An Improved Process for Depositing Metals on Silver Coatings.
Year: 1896

page_text: Date of Application, 6th May, 1896
Complete Specification Left. 8th Feb., 1897-Accepted, 6th May, 1897
PROVISIONAL SPECIFICATION.
An Improved Process for Depositing Metals on Silver Coatings.
We, THE IMPROVED ELECTRIC GLOW LAMP SYNDICATE, LIMITED, of
1, Arundel Street, Strand, in the County of London, do hereby declare the nature
of this invention (a communication to us by Carl Schwabe, of 70 Blumenstrasse,
Berlin, in the German Empire, Manufacturer) to be as follows:-
This invention relates to an improved process for depositing metals on silver
coatings.
In depositing copper on silver coatings which have been obtained on glass or
other transparent bodies by reducing a silver solution, the disadvantage is
experienced in using the ordinary copper baths that the silver together with the
copper deposited on it becomes separated in the form of flakes or scales from the
supporting body of glass or other material. The same thing occurs whether acid
copper baths or baths of the double cyanide of potassium and copper be used for
producing the deposit of copper.
In order to overcome this disadvantage careful researches and experiments
have been made with such silver coatings. From these experiments it has been
ascertained that remains of the silvering solution are found in the pores of the
silver coating and even between the silver and the glass itself, and, moreover,
that the silver layer or coating resembles physically a stretched skin so that if by
any means the equilibrium of the stretching forces is disturbed the silver skin is
torn. It has also been shewn that both acids and acid salts or cyanide of potassium,
which materials decompose such silvering liquids, produce injurious effects on the
silver skin by setting up chemical reactions which take place in the interior of
the silver skin and between the said skin and the glass.
The above considerations explained why a silver coating, which was immersed
in the usual acid bath for the deposition of copper thereon, was torn and partially
or wholly separated, together with the copper deposited on it, from the glass or
other support. A similar result was obtained by using baths of the double cyanide
of potassium and copper.
In the chemical reaction which takes place between the remains of the original
silvering liquid, existing in the silver coating and between the silver coating and
its support, and the constituents of the metal bath, the liquid particles are set in
motion and these movements, together with changes of condition, evolution of
heat, etc. cause the silver skin to become torn.
The above statements are supported by the observation that a drop of dilute
sulphuric acid placed on a silver coating produced by the reduction of an
ammoniacal silver solution tears the said silver coating around the drop of
Not only do
sulphuric acid, the silver coating being considerably contracted.
baths for depositing copper act in this way but the same results are obtained with
baths for depositing other metals.
According to our invention we effect the deposition of other metals on silver
coatings as follows, that is to say, we prevent the mutual reaction between the
constituents of the bath and the substances enclosed in the interior of the silver
during the preceding process of obtaining the silver coating. Experiment has
further shewn that such a process for depositing metal on silver coatings can be

