Im-. PROVEMENTS IN THE MANUFACTURE OF LOOKING GLASSES OR MIRRORS, AND APPARATUS EMPLOYED THEREIN
Year: 1865

page_text: LETTERS PATENT to John Henry Johnson, of 47, Lincoln's Inn Fields,
in the County of Middlesex, Gentleman, for the Invention of "Im-.
PROVEMENTS IN THE MANUFACTURE OF LOOKING GLASSES OR MIRRORS, AND
APPARATUS EMPLOYED THEREIN."-A communication from abroad by the
Society Randal Cresswell, Alfred Tavernier, and Edouard Dodé, of Paris,
in the Empire of France.
Sealed the 6th June 1865, and dated the 21st March 1865.
COMPLETE SPECIFICATION filed by the said John Henry Johnson at
the Office of the Commissioners of Patents, with his Petition and Decla-
ration, on the 21st March 1865, pursuant to the 9th Section of the
Patent Law Amendment Act, 1852.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, JOHN
HENRY JOHNSON, of 47, Lincoln's Inn Fields, in the County of Middlesex,
Gentleman, send greeting.
WHEREAS I am in possession of an Invention for "IMPROVEMENTS IN
THE MANUFACTURE OF LOOKING GLASSES OR MIRRORS, AND APPARATUS EMPLOYED
THEREIN," and have petitioned Her Majesty to grant unto me, or my executors,
administrators, and assigns, Her Royal Letters Patent for the same, and
have made solemn Declaration that the said Invention is communicated to me
from abroad by the Society Randal Cresswell, Alfred Tavernier, and Edouard
Dodé, of Paris, in the Empire of France.
NOW KNOW YE, that I, the said John Henry Johnson, do hereby
declare that the following Complete Specification under my hand and seal

page_text: fully describes and ascertains the nature of the said Invention, and in
what manner the same is to be performed, in and by the following state-
ment-
This Invention relates to improvements in the manufacture of looking
glasses or mirrors whereby such articles are rendered more durable, and are
produced more economically than those inanufactured by the ordinary existing
methods, and consists of certain peculiar processes or modes of treating
platinum (which is substituted for the ordinary amalgams, or silvering),
whereby it is caused to adhere in a perfectly secure or permanent manner to
the surface of the glass employed.
In carrying out this Invention it is necessary, in the first place, to obtain
platinum in a state of minute division and suspension in a fatty body, in order
that it may be employed in metallizing the sheets or plates of glass intended
to be made into mirrors or looking glasses.
It will be readily understood that by applying the metallic coating to the
face or front surface of the glass, or to that surface upon which the reflection
is produced, all flaws or defects, such as air blows in the glass itself, will be
concealed, and that a glass of inferior color will answer fully as well as the
clearest and most brilliant plates.
In preparing the product to be applied to the glass, 100 parts by weight
of platinum, previously rolled into as thin sheets as possible or reduced to foil,
and well washed in boiling water to remove any dirt which it may have taken
up on its passage through the laminating rolls, are placed in a porcelain vessel
and dissolved in "aqua regia," composed of 400 parts by weight of pure
nitric acid and 1000 parts by weight of pure muriatic acid. In order to
expedite the dissolution of the platinum, the vessel containing the same and the
acids is placed in a sand bath, which is gradually heated to a considerable
degree of temperature. The dissolution having been accomplished, the heat
is maintained and the chloride is evaporated to dryness. At this stage of the
process the vessel is removed from the highly heated sand bath, placed in
another sand bath of a tepid heat, and there allowed. to cool gradually and com-
pletely; the product thus obtained is extracted from the vessel by means of
an ivory knife or spatula and well beaten in a glass or porcelain mortar. So
soon as it has become thoroughly reduced to a fine powder, this powder,
which should be of a good red orange color, is placed upon a glass pallet of
about 3 feet square, and upon it is poured drop by drop essence of lavender.
It is recommended that the essence of lavender be poured on to the powder
drop by drop, because if a larger quantity be poured on to the concentrated
chloride a violent explosion might occur.. On following strictly these

