IMPROVEMENTS IN CHEMICALLY ENGRAVING COPPER OR ZINC SURFACES
Year: 1882

page_text: LETTERS PATENT to Thomas Ruddiman Johnston, of Edinburgh in the
County of Midlothian North Britain for an invention of "IMPROVEMENTS IN
PROVISIONAL SPECIFICATION left by the said Thomas Ruddiman Johnston
at the Office of the Commissioners of Patents on the 13th May 1882.
THOMAS RUDDIMAN JOHNSTON, of Edinburgh, in the County of Midlothian,
North Britain, " IMPROVEMENTS IN CHEMICALLY ENGRAVING COPPER OR ZINC
SURFACES,"
This Invention relates to improvements in chemically engraving copper or zinc
surfaces such as plates for the production of maps, plans, pictures, and in general
such work as is now produced with the graver, or with the etching needle and
etching fluid. It is also applicable for engraving copper printing cylinders such as
are used in calico printing and analogous operations.
In carrying out the Invention I take from a lithographic stone or from a zinc
plate by means of a lithographic press, an impression in greasy ink on what is
called "Scotch re-transfer paper," that is to say paper which is coated with Plaster
of Paris and paste.-This is simply called in "Lithography" taking a re-transfer.
This impression I transfer to a chemically clean copper or zinc plate, by means of
a lithographic or copper-plate press, having first slightly damped either the plate
or the transfer.-If the transfer is made to a zinc plate I may slightly grain its
surface with pumice powder.-The back of the transfer is then damped, and when
the paper has absorbed the moisture it is removed, and the plaster composition
being carefully rubbed with a wet sponge comes off, leaving the greasy impression
on the plate. The plate is then dried, and a weak solution of gum is rubbed
gently backwards and forwards over its surface, after which a larger quantity is
Hoated over it to remove any air-bells or blebs which may have been formed
thereon. The plate is then allowed to dry, and when dry the greasy ink is
washed out with rectified spirits of turpentine, when the plate is left bare where

page_text: the greasy impression was, and on all other parts is covered with a thin film of
gum. A solution of Perchloride of iron in alcohol is then poured on the plate and
this etches it without attacking the ground.-Washing in water removes the gum
and leaves an etched plate.
Isinglass, albumen, or any substance soluble in water and insoluble in alcohol
and that is repellent of grease may be used instead of gum.-Instead of taking an
impression as herein before set forth, from a lithographic stone, or from a zinc plate,
drawings in a greasy ink may also be made direct on the plate instead of transferred
thereto and afterwards treated in a similar way or transfers may be taken from
type or any substance capable of yielding a transfer in greasy ink.
When using my Invention for chemically engraving on cylindrical surfaces, I
use the equivalent of a lithographic or copper-plate press, for transferring the
impression thereto.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Thomas Ruddiman Johnston in the Great Seal Patent Office on
the 11th November 1882.
THOMAS RUDDIMAN JOHNSTON of Edinburgh in the County of Midlothian,
North Britain "IMPROVEMENTS IN CHEMICALLY ENGRAVING COPPER OR ZINC
SURFACES
13
My said Invention relates to improvements in chemically engraving copper or
zinc surfaces such as plates for the production of maps, plans, pictures, and in
general such work as is now produced with the graver or with the etching needle
and etching fluid. It is also applicable for engraving copper printing cylinders
such as are used in calico printing and analogous operations.
In carrying out. the Invention I take from a lithographic stone or from a zinc
plate by means of a lithographic press, an impression in greasy ink on what is
called "Scotch retransfer paper" that is to say paper which is coated with plaster
of Paris and paste. This is simply called in "Lithography" taking a retransfer.-
This impression I transfer to a chemically clean copper or zinc plate by means of a
lithographic or copper-plate press, having first slightly damped either the plate or
the transfer. If the transfer is made to a zinc plate I may slightly grain its
surface with pumice powder.-The back of the transfer is then damped and when
the paper has absorbed the moisture it is removed, and the plaster composition
being carefully rubbed with a wet sponge comes off leaving the greasy impression
on the plate. The plate is then dried and a week solution of gum arabic slightly
alkalized is rubbed gently backwards and forwards over its surface, after which a
larger quantity is floated over it to remove any air-bells or blebs which may have
been formed thereon.-The strength of the gum solution which I have found most
desirable is as follows:
For copper, Gum Arabic 1 oz to 19. oz: Water.
For zinc, gum arabic 1 oz to 15 oz: Water.
The plate is then allowed to dry and when dry the greasy ink is washed out with
rectified spirits of turpentine, when the plate is left bare where the greasy
impression was, and on all other parts is covered with a thin film of gum.--A
solution of Perchloride of iron in alcohol is then poured on the plate and this
etches it without attacking the ground. The strength of the etching solution
which I have found generally most desirable is as follows:
1 oz:
Dry Perchloride of Iron in 4 fluid oz: Alcohol.
but this etching solution can be used with more or less Perchloride if the transfer
originally on the plate was composed of thick lines or thin ones.-Washing in
water removes the gum and leaves an etched plate.
Isinglass, albumen, or any substance soluble in water and insoluble in alcohol,
and that is repellant of grease, may be used instead of gum.-Instead of taking an
impression as hereinbefore set forth, from a lithographic stone or from a zinc plate,
drawings in a greasy ink may also be made direct on the plate instead of transferred
thereto and afterwards treated in a similar way, or transfers may be taken from
type or any substance capable of yielding a transfer in greasy ink.
When using my Invention for chemically engraving on cylindrical surfaces, I use
the equivalent of a lithographic or copper-plate press for transferring the impression
thereto.
By my improved process anything already drawn on stone, or transferred to
stone, or wood-engravings, or type, can, by simply taking an impression and
without the aid of photography, be converted into an engraved plate, and I would

page_text: also observe that an essential feature in the working of the process consists in
coating a plate with a certain strength of gum that will stand the etching solution
and yet be not so thick as to crack in drying or prevent the greasy ink from being
removed.
Having now described and particularly ascertained the nature of my said
Invention and the system mode or manner in or under which the same is or may
be used or practically carried into effect I would observe in conclusion that what I
consider to be novel and original and therefore claim as the Invention secured to
me by the hereinbefore in part recited Letters Patent is:
The combined process of chemically engraving copper or zinc surfaces substantially
as bereinbefore described.
In Witness Whereof I, the said Thomas Ruddiman Johnston have hereunto
set my hand and seal this tenth day of November in the year of Our
Lord One thousand eight hundred and eighty-two.
T. RUDDIMAN JOHNSTON
(I.S.)