page_text: carried out advantageously by adding to the metallic bath the remains of the
silvering solution or the essential constituents of the same or substances which
produce an analogous result, that is to say, which cause the reactions or decom-
positions, that would otherwise be set up in the silver coating by the metal bath,
to previously take place in the said metal bath itself.
By this method of carrying out the above described process it is only necessary
to add to the metal bath, which may be for instance a copper or a gold solution
or a solution containing any other metal to be deposited on the silver coating,
sufficient of the silvering fluid or of its active elements or of an analogously acting
substance to prevent any reaction taking place between the metal bath and the
substances present in the silver coating. The proper quantities can be ascertained
by a preliminary experiment. The bath is then ready for depositing its metal on
the silver coating.
Dated this 6th day of May 1896.
G. F. REDFERN & Co.,
4, South Street, Finsbury, London, Agents for the Applicants.
A communication from abroad by CARL SCHWABE, of 70 Blumenstrasse, Berlin,
in the German Empire, Manufacturer.
We, THE IMPROVED ELECTRIC GLOW LAMP SYNDICATE, LIMITED, of,
97 Queen Victoria Street, London, E.C., but formerly of 1 Arundel Street
Strand, in the County of London, 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 :-
This invention relates to an improved process for depositing metals on silver
coatings.
In depositing copper on silver coatings which have been obtained on glass or
other transparent bodies, such as bulbs of incandescent lamps, by reducing a silver
solution, the disadvantage is experienced in using the ordinary copper baths, that
the silver, together with the copper deposited on it, becomes separated in the form
of flakes or scales from the supporting body of glass or other material. The same
thing occurs whether acid copper baths or baths of the double cyanide of potassium
and copper be used for producing the deposit of copper.
In order to overcome this disadvantage careful researches and experiments have
been made with such silver coatings. From these experiments it has been
ascertained that remains of the silvering solution are found in the pores of the
silver coating, and even between the silver and the glass itself, and, moreover, that
the silver layer or coating resembles physically a stretched skin, so that if, by any
means, the equilibrium of the stretching forces is disturbed, the silver skin is torn.
It has also been shown that both acids and acid salts or cyanide of potassium,
which materials decompose such silvering liquids, produce injurious effects, on the
silver skin, by setting up chemical reactions, which take place in the interior of
the silver skin and between the said skin and the glass.
The above considerations explained why a silver coating, which was immersed
in the usual acid bath for deposition of copper thereon, was torn and partially, or
wholly, separated, together with the copper deposited on it, from the glass or other
support. A similar result resulted by using baths of the double cyanide of
potassium and copper.

page_text: In the chemical reaction which takes place between the remains of the original
silvering liquids, existing in the silver coating and between the silver coating and
its support, and the constituents of the secondary metal bath or the secondary
coating, the liquid particles are set in motion, and these movements, together
with changes of condition, evolution of heat, etc., cause the silver skin to become
torn.
The above statements are supported by the observation that a drop of dilute
sulphuric acid placed on a silver coating, produced by the reduction of an
ammoniacal silver solution, tears the said silver coating around the drop of
sulphuric acid, the silver coating being considerably contracted. Not only do
baths for depositing act in this way upon a primary silver coating, but the same
results are obtained with baths for depositing other metals upon primary silver
coatings.
According to our invention we effect the deposition of other protecting coats of
metals on silver coatings with durability and permanency as follows:-that is to
say, we prevent the mutual reaction between the constituents of the secondary
bath, and the substances enclosed in the interior of the first silver coating, resulting
from the preceding process of obtaining the silver coating. And further we
prevent any ulterior inter-reaction between the said deposited diverse coatings or
impurities contained in them, and this we effect by adding to the secondary
metallic bath the remains of the silvering solution or the essential constituents of
the same, or chemically equivalent substances which produce an analogous result,
and we thus cause the reaction or decompositions, which otherwise would have
been set up in the silver coating by the secondary metal bath, or between the
diverse coatings or impurities therein, to previously take place in the said metal
bath itself.
To carry out the above described process, it is only necessary to add to the
secondary metal bath, which may be for instance a copper or a gold solution, or a
solution containing any other metal to be deposited on the silver coating, an
adequate quantity of the silvering fluid, or of its active elements, or of equivalently
acting substances, to prevent any reaction taking place between the secondary
metal bath or secondary coating and the silver coating or substances present in the
said silver coating. The proper quantities can be ascertained by a preliminary
experiment. The bath is then ready for depositing its metal on the silver
coating.
Having now particularly described and ascertained the nature of our inven-
tion and in what manner the same is to be performed, we declare that what we
claim is :-
In the manufacture of globes or shades for reflecting electric or other light, the
process of first covering a glass surface with a silver deposit, and then depositing
thereon a protecting covering of copper or other suitable metal from an electrolyte,
which has been rendered neutral or inactive by treatment with the solution from
which the silver coating was obtained, or with the substances therein contained, or
any similarly acting substances, as and for the purposes described.
Dated this 8th day of February 1897.
FELL & JAMES,
1 Queen Victoria Street, London, E.C., Agents for the Applicant.