IMPROVEMENTS IN THE MANUFACTURE OF GLASS MIRRORS, AND IN APPARATUS FOR GRINDING AND POLISHING PLATE GLASS, ALSO IN ENGRAVING ON GLASS
Year: 1873

page_text: LETTERS PATENT to Thomas Brown, of No. 96, Newgate Street, in
the City of London, for the Invention of "IMPROVEMENTS IN THE
MANUFACTURE OF GLASS MIRRORS, AND IN APPARATUS FOR GRINDING AND
POLISHING PLATE GLASS, ALSO IN ENGRAVING ON GLASS."-A communica-
tion from abroad. by Edouard Dodó, of Paris, in the Republic of
France.
Scaled the 2nd September 1873, and dated the 5th March 1873.
PROVISIONAL SPECIFICATION left by the said Thomas Brown at the
Office of the Commissioners of Patents, with his Petition, on the
5th March 1873.
I, THOMAS BROWN, of No. 96, Newgate Street, in the City of London,
do hereby declare the nature of the said Invention for "IMPROVEMENTS IN
THE MANUFACTURE OF GLASS MIRRORS, AND IN APPARATUS FOR GRINDING AND
POLISHING PLATE GLASS, ALSO IN ENGRAVING ON GLASS," to be as follows:-
=
In order to accelerate the operations of grinding and polishing plate
glass, and to avoid the frequent breakage of the plates which now arises,

page_text: in place of mounting the frame which carries the grinding and polishing
pads upon two cranks, one at each of its ends, I employ three cranks
at each end of the frame, the central crank at each end only being
driven whilst the cranks on either side serve only to maintain the frame
in a horizontal position and prevent it from canting.
In order also to connect the pads to the movable frame, the stem or
rod at the back of each pad is passed up through the frame, and through
washers above and below it, and a key or pin formed with a spring
tongue near to its point is passed through the upper end of the stem,
the tongue then springs outwards, and the key cannot be again with- 1
drawn without first pressing the tongue inwards.
The pad is formed of a disc of cast-iron having a hole at its centre
into which enters the stem or rod before mentioned, and the disc carries
a thick wooden block covered on its under side with felt. The pads
merely rest upon the surface of the glass to bo polished.
The glass is carried on a bed capable of being turned upon a horizontal
slide to which a to-and-fro motion is imparted. By carrying the glass
on a bed capable of turning on the reciprocating slide, the position of
the glass can readily be changed and thus the edges and centre of the
plate may without difficulty be uniformly polished. The reciprocating
to-and-fro motion is imparted to the slido by two toothed wheels carried
by two arms of a rocking lever, so that either one or other of the
toothed wheels may be caused to gear with a rack on the under side
of the slide, and the rocking motion is given to the lever by rollers in
connection with its two arms bearing against guide surfaces on the
under side of the slide.
Motion is transmitted to the driving axis of the machine by friction
cones to prevent shocks in stopping and starting the machine, and so
avoid the breakages which frequently arise when other systems of
driving are employed.
The machine above described is not only applicable for polishing glass,
but also for preparing the glass for polishing. A frame carrying bands
of cast iron is for this purpose substituted for the frame carrying the
pads. The grinding down of the surface is effected without the glass
being moved to and fro, and the rough polishing is effected as usual
with sand or grit and emery of different degrees of coarseness.

