Improvements in and connected with Diaphanous and Opaque Reflectors.
Year: 1899

page_text: Date of Application, 10th Jan., 1899
Complete Specification Left, 10th Oct., 1899-Accepted, 11th Nov., 1899
PROVISIONAL SPECIFICATION.
Improvements in and connected with Diaphanous and Opaque
Reflectors.
I, DOUGLAS HERMAN, of Eccleston Park, Prescot, in the County of Lancaster,
Chemist, do hereby declare the nature of this invention to be as follows:-
My present invention relates to diaphanous and opaque reflectors which aro
produced by the deposition of metallic silver upon such bases as glass, mica,
celluloid and the like, which bases are generally but not necessarily transparent.
In carrying out my invention, prepare a silver solution and a reducing
solution and mix them when required for use. The solutions may be of the
nature now generally used, but I prefer to employ special solutions, that is to
say, for the silver solution I may dissolve 4 grams of silver nitrate in the least
possible quantity of strong ammonia solution (S.G., 0.880), filter, and make up
to 1 litre with distilled water; and, for the reducing solution, I may dissolve 12
grams of Rochelle salt (sodium-potassium tartrate), in I litre of distilled water.
The glass or other base, having been made thoroughly clean, may be placed
in a shallow tray and the mixed silvering solution, heated by preference to
about 55° C., having been poured thereon until the upper surface which is to
be silvered has been covered thereby to a depth of one eighth of an inch or
more, the tray and its contents may be gently rocked, or other means may be
adopted for keeping the silvering solution in constant motion during the de-
position of the silver. It is preferred also that during the whole continuance
of the operation, the apparatus and sölution should be maintained at a tem-
perature of about 55°.
By these means a homogeneous and coherent deposit of very firmly adherent
bright silver may be obtained having as small a thickness as the one, one million
six hundred thousandth part of an inch, free from holes and forming a perfect
reflector. So thin a coherent homogeneous metallic film has not, it is believed,
even been produced hitherto by any means whatever, but it may be produced
with case and certainty in about one minute by my improved process. Deposits
five times thicker are still diaphanous, but deposits ten times thicker are prac-
tically opaque. The thinnest films on transparent bases are, by transmitted
light, of a neutral brown ("London fog") colour. As the thickness of the
deposit is increased, the colour changes to a blueish-purple which deepens with
increased thickness, until opacity is reached.
The deposition of the silver film is effected in about one sixtieth of the time
required by the shortest of the existing known processes, while the deposit is
in every respect superior.
Transparent glass silvered with a thin film as hereinbefore described, is
eminently adapted for the construction of eye-glasses, spectacles and the like
destined to diminish the glare of bright light, for lamp reflectors and generally
for similar purposes. In the case of monocles and other eye-glasses and spec-

page_text: tacles for example, the wearer may, at the same time, see by transmitted and
by reflected light, that is to say he may see objects both before and behind
him at the same time. If the silvered transparent glass be used in windows,
persons outside cannot, in daylight, see into the room through the silvered
glass whilst those inside the room can see through the window freely.
When silvering specula for telescopes and the like, by my improved process,
I prefer to employ a stronger solution and to repeat the operation two or more
times successively, taking care to arrest each step of the process before any
muddy deposit is formed. In this step by step process of building up the film
a thick strong resistant coating of silver is obtained having an extremely
brilliant surface which requires no burnishing or polishing whatever.
If it be desired to protect the deposit, this may be done by varnishing it, or
by means of a cover glass, or by both in combination. When a cover glass is
used I may employ a suitable medium between the silver film and the cover
glass thereby ensuring optical contact between the surfaces. Loss of the medium
by evaporation or leakage may be prevented by cementing together the edges
of the base and cover, or by enclosing them within a tight frame.
Improvements in and connected with Diaphanous and Opaque
Reflectors.
I, DOUGLAS HERMAN, of Eccleston Park, Prescot, in the County of Lancaster,
Chemist, 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:-
My present invention relates to diaphanous and opaque reflectors which are
produced by the deposition of metallic silver upon such bases as glass, mica,
celluloid and the like, which bases are generally but not necessarily transparent.
In carrying out my invention, I prepare a silver solution and a reducing
solution, and mix them when required for use. The solutions may be of the
nature now generally used, but I find that my best results are obtained by
employing special solutions, that is to say, for the silver solution I may dissolve
4 grammes of silver nitrate in the least possible quantity of strong ammonia
solution (S.G., 0.880), filter and make up to one litre with distilled water; and,
for the reducing solution, I may dissolve 12 grammes of Rochelle salt (sodium-
potassium tartrate), in one litre of distilled water.
The glass or other base, having been made thoroughly clean, may be placed
in a shallow tray and the mixed silvering solution, heated to about 55° C.,
or upwards, having been poured thereon until the upper surface which has
to be silvered has been covered to a depth of one eighth of an inch or
more, the tray and its contents are gently rocked, or other means are adopted
for keeping the silvering solution in constant motion relatively to the base during
the deposition of the silver thereon. During the whole continuance of the
operation the apparatus and solution are maintained at a temperature of about
65° C., but it may be observed with reference to the temperature, that a higher
or somewhat lower temperature may be employed in this and the hereinafter
described operations, but I find that the specified temperature is that which it
is more convenient to employ. If a lower temperature be maintained, the de-

