IMPROVEMENTS IN THE MANUFACTURE OF GLASS
Year: 1838

page_text: CHANCE'S SPECIFICATION.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, ROBERT
LUCAS CHANCE, of the Glass Works, Smethwick, in the County of Stafford,
Glass Manufacturer, send greeting.
WHEREAS Her present most Excellent Majesty Queen Victoria, by Her
Letters Patent under the Great Seal of Great Britain, bearing date at
Westminster, the Nineteenth day of March, in the first year of Her reign,
did, for Herself, Her heirs and successors, give and grant unto me, the said
Robert Lucas Chance, Her especial licence, full power, sole privilege, and
authority, that I, the said Robert Lucas Chance, my exors, admors, and
assigns, or such others as I, the said Robert Lucas Chance, my exors, adñiors,
or assigns, should at any time agree with, and no others, from time to time
and at all times during the term of years therein expressed, should and
lawfully might make, use, exercise, and vend, within England, Wales, and
the Town of Berwick-upon-Tweed, the Invention of "IMPROVEMENTS IN THE
MANUFACTURE OF GLASS," communicated to me by a certain foreigner residing
abroad; in which said Letters Patent is contained a proviso, that I, the said
Robert Lucas Chance, shall cause a particular description of the nature of the
said Invention, and in what manner the same is to be performed; to be inrolled
in Her said Majesty's High Court of Chancery within six calendar months next
and immediately after the date of the said in part recited Letters Patent, as in
and by the same, reference being thereunto had, will more fully and at large
annear.

page_text: NOW KNOW YE, that in compliance with the said proviso, I, the said
Robert Lucas Chance, do hereby declare that the nature of the said Invention,
and the manner in which the same is to be performed, are particularly
described and ascertained in manner following, reference being had to the two
Sheets of Drawings hereunto annexed, that is to say :-
Whereas it is well known that in glass manufacture in the ordinary way,
and particularly in flint glass, imperfections, and in particular those thread or
fibre-like appearances in the glass called by manufacturers "stries" or strix
are visible, and the same are produced by the melted glass being allowed to
cool either preparatory to or in working the same without any artificial process
being practised to counteract the tendency of the heavier particles of the fluid
glass to subside; and whereas, although the process of stirring the fluid glass
at some period of the process of manufacturing the same has been attempted
for the purpose of remedying this defect by mingling the particles of the said
fluid into a homogeneous mass, yet the same has not been successfully practised,
partly because such process has not been carried sufficiently far, but principally
from want of some apparatus capable of withstanding the intense heat of
a glass furnace and of the melted glass, without becoming more or less
decomposed and injuring the melted glass, and at the same time adapted to
be used for manufacturing purposes:
Now, one of the said improvements in the manufacture of glass, for which
the aforesaid Letters Patent have been granted to me, consists in applying
after the completion of the process of melting the materials of which glass is
composed (whether the same be flint or crown glass), an apparatus not
hitherto used for the purpose of stirring the fluid mixture contained in the
melting pot in the manner herein-after described. I particularly apply the
said apparatus to the manufacture of glass fit for optical purposes, and the
description of the Drawing, Sheet I., hereunto annexed, and of the process of
applying the said apparatus to the furnace therein delineated, relates to the
manufacture of such glass, although, as I will hereafter explain, the said
apparatus is applicable also in the manufacture of glass intended for other
than optical purposes.
In applying it to the manufacture of glass fit for optical purposes, I have
found it requisite to use a furnace, different in some particulars of arrangement
from the ordinary glass melting furnace, although in its general construction
and operation it is not materially so. The said furnace is represented in
Figures 1, 2, and 3 of Sheet I. of the Drawings hereunto annexed.
Figure 1 is a horizontal sectional plan taken about the line 1, 2, of Figure 2;
Figure 2 is a vertical section of the furnace taken through the centre thereof;