page_text: instructions no danger, however, will arise, although a slight effervescenco
may take place on the pallet when the essence is added; it will subside again
immediately. Care should also be taken to keep the chloride well stirred
and mixed during the addition of the essence of lavender by means of a
grinder or muller of glass. After the effervescence has subsided the grinding
and mixing operation must be continued until all the grains have completely
disappeared, which will generally require from two to three hours grinding;
the essence of lavender should be added as fast as it is taken up by the
platina. When the grinding is complete, namely, when all the grains have
been rubbed down, the mixture spread over the glass pallet is to be poured
into a porcelain vessel, and ought by this time to have taken up about 1400
parts by weight of the essence of lavender; should this amount not have been
taken up, a further quantity of the essence to complete that proportion is to be
poured into the vessel and well stirred and mixed with the rest by means of
an ivory knife; this knife may also be used in the grinding process for scraping
up or collecting together the mass on the centre of the pallet to prevent it
from running over the sides thereof. The product obtained as above
described is now allowed to stand in the porcelain vessel for about six days
in a place perfectly free from dust and damp, after which period the whole is
to be carefully filtered by passing it through filtering paper in a glass funnel.
On completing the process of filtration the salts contained in the acids that
have been evaporated will be found in the filter; these salts, by reason of the
period of repose above mentioned, will have abandoned the platinum, which
will have been taken up and held in suspension by the essence of lavender in
such minute particles that the presence of the metal will be difficult of
detection without having recourse to dessication of the product, and afterwards
melting the same. The filtered product should be again filtered in order to
be certain that none of the acids or salts have passed through the filtering
paper, and the resulting filtered product should then mark 5 degrees of the
bydrometer. The next operation is to grind upon a glass pallet by means of.
a glass muller or grinder 25 parts by weight of German litharge previously
reduced to powder in a porcelain mortar, and after this grinding 25 parts by
weight of borate of lead are to be added and well rubbed and mixed with the
litharge until the whole is perfectly smooth. Whilst effecting this grinding.
from 8 to 10 parts by weight of essence of lavender are employed, and the
product when complete is to be added to the platinum which has already been
collected in the porcelain vessel and well mixed therewith by the ivory knife.
or spatula for the space of at least one quarter of an hour, and this stirring
should also be repeated each time a portion of the mixture is taken out to be

page_text: applied to the glass. The platinum thus prepared possesses a brown color,
but when the fluxes are added thereto it loses its brown color and assumes a
grey tint. On application to the glass, which may be effected by a brusb,
the mixture presents a yellowish tint, and returns nearly to its original color,
which it retains until it is introduced into the muffle for the purpose of causing
the platinum to adhere firmly to the glass.
The firing of the glass is effected in the muffle and by the means herein-
after described. The glass to be fired is protected from contact with the
smoke, the action of which in some cases is very pernicious, and to accomplish
this object the fire-place is situate at the. back of the muffle, thereby render-
ing the charging door, which is situate in front, perfectly free from obstruction.
The shell of the improved muffle or furnace is composed of cast-iron pannels
jointed one into another, and so disposed as to admit of their number being
increased or diminished as required according to the dimensions of the plates
or sheets of glass to be fired.
Another important improvement consists in the employment of moveable
frames which are placed inside the cast-iron shell, and into which frames any
desired number of sheets or plates of glass of any desired dimensions are
introduced.
The construction and arrangement of the improved muffle and furnace will
be readily understood on referring to Figs. 1, 2, 3, 4, and 5 of the annexed
Sheet of Drawings. The muffle is composed of a number of moveable cast-
iron plates or panels A tightly jointed together, and is provided with a cast-
iron roof and floor resting on flagging c supported by arches D, beneath
which is situate the grate E, which is charged from the back by the door F.
The brick walls G, which surround and enclose the cast-iron muffle A, form
an arched roof, which is perforated with holes g, g; r, r, are pipes which
communicate between the muffle and the chamber above the perforated arch;
h,'h, are air holes aud stoppers for the purpose of cooling the muffle when
required.
The sheets or plates of glass already coated and intended to be fired are
placed vertically on one edge inside the frames H (Figs. 3, 4, and 5), pro-
vided with toothed racks I, between the teeth of which the edges of the glass
are placed, whereby a great number of sheets or plates may be fired at one
time, and sheets or plates of the largest dimensions introduced. For small
plates the frames may be subdivided horizontally by a wrought-iron plate m
fitted on catches x or on bars o held secure by hooks p. The furnace is fired
from the back and the muffle is charged from the front, and when intro-
ducing the charge the stopper s, t, is inserted to prevent the smoke rising in

