before applying the composition upon the plates it is necessary to submit them
to a special preparation such as washing and then graining.
The sheets or plates of zinc or other metal of suitable dimensions are first
washed with a solution of hydrochloric acid at 2%. They are vigorously brushed
in order to well scour them, then washed with much water, sponged and steam
dried.
It is necessary to well dry the plates because water remaining oxidises them
and forms spots which it is almost impossible to remove without attacking the
metal.
Graining of the plates is effected as follows:-
An apparatus is made use of which will be easily understood without the aid of
a drawing.
This apparatus consists of a turbine fixed upon a vertical shaft rotated from
1000 to 2000 times a minute.
This turbine is fed at the top by a sand box, it is enveloped in a double cylindrical
casing.
The outer casing prevents loss of saud; the sand is brought to the sand box by
a bucket chain or otherwise. The inner casing upon which the plates are fixed
by means of screws or otherwise, receives a to and fro vertical movement in such
a manner as to present every part of the plates in front to the projection openings
of the turbine.
The speed of rotation of the turbine is dependent on the size of the sand
employed for graining.
The sand is forcibly projected onto the plates and gives them a grain corre-
sponding to the form and size of the sand grains or silex projected by the turbine.
The silex employed is of sizes differing according to the grain to be given to
the plates.
In certain cases one operation is not sufficient, and it is necessary to present the
plate several times to the turbine.
The plates thus grained are again washed with water, scoured with a solution of
hydrochloric acid at 2%, brushed to remove dust and any grains of sand which
may adhere there, de-acidified with a solution of bicarbonate of suda at 24%,
brushed, washed with water sponged and then immediately steam dried.
In this state they are ready to receive a layer of paste.
For this purpose they are placed in vessels open at the top to receive the
plates and interiorly heated to about 160° C. by means of steam introduced through
perforated tubes.
The liquid mass above described, carefully kept in continual agitation is projected
upon these plates heated to the temperature indicated.
Pulverizers or other analogous apparatus are employed for this purpose.
Consequent upon the high temperature of the plates at the monient at which the
liquid mass is projected upon them water is rapidly evaporated and the solid part

page_text: of the paste is deposited upon the plates. When a tenth of the liquid has thus.
been projected, the plate is drawn out of the vessel, washed with much water,.
brushed, again washed and carefully sponged.
This operation has for its object the removal of the solid particles only imper-
fectly adhering and which would prevent the successive layers from forming a.
homogeneous whole.
The plate is then replaced in the vessel and the operation repeated; and so on,
until all the liquid mass has been used.
Ten successive operations are generally needed.
A layer of about mm. thick is obtained. The plates are then steam dried,.
carefully wiped and stored in a dry place.
In certain cases plates having a grey tint cannot be employed, white plates may
be manufactured by proceeding as follows :-
Before projecting the successive layers of liquid matter upon the plates the
sheets serving as backing have applied to them three coatings of white con-
sisting of:
SYDNEY PITT..