page_text: and Figure 3 is an outside view. Instead of having a central fire-grate and
several melting pots disposed round the furnace, there is but one melting
pot a, which is placed on a large stone b, b, standing in the centre of the floor
of the furnace between the two fire-grates c, c, see Figures 1 and 2. The
object of this alteration of arrangement is to obtain a more general distribution
of heat around the pot, and there is a large hole through the stone b, b, see
Figure 2, which serves for the purpose of admitting the heat more completely
to the under side of the pot. The pot a itself is made of the same materials
as the pots in common use in glass houses, and so is the stone b. The pot a
is a plain conical vessel open at the mouth or upper part, in order that the
whole surface of the body of melted glass contained in it may be freely
accessible. d, d, are the teazing holes through which the fuel is introduced
in the usual manner, and spread over the two grates c, c.
Note. I use coke in this furnace on account of the pot a being as afore-
said entirely uncovered, for if coal were burned, the smoke and other gases
arising during the combustion of such fuel would injure the color and the
quality of the glass. e, e, e, are the flues, see Figures 1 and 2; f, f, is the
hood or chimney of the furnace.
9
The pot a is introduced into the hot furnace after having been properly
heated in a separate kiln through the opening or archway A, A, see Figures
1 and 3, and when it is so introduced the said opening is closed up by a
door (see the same Figures), in the same way that the opening through
which the pots are introduced into a common glass furnace are closed up.
There is a circular opening through the door g, see Figures 1 and 3, through
which the materials to be melted are introduced into the pot a, from time to
time during the process of melting, and that opening is closed in the intervals
in the ordinary way. i is a smaller hole in the wall of the furnace, on the
opposite side thereof to the door g, see Figure 3, for the purpose of introducing
one of the tools used in stirring the melted glass, as herein-after more par-
ticularly described. The apparatus with which the stirring is to be performed
is represented in Figure 4; it consists of a tube or cylinder with a broad
flange or rim m, the whole made of the same material as the pot a, prepared
in the same manner and with the same care.
I will now state the period of the operation of manufacturing the glass
when the said apparatus is to be used, and the manner of using the same
through the whole process of stirring. The preliminary process of melting
the materials of which the glass is to be composed in this furnace is conducted
up to a certain point in the manner practised in an ordinary glass melting
furnace, that is to say, the furnace is first heated to a high temperature, the

page_text: pot being separately heated as aforesaid. When both the furnace and the pot
have attained the proper temperature, the pot is put into its place on its stone
b, b, as shewn in Figure 2, and the opening a being closed up by its door 9,
the pot is charged with materials through the opening h by successive fillings
or partial fillings, in the manner practised in charging the pots of ordinary
glass furnace, the furnace being all the time kept up to the highest possible
temperature, as is usual, and the opening being closed between the successive
fillings until the materials in the pot a are reduced into a fluid mass properly
melted with any of the particles of saud remaining unfused. All this process
is the ordinary process of glass melting, and is conducted in the ordinary way,
subject generally to the same precautions and the same discretionary manage-
ment which are requisite in conducting the process in a furnace of the usual
construction and arrangement. When the process has proceeded as far as
above stated, the glass having arrived at that state of fusion that for the
purpose of making ordinary glass articles it would be fit to be worked, the
additional operation of stirring with the apparatus herein-before mentioned
is begun, the heat of the furnace being kept up as before. Before using the
apparatus 1, m, it must be heated in a separate furnaco up to such a tempo-
rature that it may be introduced into the furnace without being injured.
When the time comes for using the apparatus, it is introduced into the furnace
through the opening by one workman, who with a plain iron rod pushes
it into pot a, and when it is in the pot he takes hold of it with another iron
rod, not shewn in the Drawing, which has a fork formed at the end of it to
embrace the cylinder 7 under its flange m, for the purpose of guiding the
apparatus, m; at the same time another workman stands ready on the
opposite side of the furnace with one of the iron rakes n, n, shewn in Figures
5 and 6, Sheet I., which he introduces into the furnace through the opening
and as soon as the first workman has guided the apparatus l, m, across the
-melted glass contained in the pot a sufficiently near to the second workman,
the said second workman inserts the bent end of his rake h into the hollow of
the cylinder 7, and by that means forces it down into the melted glass as deep
as he thinks necessary, (taking care, however, not to plunge the rim m below
the surface of the fluid,) and then using the raken as a handle to the appa-
ratus l, m, he moves the said apparatus about in the melted glass in all
directions, so as to keep the same in motion, and thus keep all the particles
duly mixed. The heat of the furnace must be kept up all the while as high
.as possible. After the stirring has been continued some little time, the
furnace will, notwithstanding every care, be found in general to have lost
somewhat of the high temperature necessary, by the hole h having been left

