Improvements in the Manufacture of Reflectors.
Year: 1896

page_text: Improvements in the Manufacture of Reflectors.
We, SHERARD OSBORNE COWPER-COLES, of 39 Victoria Street, Westminster,
Engineer, and REFLECTOR SYNDICATE LIMITED, of 2 Carteret Street, Westminster,
both in the County of London do hereby declare the nature of this irvention to
be as follows:-
This invention relates to improvements in the manufacture of reflectors and
comprises the various steps hereinafter described.
According to the said invention we take a glass mould accurately shaj.ed and
polished to form a true parabolic or other reflecting surface and we deposit on
the surface of the glass a coating of silver by any known or suitable method. We
then electrically deposit upon the silver preferably after the silver has been
subjected to a burnishing process a backing of copper or other suitable common
or base metal, and during such deposit we prefer to rotate the mould in a
horizontal plane to facilitate the attainment of great regularity in the coating,
and at the same time to keep the solution in circulation. To enable the mould
to be rotated it may be conveniently supported by a ring which is suspended from
a cross bar and a swivel. The object of the swivel is to enable the silvered mould
to be passed into the backing solution,edgeways so that the copper or other metal
deposited may carry the greater part of the current. To ensure good electrical
and mechanical contact the supporting rim is accurately fitted to the edge of the
mould and after a thin film of copper has been applied to the silver a lead or
other metal ring is placed in position and in contact with the copper film. The
aforesaid ring around the edge of the mould supports the deposited metal and
ensures a clean even edge to the deposit of copper when finished. In some cases
we employ a ring of nonconducting material the result being that a thicker
deposit takes place round the periphery of the reflector thereby giving additional
stiffness. The mould with the deposited metals on it is next placed in cold or
lukewarm water and the temperature of the water is then gradually raised to
about 120° F. by which means the metals are caused to separate from the glass.
The mirror is then faced with a film of palladium or similar metal by electro
deposition.
In carrying out the above manufacture it is essential that the glass mould be
perfectly clean and free from grease before the silver is applied thereto. We
have found that if the cleaning is solely effected chemically by strong acids and
alkalies there is a great liability of causing too firm an adherence between the
silver and the glass whereby the mould is in great danger of being broken during
the removal of the coatings. We overcome this difficulty by cleaning the mould
mechanically by polishing it with a suitable polishing paste or powder and then

page_text: removing the same by washing the glass with a weak solution of ammonia prior
to the production of each mirror.
Dated this 16th day of October 1896
HASELTINE, LAKE & Co.,
45 Southampton Buildings, London, W.C., Agents for the Applicants.
Improvements in the Manufacture of Reflectors.
We, SHERARD OSBORNE COWPER-COLES, of 29 Victoria Street, Westminster,
Engineer and the REFLECTOR SYNDICATE LIMITED, of 2 Carteret Street, West-
minster, both 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 improvements in the manufacture of reflectors by a
process of electro-deposition.
According to the said invention we take a glass mould the convex side of which
is accurately shaped and polished to form a true parabolic or other reflecting
surface and we deposit on the said surface a coating of metallic silver by any
known or suitable method. We then deposit electrically upon the silver a
backing of copper or other suitable common or base metal of such a thickness as
will ensure the necessary rigidity to the finished reflector. During such deposition
we prefer to rotate the mould to facilitate the attainment of great regularity in
the thickness of the coating and at the same time to keep the solution or electro-
lyte in motion.
It is usually advisable to burnish the silver before depositing the backing
thereon. The copper or other backing adheres firmly to the silver and together
they form the reflector which is separated from the mould by placing the whole
in cold or lukewarm water and then gradually raising the temperature of the
water to about 120° F. The concave surface of the reflector thus obtained is an
exact reproduction of the convex surface of the mould and requires no further
treatment to answer all the purposes of a reflector, except that it is advisable to
coat it with a film of palladium er similar metal to prevent tarnishing of the
reflecting surface.
In order that our invention may be clearly understood we will now describe
the same with reference to the accompanying drawings in which
Figure 1 is a vertical section of the depositing tank and shows the mould
suspended therein.
Figure 2 is a section of one side of the mould and its supporting ring and of
a stopping-off ring for determining the diameter of the reflector.
Figure 3 is a similar section but taken along another diameter and shews the
mode of suspending the supporting ring of the mould.
Figure 4 is a section similar to Figure 2 and illustrates a modified form of
stopping-off ring.
Figure 5 is a similar section illustrating a modified mode of supporting the
mould.
Figure 6 is a perspective view of the cross frame for suspending the mould
and shows the metal strips for conveying the electric current from the reflector,
and
Figure 7 is a vertical section of the apparatus used for applying the protective
coating to the face of the reflector.