page_text: the front of the muffle. P, P, are spy holes leading to the interior of the
muffle. When charging and discharging the muffle the wall Q is to be
removed and again built up as high as the top of the muffle. By this arrange-
ment of furnace the smoke and hot gases circulate round the cast-iron
muffle without being able to penetrate therein, and consequently the goods are
not liable to be injuriously affected. It is necessary to elevate the tem-
perature of the glass to a cherry red heat, in order that the fluxes of the com-
position may adhere firmly to the glass, and then to withdraw the same, but
the temperature will depend greatly on the fusibility of the glass, as of course
it must be kept below its melting point.
It will generally be found that from 4 to 8 hours duration of the firing
process will be sufficient for a muffle of medium size, according to the
charge of glass which it may contain. The sheets or plates of glass being
platinized on one side or face only, they may be secured by their uncoated face
in a single notch or tooth of the racks in the frames of the muffle, which
arrangement affords facility for firing a large number of sheets or plates of
glass at the same time.
As soon as the glass is placed in the muffle and heated it undergoes various
transformations, which I shall now proceed to describe. When the beat
begins to operate the platinum assumes a greenish color, and after passing
through several gradations of color to a brown, it finally assumes a black,
which by a sudden change becomes perfectly brilliant and lustrous, and
remains so permanently. The firing is then kept up for a few moments
longer, when the platinum disappears from view, and the glass alone is seen
of a cherry red color; the firing is then stopped, and so soon as the glass loses
its red color the brilliant and lustrous appearance of the metal again presents
itself as before. The muffle with its contents is then allowed to cool gradually,
care being taken to close up carefully the spy holes in the muffle, lest any air
entering therein should cause the fracture of the glass. Sometimes other
processes may be employed for expediting the manufacture of the product
intended for platinizing the glass; for example, in lieu of allowing the pro-
duct to stand for about six days, the product is poured into a glass funnel
provided with a stop-cock. Upon this product is poured boiling water, the
mixture being stirred at the same time with a glass stirrer and then allowed
to stand a few moments; the stop-cock is then opened, and as the essence of
lavender is of an oleaginous or fatty nature, and is contained in considerable
quantity in the mixture, it floats upon the surface of the water. The water
flows off through the opening in the cock, which must be closed so soon as the
product intended for platinizing the glass begins to escape; this operation is

page_text: repeated three or four times until the product loses its acid properties. The
hot water which flows through the open cock carries off with it in a few
minutes the salts, which would otherwise have required about six days to
become separated from the fatty or oleaginous substance which contains
the metal; this process, however, possesses one disadvantage, namely, the
waste by volatilization of the essence of lavender owing to the heat of
the water. The product which remains after the water is run off is collected
and treated in precisely the same manner as though it had been allowed to
stand for six days in accordance with the first-described process.
Another and more simple process may be adopted for removing the salts
and any remaining acid from the product, but it has a tendency to deteriorate
the quality of such product; it is, however, very expeditious, and might be
found serviceable in some cases where expedition is the chief object to be
attained. According to this process, the moment the product collected from
the pallet is placed in the porcelain vessel, in place of allowing it to stand for
six days and awaiting the deposition of the salts, 12 parts by weight of dis-
tilled water are poured over it, and the vessel is placed on a moderately heated
sand bath and the product is heated until a light vapour is evolved therefrom,
and until the water which has been poured in rises in small bubbles to the
surface of the product. This heating process is continued for some minutes;
the product is stirred with an ivory spotula in order to mix the water with
the product, the vessel is removed from the sand bath and allowed to cool,
and the product is slowly poured into a paper filter, care being taken to avoid
the pouring in of the water which will be found at the bottom of the vessel.
The effect of this process is, that the small amount of hot water having been
well mixed with the product which contains the metal and the salts will be
taken up by the latter and will leave the metal to the essence of lavender,
which causes this last process to be less profitable than that wherein the
product is allowed to repose for six days, for in compelling the salts to pre-
cipitately leave the platinum, they carry off with them in the form of chloride
a certain portion of the metal, and consequently a product less rich and there-
fore more costly is obtained; for in order to recover the platinum which will
be combined with the salts, it is necessary to treat them by the usual methods
for that purpose, and hence there are two processes involved in lieu of one.
In the processes above described the proportions may be varied, but the results
will not be so satisfactory, and will be more uncertain.
Having now described and particularly ascertained the nature of the said
Invention, and the manner in which the same is or may be used or carried into
effect, I would observe in conclusion that I lay no claim to the application

page_text: of platinum to glass for the purpose of producing looking glasses or mirrors,
neither do I-claim the use of essence of lavender or of litharge in the prepa-
ration of the metallizing product; but what I consider to be novel and
original, and therefore claim as the Invention secured to me by the herein-
before in part recited Letters Patent, is,―
First, the peculiar processes or modes of preparing a product to be employed
in metallizing glass with a view to the manufacture or production of looking
glasses, mirrors, and other reflecting surfaces, as herein-before described.
Second, the peculiar processes for extracting or removing the salts and acids
from the metallizing product, as herein-before described.
Third, the peculiar construction and arrangement of closed muffle and
furnace for firing the glass after it has been coated with the metallizing
product, as herein-before described and illustrated by the Drawings.
Fourth, the application and use of moveable frames provided with toothed
racks for containing or holding the sheets or plates of glass when inside the
muffle, as herein-before described.
In witness whereof, I, the said John Henry Johnson, have hereunto
set my hand and seal, this Eighteenth day of March, One thousand
eight hundred and sixty-five.
J. HENRY JOHNSON. (L.B.)