IMPROVEMENTS IN ENGRAVING
Year: 1854

page_text: LETTERS PATENT to Theobald Denny, of Strasbourg, in the Empire of
France, and of 4, South Street, Finsbury, London, Engraver, for the
T...
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1
PROVISIONAL SPECIFICATION left by the said Theobald Denny at the
Office of the Commissioners of Patents, with his Petition, on the 28th
February 1854.
I, THEOBALD DENNY, of Strasbourg, in the Empire of France, and of 4,
South Street, Finsbury, London, Engraver, do hereby declare the nature of
the Invention of "IMPROVEMENTS IN ENGRAVING" to be as follows:-
My Invention consists in first covering a plate of polished steel with a
coating of caoutchoux dissolved in naptha, pyroligneous ether, or other suitable
solvent; this is then blackened, by passing it over an ignited match or wick
saturated with spirits of turpentine; I next heat the plate underneath till its
oxidation gives it a blueish white color; this operation dries the coating on its
upper surface, and permits of its being drawn upon. The drawing is then
etched with a fine point upon the coating so formed, & moistened with a
solution of virgin wax in naptha, after which it is rubbed off with wadding
cotton; I next plunge the plate for two seconds into a bath of distilled water,

page_text: holding in solution cyanide of potassium, together with a small quantity of
tannin, sulphate of copper, and caustic potash, connect it forthwith with the
conductor of the positive pole of a galvanic battery, & put it again into the
bath, where an electrode of good red copper or platium is placed in com-
munication with the other pole.
The coppering of the drawing occupies two hours; after which the plate is
cleaned with alcohol. The design now transferred to the copper is then silvered
by the following means (it may also be gilded):-The plate is plunged into a
bath containing cyanide of potassium, the yellow ferrocyanide, a little tannin,
& oxide of silver. The steel plate connected with the positive pole of the
battery should be placed near an anode of pure silver; the silver is thus
precipitated on the copper parts; the plate is then withdrawn & cleaned. The
plate is slightly heated, & I pour on it a few drops of colophone dissolved in
petroleum or other solvent, which I evaporate till the matter is solidified; I
I then spread wax over all the portions of the drawing, & which, melting,
prevents the colophane from adhering; this process is repeated two or three
times, & after the plate is cooled it is cleaned with wadding cotton.
The plate is finally placed in a concentrated solution of sulphate of copper
and sal ammoniac, communicating by a conductor with the anode of the
negative pole, and to the positive pole is fixed a clean plate of copper, eight
times larger than the engraved plate, to eat into the parts where the steel is
exposed. I can employ a vessel divided into two by a porous partition, filling it
on the engraved side of the plate with solution of sulphate of iron & sal-
ammoniac, and on the other with sulphate of iron only; the copper plate is
changed whenever, it is covered with iron. The engraved plate is left exposed
till the required thickness is attained, and the parts of it which are not so thick
preserved, by covering them with colophony dissolved in petoleum or other
solvent. I operate by analogous processes for making the engraving on plates
of other metals, making use of the solutions of salts containing them.

page_text: WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Twenty-eighth day of February, in the year of our Lord
One thousand eight hundred and fifty-four, in the seventeenth year of Her
reign, did, for Herself, Her heirs and successors, give and grant unto me, the
said Theobald Denny, Her special license that I, the said Theobald Denny, my
executors, administrators, and assigns, or such others as I, the said Theobald
Denny, my executors, administrators, and assigns, should at any time agree
with, and no others, from time to time and at all times thereafter during the
term therein expressed, should and lawfully might make, use, exercise, and
vend, within the United Kingdom of Great Britain and Ireland, the Channel
Islands, and Isle of Man, an Invention for "IMPROVEMENTS IN ENGRAVING,"
upon the condition (amongst others) that I, the said Theobald Denny, by an
instrument in writing under my hand and seal, should particularly describe
and ascertain the nature of the said Invention, and in what manner the same
was to be performed, and cause the same to be filed in the Great Seal Office
within six calendar months next and immediately after the date of the said
Letters Patent.
NOW KNOW YE, that I, the said Theobald Denny, do hereby declare the
nature of my said Invention, and in what manner the same is to be performed,
to be particularly described and ascertained in and by the following statement
thereof, that is to say :-
My Invention consists in an improved mode of producing engravings on
metallic plates suitable for ordinary surface printing.
I will now proceed to describe the several processes to be employed for
carrying out my Invention. I take, by preference, a plate of polished steel, on
account of its homogeneous texture and hardness, and cover it with a coating of
caoutchouc dissolved in petroleum, pyroligneous ether, or other suitable solvent.
The plate is then passed over the flame of a cotton wick, burning spirits of
turpentine. The smoke black that is given off mixes with the caoutchouc
coating, and effects the blackening of the surface of the plate. I then pass
over the plate a few drops of the said caoutchouc solution to moisten the dry
parts, taking care to well mix it with the smoke black, to prevent the adhesion
to the plate. I then make the surface as even as possible. For that purpose,
during the heating process, I place the plate with the caoutchouc upon another
fixed plate and dry the caoutchouc. I heat the plate underneath in a regular
manner to oxidation, until it acquires a blueish white or white color, which
causes the caoutchouc coating to adhere firmly to the oxide of iron, and form
with it a solid body. By this means I obtain a smooth and hard surface, upon