page_text: open to allow the workman to move and guide the apparatus l, m, during
the stirring and previous to it; the stirring must then be stopped, the openings
h, i, closed, and the fires urged to raise the furnace again to the highest
possible heat.
After the furnace has become again sufficiently hot, the
operation of stirring the metal with the apparatus l, m, is repeated, then
stopped whenever the workman judges that the furnace has begun to cool,
and the furnace again raised to the requisite temperature, and so on. The
operation of stirring with the apparatus l, m, must be repeated at intervals,
never continuing it long enough at a time for the furnace to fall materially in
temperature until the fluid glass contained in the pot becomes a pure fluid
of uniform density, or as nearly approaching that state as the workman can
bring it; the fire grates are then stopped from beneath in the ash-pit in the
usual way of stopping the fire-grates of glass furnaces, then the furnace is
once more fired with a very full charge of fuel, and the teaze holes d aro
stopped. The workman must now begin again to stir the melted fluid in the
pot with the apparatus l, m, and must keep up the stirring without any inter-
mission whatever, except just to change the rake n which he is using for a freshi
one,
, which he will require to do frequently, as herein-after mentioned. This last
stirring is, in fact, the most important part of the stirring process, and the
more continually and regularly it can be performed the better will be the
result, for so long as the glass remains in a state of fluidity, the difference
of density of the particles of matter which compose it will cause some to
descend and others to ascend, whereby are produced the strix, streaks, or
threads which impair the homogeneity of the glass; and in order effectually
to prevent the formation of such defects, it is necessary to keep the fluid glass
in a state of motion while cooling until the process of solidification begins, or
as nearly up to that point as possible. The workman must therefore continuo
to stir the fluid glass with the apparatus l, m, while it gradually cools, and
must not stop stirring until the fluid becomes so thick as to make it actually.
too laborious and hardly practicable to stir it.
The apparatus l, m, is then carefully drawn out of the pot, in doing which
the workman who has taken the operation of stirring, pushes it over with his
rake n to the opposite side of the pot, where another workman receives it and
lifts it out of the furnace through the hole h; the furnace is then left open for
a period varying from half an hour to an hour, according to circumstances,
and after that every part of it is carefully stopped up with clay, or otherwise,
so as to exclude entirely the atmospheric air therefrom, and in that state the
furnace is allowed to cool down gradually till it is cold. The glass is then
completely made, and the pot may be removed from the furnace; it will be

page_text: found to contain a mass of glass in general free from strix or streaks either
in one large solid lump in the centre of the pot, detached from the sides
thereof, or broken into several pieces of irregular shapes, and such lumps or
pieces will be fit to be operated upon according to known processes, in order
to prepare therefrom optical glasses; the apparatus l, m, being made as aforo-
said, of the same clay as the pot a itself, is capable of being moved about, as
herein-before described, in the melted fluid in which it is partly immersed, and
exposed to all the heat of the furnace without being decomposed or affected
more than the pot itself; but as the rakes n are only protected from the
immediate contact of the melted fluid, and not from the general heat of the
furnace, they would in a very few minutes be so far decomposed by the heat
to which they are exposed as to throw off small scales, which, if they fell into
the glass, would injure the color, and produce strix or other defects; to prevent
this the workman is furnished with a sufficient supply of rakes n, to be able to
change them as often as wanted, and he must never keep one at work long
enough to allow its surface to be at all decomposed. The furnace shewn in the
Drawings is intended for the manufacture of either flint or crown glass, fit for
optical purposes; and the apparatus l, m, is also applicable in the manufacture
of both such kinds of glass, being used in the manner herein-before described.
If it is desired to apply the process of stirring to the manufacture of glass fit
for the ordinary purposes for which flint or crown glass are usually manu-
factured, a furnace of the usual construction will be employed, and the
apparatus l, m, is equally applicable for stirring the melted glass in any of
the pots at work in such furnaces, with such modifications, of course, in the
mode of introducing and moving it about, as the construction of the furnace
may render necessary. In making the stirring apparatus 1, m, of the par-
ticular form herein-before described and detached from the tools used at
intervals to move it by, the object has been to obtain an apparatus which
should be capable of being conveniently worked about in the melted fluid
contained in the melting pot, without being so affected by the heat of the
furnace and melted glass as to injure the latter, and which should at the
same time constitute a sheath or guard to the extremity of the tool introduced
into the furnace to move it by. This object is effectually answered by making
the said apparatus of the same materials as the pots used in glass melting, and
of the form shewn in the Drawings. That I do not confine myself strictly to
the use of the particular form or construction of apparatus shewn in the
Drawings, the essential and distinctive character of the apparatus l, m, con-
sisting in its being detached from the metallic rods or rakes used as handles
to move it by at intervals, so that it may remain in the furnace, although they