page_text: After the preliminary operations have been effected the frame carrying
the cast-iron strips is removed, and the frame carrying the pads is sub-
stituted for it and the polishing is effected without dismounting the glass
which is being operated upon.
In order to manufacture glass mirrors from rough sheet glass without
first submitting it to the operations of grinding and polishing, a platina
enamel is used of such a naturo that when spread over the surface of
a rough sheet of glass and fused in a furnace, it shall fill the hollows
on the surface of the glass and present a surface suitable for platinizing,
to obtain such an enamel the following, mixture is fused in a crucible,
1,000 grammes pure red lead, 300 grammes fused borax, 200 grammes
glass well pounded, and of the same composition as the glass to bo
coated. These three substances after being well mixed together are
placed into the crucible which has been brought to a red heat to make
sure of its being of good quality. The crucible containing the mixture
is covered over and heated in a brisk firo, 15 minutes at the most are
required to obtain a complete fusion, the crucible is then withdrawn
from the fire and the contents are poured into cold water, the product
is recovered from the water in small picces in an extremely friable
state, these are dried and afterwards pounded in a glass mortar to an
impalpable powder, to this is added 1,000 grammes essence of lavender,
and 300 grammes of platina prepared as herein-after described. Tho
mixture should be well stirred together and if too thick a small quantity
of essence of lavender may be added to it. The mixture is applied to
the glass by means of a brush and it fills up the hollows on its surface.
The sheet of glass is then dried in a drying furnace, and after being.
dried for about an hour it is heated in a similar manner as when treating
vitreous colors. The glass is then allowed to cool and the next day on
being removed from the furnace the surface of the glass coated with
enamel will have acquired a splendid' brilliancy, the roughness of tho
surface will have entirely disappeared, and the glass will have already
acquired a platina coating.
The advantage of employing a platina enamel such as above described
is that it is extremely hard and less liable to breakage than other
enamels now known.
. In order to platinize glass thus prepared I dissolvo platina in two
parts muriatic acid and one part nitric acid. The solution of platina
thus obtained is weakened down by water added to it, and the platina

page_text: is then precipitated by adding ammonia water, the precipitate is collected
on a filter paper and after being well washed is dried at a gentle heat,
afterwards the precipitate is redissolved in a small 'quantity of mixed
acid, composed half of purified muriatic acid and half of purified nitric
acid. By thus dissolving the platina a chloride solution is obtained i
with a very slight excess of acid, and this I evaporate until the whole
becomes sufficiently dry to be pulverized and then leave it to cool. I
also dissolve a quantity of pure gold in two parts purified muriatic
acid and one part purified nitric acid, and evaporate off the acid until
the chloride of gold becomes of a purple color, the solution thus
obtained is diluted down with distilled water and a quantity of sulphuric
ether is poured on to it.
The mixture is well agitated to mix the ether with the gold solution,
and is then set to rest. When the other has scized the gold and floats
upon the surface the whole is thrown into a funnel provided with a
tap. The acid being below is allowed to flow away by opening the tap,
and the tap is kept open until there remains in the funnel only ether
charged with gold. This gold liquid I mix with the platina to obtain
better reflection, opacity, and whiteness. By thus employing a com-
bination of platina and gold with borate of lead and litharge added, a
composition is obtained suitable for forming the surface of mirrors.
The borate of lead and litharge are pounded in a glass mortar and essence
of lavender is added to them, the whole is then thrown into a flask cor.
taining the platinised gold and agitated for a few minutes, and the
product is ready for use; it is applied by means of a brush, a very thin
coating is sufficient, and the glass is placed into a muffle or furnace
heated to a dull red.
For engraving the surface of glass in place of employing as heretofore
a revolving wheel or using fluoric acid I employ boracic acid. The
boracic acid is pounded in a glass vessel together with water, the
powdered product is collected and gum arabic is added to it to bring it
into a state fit for use. The mixture obtained is applied by means of
a brush or mechanical means to the surface of ground glass to produce
upon it letters, figures, and other designs as required, and is allowed to
dry, the glass is then placed into a chamber sufficiently heated to fuse
the boracic acid; wherever the composition has been applied to the
ground surface of the glass the boracic acid attacks the glass and renders
it semi-transparent.

page_text: To obtain colors of any desired shade oxide coloring matters are mixed
with the boracic acid, and to obtain a good result the oxides should
be pounded together with the acid to ensure their being thoroughly
mixed.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Thomas Brown in the Great Scal Patent Office on
the 4th September 1873.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, THOMAS
BROWN, of No. 96, Newgate Street, in the City of London, send
greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Fifth day of March, in the year
of our Lord One thousand eight hundred and seventy-three, in the
thirty-sixth year of Her reign, did, for Herself, Her heirs and successors,
give and grant unto me, the said Thomas Brown, Her special license,
that I, the said Thomas Brown, my executors, administrators, and
assigns, or such others as I, the said Thomas Brown, my exccutors,
administrators, and assigns, should at any time agree with, and no
others, from time to time and at all times then after 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
THE MANUFACTURE OF GLASS MIRRORS, AND IN APPARATUS FOR GRINDING AND
POLISHING PLATE GLASS, ALSO IN ENGRAVING ON GLASS," a communication to
me from abroad by Edouard Dodé, of Paris, in the Republic of France,
upon the condition (amongst others) that I, the said Thomas Brown, my
executors or administrators, by an instrument in writing under my, or
their, or one of their hands and seals, 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
Patent Office within six calendar months next and immediately after
the date of the said Letters Patent.
NOW KNOW YE, that I, the said Thomas Brown, do hereby declare