page_text: which the required design is to be lightly drawn with a lead pencil without
removing the coating.
The design thus prepared is etched with etching needles of the required sizes,
which remove the coating on the plate, and leave uncovered the oxide of the
metal without incising the plate. Lines of every description and fineness, dots
and cross hatchings, may be produced by this means. A solution of virgin wax
and petroleum is passed over the plate, and immediately cleaned off with dry
cotton wadding, so as to leave the etched parts damp. The oxidized metal
exposed remains unchanged, but the caoutchouc coating assumes a glossy
appearance and increases in size, thus forming a relief.
The caoutchouc absorbs the solution of wax and petroleum, which has the
effect of preventing the electric current developed in the copper bath into which
the plate is afterwards plunged from acting immediately on the oxidized part
underneath the caoutchouc coating. I now plunge the plate for about two
seconds into a bath composed as follows; videlicet, I dissolve about one ounce
(troy) of cyanide of potassium, at a temperature varying between one hundred
and forty degrees and one hundred and eighty degrees Fahrenheit, in about
one quart of distilled water, adding one-fortieth of an ounce of tannin. I
saturate the solution with sulphate of copper, and allow the whole to cool;
I cause an electric current to pass through, and then add caustic potash, until
the mixture assumes a dark blue color. This bath should be employed in the
cold state.
After withdrawing the plate I plunge it again into the bath, to remove any
air bubbles remaining on the etched parts of the plate, and when this is effected
I connect the plate with the conductor of the positive pole of a galvanic
battery, and I place at about two inches above and facing the plate an annode
or electrode, made of good red copper or platinum, having its conductor in
communication with the negative pole. The complete and perfect coppering
of the drawing usually occupies two hours; after which the plate is cleaned
with alcohol, oxide of iron, or with any other similar means, to remove the
coating. In order to give greater strength and relief to the coppered engraving
it should be silvered. The silvering bath is thus composed; videlicet, I dissolve
about half an ounce, troy, of cyanide of potassium, heated to between one
hundred and forty degrees and one hundred and eighty degrees Fahrenheit, in
about one quart of distilled water, and add about one ounce ferrocyanide, one-
fourtieth of an ounce of tannin, which I saturate with oxide of silver free of
acid. This bath is also to be employed in the cold state. The plate is plunged
into this bath, and set at about two inches distance from the anode, which

page_text: should be of pure silver. The coppered steel plate being connected with the
positive pole of the battery, and the electrode with the negative pole, the silver
is thus precipitated evenly on the coppered parts, that is to say, on the design,
in uniform thickness, but only as a metallic powder on the steel. The plate is
then withdrawn, and cleaned with cotton wadding and alcohol, to remove the
metallic powder. I afterwards slightly heat the plate with spirits of wine, or I
pour on it a little colophony dissolved in petroleum or other solvent, which,
when spread over the engraving, I cause to evaporate, by heating it till the
matter is solidified; I pass virgin wax over the design, which melts instan-
taneously, and which the dissolved colophony prevents from adhering to the
plate. This operation is repeated two or three times, and the plate being
cooled, is cleaned with cotton wadding, whilst the wax is still liquescent, to avoid
using alcohol or other solvent. The plate is finally exposed to the action of an
electric current in a concentrated solution composed of two parts, sulphate of
iron and one part sal ammoniac, in order to have the parts of the plate where
the steel is exposed bitten out. I attach the steel plate by means of a conductor
to the negative pole of the battery, and I fix a well-scoured plate of copper to
the positive pole. The positive pole should be about eight times larger than
the anode, or of the plate to be engraved. In order to accelerate the operation,
and to render it more perfect, I can employ a trough divided into two parts by
a porous partition, filling the division of the trough containing the engraved
plate with a solution composed of two parts of sulphate of iron, one part of sal-
ammoniac, with an equal volume of distilled water, and filling the other side of
the partition, that is to say, on the side of the positive pole, a highly con-
centrated solution of sulphate of iron, taking care to change the copper plate
whenever it gets covered with oxide of iron. The solution to be used must be
pure and neutral, and weakened by water, as it is the electric fluid with the
solution composing the bath, and not any free acid, that has to bite out the plate.
The engraved plate should be left exposed to the action of the bath till the
required depth is attained, and the other parts are covered over with colophony
dissolved in petroleum or other solvent. The silver and copper coatings are
then removed, rubbed down, and I expose for a minute or two the steel plate
(it being attached to the anode with its engraved surface facing the positive
pole) to the action of the battery in the bath of sulphate of iron and sal-
ammoniac, in order to remove the polish and lustre of the engraved surface, so
as to allow the printing ink to lay well.
Other metals, such as copper, zinc, antimony, gold, silver, or platinum, may
be employed for making engraving plates according to the above described

page_text: And having now described the nature of my said Invention, and the manner
of performing the same, I wish it to be understood that I do not confine
myself to the precise details herein laid down, so long as the peculiar character
of my Invention be retained. But what I claim as new, and intended to be
protected by the said in part recited Letters Patent, is,-
The processes herein described for producing an engraving surface upon
metallic plates applicable to surface printing.
In witness whereof, I, the said Theobald Denny, have hereunto set my hand
and seal, this Twenty-fourth day of August, in the year of our Lord
One thousand eight hundred and fifty-four.
Witness,
HY GILBEE.
T. DENNY. (L.S.)