page_text: must be frequently changed; and in its being formed, firstly, so that it can be
freely moved about backwards and forwards through the melted fluid and
plunged more or less deep therein, in the manner herein-before described, in
order completely to stir the same; and, secondly, so that it shall act as a
sheath or guard to the ends of the rods, and as handles to move it by, to
protect them from decomposition by the heat of the melted glass, and to inter-
cept any matters which may be thrown off by their decomposition, and prevent
its falling into the glass; and with. regard to the material to be used, I must
observe also, that although I am not aware of any material so good for the
purposes herein-before described as the clay whereof glass melting pots are
made, yet I do not confine myself strictly to that particular material, but the
apparatus must be made of one of the materials known to be capable of
resisting the heat of a glass furnace without decomposition.
And another of the said improvements relates to the manufacture of sheets
of glass for windows and other purposes, when the same is conducted
according to a process known and practised in several glass manufactories in
this country, in which the glass, instead of being formed into round tables by
the common operation of flashing, is first formed into cylinders, and then
those cylinders are opened out and flattened into sheets. In the manufacture
of sheet glass as it has been hitherto practised, according to such process, the
glass when taken from the melting furnace is blown and fashioned by the
workman into a cylinder open at both ends, which is afterwards cut open down
the length of the cylinder, and then such cut cylinder is opened and flattened
into a sheet in a furnace called the flattening furnace. That furnace is divided
by a partition into two chambers, one close to and immediately heated by the
fire in which the flattening is performed, and the other more distant from
the fire into which the sheets of glass are passed to be annealed as they
are successively flattened. The flattening is performed on a stone laid on a
table extending along the furnace under the dividing partition, and a small
space is left under the said partition, through which the flattened sheet is slided
from the hot or flattening chamber on to another stone laid on the table in
the annealing chamber. In thus sliding the sheets from one stone to another
they are liable to become scratched by the hard surfaces of the stones on
which they are so slided, and any gritty or cutting matters adhering thereto.
Now, the said improvement in the manufacture of sheet. glass made
according to the aforesaid process, consists in applying to the flattening furnace
a rotatory flattening table, having one part of it in the hot or flattening
chamber of the furnace, and another part in the annealing chamber, a move-

page_text: ment of rotation being given to such table at intervals by means of suitable
machinery, in such manner that the part of the table on which the flattening
is performed is carried round with the glass upon it from the hot chamber into
the annealing chamber, and by the same movement the vacant part of the
table is brought round from the annealing chamber into the hot chamber, and
so on continuously while the operation is continued, whereby all sliding of the
sheets of glass upon other surfaces in passing them from one chamber of the
furnace to another is rendered unnecessary.
In Figures 1, 2, 3, and 4 of Sheet 2 of the Drawing hereunto annexed,
I have represented the said improvement applied to a flattening furnace.
Figure 1 is a longitudinal section of the furnace shewing the rotatory flatten-
ing table in elevation; Figure 2 is a sectional view of the furnace and table
looking from the end marked 1, 1, of Figure 1, and supposing that end wall
and the chimney removed; Figure 3 is a sectional plan; and Figure 4 is an
outside view of the furnace looking at it from the side marked 2, 2, in Figure 3.
a, a, in all the Figures represents the furnace, which does not differ in the
construction of the operating parts from a common flattening furnace, and in
the process above referred to, such slight differences as are made in it for the
purpose of adapting to it the machinery for working the rotatory table will be
apparent from the Drawing and the description herein-after contained of such
machinery. a¹ represents the hot or flattening chamber; and a², the annealing
chamber divided by the partition wall a³; C, C, is the rotatory table formed of
cast iron and mounted on an upright spindle B, which passes up through the
partition wall a³, turning in a step A at the lower end, and at the upper end
in a suitable bearing in the cast-iron cross frame D, see Figure 1 and 2. On
the spindle B is fixed a horizontal bevel wheel H, into which a vertical bevel
wheel J works mounted on a horizontal axis F, turning in bearings E and E,
see Figure 2. The rotatory motion is given to the table C, C, by turning the
axis F round by means of the wheel G, which is furnished with handles like a
steering wheel for that purpose. d is a stone laid on that part of the table C,
which is shewn in the Drawing as being in the hot chamber a¹ of the furnace,
and d' is another similar stone laid on the opposite side of the table. e is a
fixed stone table projecting into the hot chamber from the wall of the furnace,
and overhanging the table C; and e¹ is a corresponding fixed table over-
hanging the table C in the annealing chamber, see Figures 1 and 8. f is the
fire-grate; g, the fire door, see Figures 3 and 4. L is an opening into the
annealing chamber, to which. is fitted a door M, see also Figures 3 and 4;
h is an opening in the furnace wall giving access to the fixed table e, and i a