page_text: to be performed, to be particularly described and ascertained in and by
the following statement thereof, that is to say :-
In order to accelerate the operations of grinding and polishing plate
glass, and to avoid the frequent breakage of the plates which now arises,
in place of mounting the frame which carries the grinding and polishing
pads upon two cranks, one at each of its ends, I employ three cranks
at each end of the frame, the central crank at each end only being
driven whilst the cranks on either sido serve only to maintain the frame
in a horizontal position and prevent it from canting.
In order also to connect the pads to the movable frame the stem or 1
rod at the back of each pad is passed up through the frame and through
washers above and below it, and a key or pin formed with a spring
tongue near to its point is passed through the upper end of the stem.
The tongue then springs outwards and the key cannot be again with-
drawn without first pressing the tongue inwards.
The pad is formed of a disc of cast iron having a hole at its centre
into which enters the stem or rod before mentioned, and the disc carries
a thick wooden block covered on its under side with felt. The pads
merely rest upon the surface of the glass to be polished.
1
The glass is carried on a bed capable of being turned upon a horizontal 2
slide to which a to-and-fro motion is imparted. By carrying the glass
on a bed capable of turning on the reciprocating slide, the position of
the glass can readily be changed, and thus the edges and centre of the
plate may without difficulty be uniformly polished. The reciprocating
to-and-fro motion is imparted to the slide by two toothed wheels carried 2
by two arms of a rocking lever, so that either one or other of the
toothed wheels may be caused to gear with a rack on the under side of
the slide, and the rocking motion is given to the lever by rollers in
connection with its two arms bearing against guide surfaces on the under
side of the slido.
Motion is transmitted to the driving axis of the machine by friction
cones to prevent shocks in stopping and starting the machine, and so
avoid the breakages which frequently arise when other systems of
driving are employed.
8
The machine above described is not only applicable for polishing glass 3
but also for preparing the glass for polishing. A frame carrying bands
of cast iron is for this purpose substituted for the frame carrying the

page_text: pads. The grinding down of the surface is effected without the glass
being moved to and fro and the rough polishing is effected as usual with
sand or grit and emery of different degrees of coarseness.
After the preliminary operations have been effected the frame carrying
the cast-iron strips is removed and the frame carrying the pads is sub-
stituted for it, and the polishing is effected without dismounting the
glass which is being operated upon.
The annexed Drawing shews apparatus for grinding and polishing
glass constructed according to this Invention.
Figure 1 is a plan and Figure 2 a longitudinal and vertical section of
the machine. A is the moving frame which carries the polishing
pads a, a. It is supported at cach end by three cranks b, b³, ở³, of
which the centre one is mounted upon a revolving axis. The cranks on
either side are not driven, and serve only to keep the frame A horizontal
and prevent it canting. The pads a are attached to the frame in the
following manner :-Above and below the frame are cast-iron plates or
washers c, each with a hole in the centre for the passage of the stem d,
which is secured by a spring pin e entering the cap piece f.
The construction of the spring pin is shewn at Figure 3, and is such
that its end has to be pressed down before it can be removed. The pad
is formed of a disc of cast iron with a hole in the centre to receive the
stem d. It is furnished with a thick disc of wood covered with felt
upon its polishing face. The pad bears simply by its weight upon the
glass to be polished. The glass is bedded upon the bed stone C upon
the frame B. This frame can turn upon the carriage D, the iron ring g
which is fixed to the frame running on rollers upon the carriage. In
consequence of the mobility of the frame B the position of the glass
can be changed, and thus a uniform polish can be obtained as perfect
at the edges as in the centre and this in a much shorter time than
heretofore. The carriage D is mounted upon the rails
to-and-fro movement by means of a rack fixed upon it.
is transmitted in the following manner :-Near the middle of the
main axis F is mounted a pinion & gearing with a second pinion Z.
This pinion drives the two wheels m, m³, carried upon the rocking
frame G. These wheels may gear directly with the rack, or as the
One or
Drawings shew there may be two intermediate wheels n, n¹.
other of the wheels n, n¹, is caused to gear with the rack according
to the direction in which the carriage is required to move. То
and receives a
This movement