page_text: posit is made at a slower rate, whilst at a higher temperature, the mixed solu-
tions become more quickly decomposed or muddy. Also, it is not necessary to
'submerge the base to be silvered, since the deposit may be produced by suitably
holding the base and pouring the solution over the surface to be silvered. Only
so much of the solutions should be mixed immediately before the operation as
will be required for the pending step.
By these means a homogeneous and coherent deposit of very firmly adherent
bright silver may be obtained having as small a thickness as the one, one
million-six-hundred-thousandth part of an inch, free from holes and forming a
perfect reflector. So thin a coherent metallic film has not, it is believed, ever
been produced hitherto by any means whatever, but it may be produced with
case and certainty in about one minute, by my improved process. Deposits
which are five times thicker are still diaphanous, but deposits ten times thicker
aro practically opaque. The thinnest films on transparent bases are, by trans-
mitted light, of a neutral brown ("London fog") colour. As the thickness of
the deposit is increased, the colour changes to a bluish purple which deepens
with increased thickness, until opacity is reached.
The deposition of the silver film is effected in about one sixtieth of the time
required by the shortest of the existing known processes, whilst the deposit is in
every respect superior.
Transparent glass silvered with a thin film as herein before described, is
eminently adapted for the construction of eye-glasses, spectacles, and the like,
destined to diminish the glare of white light, for lamp reflectors, and generally
for similar purposes. In the case of monocles and other eye-glasses and spec-
tacles for example, the wearer nay, at the same time, see by transmitted and
by reflected light; that is to say, he may see objects both before and behind
him without movement and at the same time. If the silvered transparent glass
be used in windows, persons outside cannot, in daylight, see into the room
through the silvered glass whilst those inside the room can see through the
window freely.
When silvering specula for telescopes, and generally in making the thicker
films of silver by my improved process, I may employ a stronger solution and
repeat the operation two or more times successively, taking care to arrest each
step of the process before any muddy deposit is formed. The solution may, for
example, have twice the strength of that herein before specified. In this step
by step process of building up the film, a thick, strong, resistant coating of
silver is obtained having an extremely brilliant surface which requires no bur-
nishing or polishing whatever.
If it be desired to protect the deposit, this may be done by varnishing it, or
by means of a cover glass, or by both in combination. When a cover glass is
used, I may employ a suitable medium between the silver film and the cover
glass thereby ensuring optical contact between the surfaces. Loss of the medium
by evaporation or leakage may be prevented by cementing together the edges
of the base and cover, or by enclosing them with a tight frame.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is:-
1. In diaphanous reflectors, the manufacture or production of a homogeneous
coherent deposit of bright silver so thin as to permit the transmission of light,
which cousists in treating the surface in constant motion with a heated silver
and reducing solution prepared as set forth and containing a relatively small
amount of silver, substantially as hereinbefore described.
2. The manufacture or production of opaque reflectors, which consists in treat-
ing the reflector base in constant motion with successive quantities of a heated
silver and reducing solution prepared as set forth, and in arresting each step of
the process before a muddy deposit has formed, substantially as described.

page_text: 3. The hereinbefore described manufacture or production of homogeneous
coherent bright silver reflecting surfaces, which consists in treating the surface
to be silvered with the specified heated solutions under constant relative motion,
'substantially as set forth.