page_text: similar opening given access to the table e¹; is an opening through the end
wall of the furnace giving access to the flattening chamber at a proper height
for working the glass on the flattening table C.
Now, in working with the rotatory flattening table, the workman proceeds
as follows:-A cylinder of glass with the ends cut off and the cylinder slit
from end to end in the usual manner being brought to the opening h, see
Figure 3, he places it on the fixed table e, from whence he takes it and lays
it on the flattening stone d, where it is opened by the heat and the operations
of the workman, in the way practised in opening and flattening cylinders of
glass in the ordinary process of making sheet glass from cylinders. The
wheel G is then turned round until the rotatory table C, C, has made half a
turn, by which move the stone d and the sheet of glass just flattened on it
will be brought round from the hot chamber a¹ into the place occupied in the
Drawing Figure 3 by the vacant stone d', which will therefore now become
in its turn the flattening stone, on which the workman standing opposite the
opening will immediately begin to flatten the sheet of glass, which will have
been previously placed ready for him on the table e. The sheet first finished
will in the meantime be allowed to remain on the side of the rotatory table
in the annealing chamber until a little before the second sheet of glass is
flattened, when it will be removed by the workman (who comes for that
purpose opposite the opening i) from the flattening table to the fixed table e'.
When the second cylinder has been opened and flattened into a sheet, another
half turn will be given to the rotatory table to remove such second sheet from
the flattening chamber, and bring round the vacant flattening stone before
the flattener, and so on; the sheets of glass, as they are successively brought
into the annealing chamber, being removed from the rotatory table to the
stone e', where they are allowed to remain a little time, and then removed
therefrom by the workman who lays hold of them with a suitable tool through
the opening I, and piles them in the usual manner against the end wall of
the annealing chamber. m, m, m, see Figure 4, are the ordinary apertures
for the insertion of bars to keep the sheets separate. As to the form and
proportions of the rotatory flattening table, the same may be varied according
to convenience, and so the rotatory movement may be given to it by any
other convenient combination of wheelwork or machinery, as well as by that
which is exhibited in the Drawings, provided such an intermittent rotatory
motion be given as to produce the effect herein-before described.
Having now described the nature of the said improvements in the manu-
facture of glass, and the manner of carrying the same into effect, I do hereby

page_text: declare that, as regards the process of stirring melted glass and the furnace
berein-before described, I do not lay any claim to the same, and they have
been so described merely in order the better to explain the mode of operating
with the stirring apparatus; but I claim only the application to the process
of stirring melted glass of a detached apparatus formed in such manner and
of such material as to have the properties which I have herein-before pointed
out as the distinctive and essential properties of the apparatus l, m. And in
regard to the improvement secondly herein-before described, I claim the
application of a rotatory flattening table to the flattening furnaces used in
making sheets of glass out of cylinders, for the purpose of transferring, in the
manner herein-before described, such sheets from the flattening chamber of
the furnace to the annealing chamber, instead of sliding the sheets themselves
upon fixed surfaces.
In witness whereof, I, the said Robert Lucas Chance, have hereunto set
my hand and seal, this Eighteenth day of September, in the year of
R. L. (L.s.) CHANCE.
AND BE IT REMEMBERED, that on the Eighteenth day of September,
in the year of our Lord 1838, the aforesaid Robert Lucas Chance came
before our said Lady the Queen in Her Chancery, and acknowledged the
Specification aforesaid, and all and everything therein contained and specified,
in form above written. And also the Specification aforesaid was stamped
according to the tenor of the Statute made for that purpose.
Inrolled the Nineteenth day of September, in the year of our Lord One
thousand eight hundred and thirty-eight.
In MET