page_text: '
effect this I arrange upon each of the axes of the wheels, m, m², a
rod p which is forked at its lower end, and at its upper end carries a
friction wheel which runs upon the iron guide a fixed upon the carriage
(sco Figure 1, 2, and 4). This guido has an opening at the centre so
that as it moves forward one of the friction wheels reaches the break it
causes a rocking movement of the frame G, which is assisted by the
action of the counter weights r, and then the change of direction takes
place instantly the toothed wheel which was in gear leaving the rack
and the other being brought into gear with it. The main shaft F carries
at each end a bevelled wheel H, IT', gearing with the wheels K, K³,
mounted upon
the axes of the cranks which drive the frame A. A
conical friction clutch L allows the machine to be easily started and
stopped by turning the hand wheel M; this wheel is mounted on a
screw by which the concs can be forced together or separated the one
from the other. The machine above described can be employed not only
for polishing but also for the grinding and preparatory processes. It is
then only necessary to substitute for the pads a frame or slab armed
with ribs of cast iron, such as is shewn at Figuro 5. This frame or slab
should be of the same dimensions as the bed stone on which the glass is
supported, and when it is used the frame D does not receive any to-and-
fro movement. The grinding is carried on as usual with water and sand
of different degrees of fineness. When the preliminary operations are
complete the grinding frame or slab shown at Figure 5 is removed and
is replaced by the polishing pads and the polishing is effected without its
being necessary to unbed the glass. |
I
I claim as respects this part of my Invention the construction and
arrangement of machinery for grinding and polishing plate glass, sub-
stantially as described.
I also claim the method of mounting' the moving frame A upon three
cranks at either end, substantially as described.
I also claim the special construction and arrangement of the frame
carrying the glass and its carriage which permits the position of the
glass to be changed in such manner that it may le rapidly and equally
polished both in the centre and at the edges, substantially as described.
Another part of this Invention relates to the manufacture of mirrors.
In order to manufacture glass mirrors from rough plate or sheet glass
without first submitting it to the operations of grinding and polishing
I

page_text: a platina enamel is used of such a nature that when spread over the
surface of a shect of rough glass and fused in a furnace it shall fill the
hollows on the surface of the glass and present a surface suitable for
platinizing. To obtain such an enamel the following mixture is fused
in a crucible:-1,000 grammes pure red lead, 300 grammes fused borax,
200 grammes glass well pounded and of the same composition as the
glass to be coated. These three substances after being well mixed
together are placed into the crucible which has been brought to a red
heat to make sure of its being of good quality. The crucible containing
the mixture is covered over and heated in a very brisk fire. Fifteen
minutes at the most aro required to obtain a complete fusion. The
crucible is then withdrawn from the fire, and the contents are poured
into cold water. The product is recovered from the water in small
picces in an extremely friable state. These are dried and afterwards
pounded in a glass mortar to an impalpable powder, or glass crushing
rollers may also be used in this operation and the material ground with
water. The water holding the finest powder in suspension is poured off
after the grosser particles have sunk to the bottom. The fine powder is
collected and dried; to this is added 1,000 grammes essence of lavender
and 300 grammes of platina prepared as herein-after described. The
mixture should be well stirred together, and if too thick a small quantity
of essence of lavender may be added to it. The mixture is applied
to the glass by means of a brush, and it fills up the hollows on its
surface. The sheet of glass is then dried in a furnace, and after being
dried for about an hour it is heated so as to fuse the coating as when
burning in vitreous colors. The glass is then allowed to cool, and the
next day on being removed from the furnace the surface of the glass
coated with enamel will have acquired a splendid brilliancy, the rough-
ness of the surface will have entirely disappeared, and the glass will
have already acquired a platina coating.
The advantage of employing a platina enamel such as above described
is that it is extremely hard and less liable to breakage than other
enamels now known.
In order to platinize glass thus prepared I proceed as follows:-
1st Operation.-Five hundred grammes of very pure platinum is placed
in a glass flask and dissolved in one thousand grammes of muriatic acid
and one thousand grammes of nitric acid. In order to hasten the
.solution the flask is placed in a sand bath, and heated at first slightly