page_text: Like letters of reference denote corresponding parts in the several figures.
A is a glass mould accurately shaped and ground upon its convex side to a
true parabolic or other desired curve and formed with a bevelled edge a shaped
to fit accurately in the corresponding inner bevelled edge of a metal ring B
which serves to support the mould while the metal backing of the reflector is
being deposited thereon as hereinafter described. The ring B is suspended by
a vertical
bolts C from cross bars D forming a frame which is connected to
shaft E. The said shaft is carried on the main frame E of the apparatus by.a
bearing F having balls F2 which support the shaft by means of a collar E¹
thereon and allow it to rotate freely. G is a pulley through which the shaft E
and mould A may be rotated by a belt or cord G. The connection of the frame D
to the shaft E is made by a joint that allows of the mould being tilted for
the purpose hereinafter described, a locking pin e being inserted through the
joint E to keep the mould rigidly in position when not required to be tilted.
H is the depositing tank which is carried by the frame F and in which the
mould is suspended so as to be in contact with the electrolyte J which may be a
solution of any suitable salt of the metal to be deposited. K is the anode which
is arranged in the bottom of the tank H and consists of a copper plate if copper
i: being deposited so that the strength of the solution may be maintained at the
expense of the anode. K¹, K', are the conductors for conveying the current to
the anode. The electrical connection between the negative terminals and the
silver coating of the reflector, which serves as the cathode, is made through the
ring B, bolts C, strips of metal D in the arms of the frame D, the shaft E,
the bearing F,and balls F2, and a conductor L.
M is an ammeter for measuring the electric current supplied.
In carrying out the manufacture of reflectors by this process, it is essential
that the glass mould be perfectly clean and free from grease before the silver is
applied thereto. We have found however that if the cleaning is solely effected
by chemical means, as for instance by strong acids or alkalies, there is a great
liability of the silver adhering too firmly to the glass, whereby the mould is in
danger of being broken during the removal of the reflector. We overcome this
difficulty by cleaning the mould with a suitable polishing paste or powder and
then removing such paste or powder by washing the glass with a weak solution
of ammonia. This cleaning operation is repeated prior to the production of each
reflector.
After the convex side of the mould has been properly cleaned as above described,
a thin coating of metallic silver is applied thereto in any known or suitable
manner, say for example taking a solution of nitrate of silver, adding ammonia
till the precipitate at first formed is redissolved, then re-precipitating by caustic
potash and again dissolving in ammonia, and then adding glucose to the
solution and immediately dipping the mould therein, when the surface becomes
The silvered mould is then
coated with a film of silver in the ordinary manner.
placed in the ring B which latter is attached to the frame D, and serves to form
an electrical connection with the silver coating.
To determine the size of the reflector that is to be formed, and to ensure a
clean edge thereto we place around the mould a ring N (Figures 2 and 3) having
the proper internal diameter and bearing at its inner edge against the mould as
indicated in said figures. Wooden blocks N of the required thickness are
inserted between the rings B and N and the latter ring is secured in place by
clamps O as indicated in Figure 2. The ring may be made of insulating
material, or it may be a brass or copper ring having its lower face protected
by a suitable varnish to prevent the deposition of metal thereon.
During the deposition, the mould is rotated in order to ensure a uniform
thickness of deposit all over the mould and to agitate the solution J so as to
keep it thoroughly mixed and of uniform strength throughout. If desired tho
solution may be kept clean during the process by slowly drawing it off at the
bottom of the tank and gradually running fresh solution in at the top.