page_text: and then more highly. When the platinum is completely dissolved the
solution is poured into a large bowl of porcelain or glass. After cooling
5 kilos of distilled water is added to the solution. The mixture being
made, 2 kilos of liquid ammoniac is added, which as soon as it mixes
precipitates the platinum. The platinum is collected on a white paper
filter and washed with distilled water and then left to dry. When the
precipitate is thoroughly dry, 50 grammes of rectified muriatic acid and
50 grammes of rectified nitric acid is poured on to it. The whole is
then heated in the sand bath, and the solution is immediately effected.
After this solution 50 grammes of distilled water which has pre-1
viously been heated is added. The mixture is evaporated until the
chloride is dry enough to be pulverized, then the capsule is taken from
the fire and allowed to cool. By this means of operating a chlorido
of platinum is obtained almost free from acid and very easy to work.
After the cooling it is pulverized in a porcelain mortar, when it is all
thoroughly pounded, the following solution is added dron by dren and

page_text: •
poured into a glass funnel furnished with a tap, the funnel is covered
with a sheet of glass and is left to rest for 10 minutes; then the tap
is opened, and the acidulated water allowed to run out, care being taken
not to allow the auriferous liquid to pass. The flask containing, the
platinum is now placed underneath the funnel, which contains the
auriferous ether, and the tap being opened the fluid is allowed to flow
out drop by drop, the flask. should be constantly shaken. The mixturo
being made, the flask is left uncorked, and the ether is volatilized, leaving
the gold and platinum which form an intimate mixture.
.
3rd Operation.-50 grammes of litharge and 50 grammes of borate of
lead are rubbed down together with essence of lavender on a glass
palette with a muller of the same substance. 100 grammes of essence.
of lavender are used in making the mixture. When the mixture, is
thoroughly rubbed down it is put into the flask containing the auriferous
platinum, the flask is shaken for a few minutes, and its contents are
then ready for use for making reflectors. This is done by painting it on
to the surface of the glass by means of a camel hair brush; a very thin
coat is sufficient. The glass is then placed in an oven or muffle, which
is heated to a dull red. If the first coat is found to be too thin, a second
thin coat may be added without inconvenience. The application of a.
second coating is only advisable for mirrors which are worth the trouble,
such, for example, as optical reflectors and glasses.
I claim as respects this part of the Invention the method of pro-
paring the glass for mirrors without grinding and polishing by the
employment of a platinised enamel, substantially as described.
I also claim the means of producing mirrors by the use of gold and
platinum in solution, substantially as described.
For engraving the surface of glass in place, of employing, as
heretofore, a revolving wheel or using fluoric acid, boracic acid is
employed.
The process is best conducted in the following manner
1st Operation. The sheet of glass is laid upon a table covered with a
cloth, as is usual in smoothing plate glass before polishing it; then with
very fine sand the polish is removed from the sheet of glass by rubbing
it with a piece of sheet iron or zinc, changing the sand frequently. In
12 or 15 minutes the glass will be found to have completely lost its
transparency, and it is then in a fit state to be operated on by means of
boracic acid.

page_text: 2nd Operation.-2,000 grammes of boracic acid is mixed into a pasto
with water, and rubbed quite smooth with glass rubbers or mullers;
then 50 grammes of gum arabic is added, and the material is brought
to a consistency convenient for working.
3rd Operation. By means of a brush the desired pattern is produced
upon the surface of the unpolished glass by the application of the com-
position obtained by the 2nd operation. The glass is dried in the air,
and then exposed to a heat sufficient to fuse the boracic acid. The acid
then acts upon the glass at the parts where it is in contact with it,
restoring its original brilliancy, but leaving it semi-transparent. To
obtain colors of various shades it is only necessary to add coloring
oxides to the composition. The oxide should be rubbed smooth together
with the boracic acid. Colors such as yellow, green, blue, brown, red,
purple, violet, amethyst, and buff require that the glass should be sub-
mitted to a rather higher heat than is otherwise necessary, other
mixtures require very little firc.
What I claim as respects this part of the Invention is the method of
engraving glass by means of boracic acid, substantially as described.
In witness whereof, I, the said Thomas Brown, have hereunto
set my hand and seal, this Fourth day of September, in the
year of our Lord One thousand cight hundred and seventy-
three.