page_text: When first lowering the mould into the solution it is advisable to avoid
throwing the work of carrying the whole electric current upon the silver alone.
We therefore proceed as follows, that is to say we raise the shaft E by means of
pulley blocks or otherwise and suspend the mould therefrom. We then tilt the
mould and gradually lower the shaft and thereby bring the edge of the mould
in contact with the solution whereupon the circuit being established, a thin film
of copper or other base metal is deposited on the mould at the place of contact
near the edge of the mould. We then continue to lower the shaft until it rests
on the balls F2 and at the same time allow the mould to gradually assume its
horizontal position. The preceding operation occupies but a very brief interval
of time, and the current for the first few minutes is put on at its fullest pressure,
say about nine volts, to make the said current as large as possible, and to obtain
a thick preliminary coating of copper. At this stage the ring N has not been
applied and the mould simply rests in the ring B. The shaft is then rotated
and the operation of depositing the base metal, continued with a current of
moderate strength, proceeds until a sufficiently thick coating is obtained to act
as a good conductor for the electric current during subsequent deposition. The
ring B with the mould in it is then lifted out of the bath and the ring N applied
to determine the size of the reflector that is to be formed, after which the mould
is again placed in the bath and the operation of depositing the backing proceeds
until the required thickness is attained. During this stage the copper or other
metal is deposited on the mould up to the inner edge of the ring N which thus
determined the diameter of the reflector and also ensures a clean even edge to
the reflector.
In lieu of the flat ring N shewn in Figures 2 and 3 we sometimes employ for
the same purpose a leaden ring P (Figure 4) which is secured to the ring B by
the clamps O. This ring, being soft and pliable, will bend at the angle formed
by the mould and the ring B and therefore does not require to be blocked up as
does the ring N.
We sometimes employ a mould having its edges bevelled in the direction
indicated in Figure 5 that is to say in the reverse direction to that shown in
Figure 2. In such instances the mould is supported by a number of short rigid
fingers clamped to the ring by the clamps O. After the thin coating has been
applied to the mould in the manner above described the ring B with the mould
in it is removed from the bath and turned over. The fingers Q are then removed
and a ring such as P Figure 4 is applied to the mould to determine the size of
the reflector. Or instead of removing the fingers Q and applying the ring Pa
ring such as N (Figure 2) can be applied to the mould which is then replaced in
the bath and the deposition is continued as before.
After the requisite thickness of metal has been deposited, the operation is
stopped and the mould with the reflector thereon is removed from the ring B and
placed in a bath of cold or of lukewarm water which is then raised to a tempera-
ture of about 120° F. whereupon owing to the difference of expansion of the glass
mould and the metal backing the latter separates from the mould.
separation may be effected by cooling the bath instead of by heating it.
The
The concave surface of the deposited metals forms an accurate and brilliant
reflector without the necessity for any further treatment except that of coating the
For this purpose we place the reflector in a pan R Figure 7 and cover it with a
same with a thin film of ralladium or other suitable metal to prevent tarnishing.
solution of a salt of palladium for example palladium ammonium chloride. A
suitable anode S is suspended above the pan at S', this anode being curved
approximately to the shape of the reflector. T is a rod connected at one end to
the arm carrying the anode and at the other end to a pin W in a rotary disc-W
by which means the anode is caused to swing to and fro thereby agitating the
solution and preventing the deposition upon the reflector of articles of foreign
matter that may be present in the solution. The anode and the reflector are
connected respectively to the positive and negative terminal, and the back of the

page_text: reflector is preferably varnished before it is placed in the pan R to prevent local
action setting up which would interfere with the evenness of the coating.
After being coated as described the reflector has its stopped off edge removed
in any suitable manner after which it is mounted as desired.
Having now particularly described and ascertained the nature of our said
invention and in what manner the same is to be performed, we declare that what
we claim is:
1. The method of manufacturing reflectors, by depositing electrolytically a
backing of base metal upon a coating of silver applied to a anould of suitable
form substantially as described, with or without the subsequent application to
the reflector of a coating of palladium or other protective metal.
2. In the manufacture of reflectors by the above method, applying a preliminary
coating of base metal to the silver, so as to avoid said silver having to carry the
whole current, substantially as described.
3. In the manufacture of reflectors by the method referred to in Claim 1, the
determination of the diameter of the reflector by means of a stopping-off ring
substantially as described.
4. The method of separating the reflector from the mould by utilizing the
difference in their expansibility under changes of temperature, substantially as
described.
5. Our improved apparatus for manufacturing reflectors such apparatus being
constructed and operating substantially as described with reference to the
annexed drawings.
1008
HASELTINE LAKE & Co.,
45 Southampton Buildings, London, W.C., Agents for the Applicants.