IMPROVEMENTS IN THE MANUFACTURE OF PLATE GLASS
Year: 1872

page_text: LETTERS PATENT to John Henry Johnson, of 47, Lincoln's Inn Fields,
in the County of Middlesex, Gentleman, for the Invention' of
"IMPROVEMENTS IN THE MANUFACTURE OF PLATE GLASS."-A com-
munication from abroad by La Société Anonyme des Manufactures
des Glaces et Produits Chimiques de St. Gobain Chauny et Cirey,
of Paris, in the Republic of France.
•11
PT
Sealed the 19th November 1872, and dated the 25th July 1872.
PROVISIONAL SPECIFICATION left by the said John Henry Johnson
at the Office of the Commissioners of Patents, with his Petition,
on the 25th July 1872.
I, JOHN HENRY JOHNSON, of 47, Lincoln's Inn Fields, in the County
of, Middlesex, Gentleman, do hereby declare the nature of the said
Invention for "IMPROVEMENTS IN THE MANUFACTURE OF PLATE GLASS," a
communication to me from abroad by La Société Anonyme des Manu-
factures des Glaces et Produits Chimiques de St. Gobain Chauny et
Cirey, of Paris, in the Republic of France, to be as follows:-
This Invention relates to the preparation or working of plate glass
by machinery, and has reference more particularly to the operation of

page_text: smoothing," which is employed for the purpose of imparting a fine
surface to the glass and rendering the same translucent after the crude
plate has been subjected to the preliminary operation of "grinding” or
"roughing down."
The operation of "smoothing" by machinery has hitherto been carried
out by the employment of metal strips or bands as a vehicle for the
emery or other rubbing powder, but their use has been attended with
many inconveniences.
Now this Invention consists in substituting for the metal strips or
bands blocks or pieces composed of any of the various species of marble
or other similar natural or artificial calcareous stone, by which increased
facility is obtained, and a considerable saving in workmanship is effected,
since the various operations may be carried on continuously by simply
changing the rubbing blocks and the powders employed to grind and
"smooth" the glass.
The blocks of marble or other calcareous stone employed may be fixed
in any suitable manner' on the frame. A simple mode of effecting
this consists in making them of the form of prismatic strips or
bands, and attaching them by means of boards screwed to the frame
to which the to-and-fro motion is imparted. This forms a species
of dovetail arrangement by which the rubbing blocks may be readily
adjusted.
It is obvious that the blocks of marble or other calcareous stone may
be employed in other operations in the preparation or working of plate
glass than that of smoothing, although they are more particularly
applicable to that purpose.

page_text: WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Twenty-fifth day of July, in the year of
our Lord One thousand eight hundreḍ and seventy-two, in the thirty-
sixth year of Her reign, did, for Herself, Her heirs and successors, give
and grant unto me, the said John Henry Johnson, Her special license
that I, the said John Henry Johnson, my executors, administrators, and
assigns, or such others as I, the said John Henry Johnson, my exe-
cutors, administrators, or assigns, should at any time agree with, and
no others, from time to time and all times thereafter 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 PLATE GLASS," a communication to me from abroad
by La Société Anonyme des Manufactures des Glaces et Produits
Chimiques de St. Gobain Chauny et Airey, of Paris, in the Republic
of France, upon the condition (amongst others) that I, the said John
Henry Johnson, by an instrument in writing under my hand and seal;
should particularly describe and ascertain the nature of the said In-
vention, 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

page_text: polishing are performed by mechanical means, the smoothing is done
by hand. The grinding and smoothing are "roughing down" operations
which most resemble each other, they only differ in the, fineness of the
bodies in powder employed to fret away the surfaces of the plate glass.
The polishing is an operation of a wholly different nature, which need
not here be taken into consideration, the improvements of which this
Invention consists being especially applicable to the operation of
smoothing.
Before entering into the details which are peculiar to the im-
provements made by this Invention in the operation of smoothing, and
the commercial results proceeding therefrom, I shall briefly describe
how the various operations herein-before referred to which constitute
the whole of the labour involved in the preparation or working of plate
glass are performed at the present time.
At the commencement of the mechanical system of working the 1
operation of grinding was performed glass upon glass by the em-
ployment in the first instance of grit or coarse sand, and successively
substituting sand of an increasing degree of fineness. The upper and
under plates of glass were thus operated upon simultaneously.
The smoothing is performed by hand, glass upon glass, different 2
"numbers" of emery powder which successively increase in fineness
being interposed. In this case also two sides are operated upon
simultaneously.
It has been since discovered that there was a great advantage in sub-
stituting for the operation of glass upon glass the employment of metals 2
as rubbing bodies, and at the present time the majority of plate glass
manufacturers have adopted this method and grind only one side at a
time.
=
The same bodies in powder, viz., grit and sand of increasing fine-
ness, are still employed, only the rubbing body no longer consists of a
a piece of plate glass of smaller dimensions, but is formed by strips or
bands of metal, cast iron, wrought iron, or steel, and occasionally even of
Bessemer metal. The form and dimensions of these metal strips or
bands vary according to the works and the mechanical means employed,
the grinding, in fact, is performed everywhere in the same manner, but 3
it is only the apparatus which differs.

page_text: One of the great problems, the solution of which has been always
sought for by plate glass manufacturers, is mechanical smoothing which
would enable machine work to be substituted for manual labour, which
daily becomes more costly.
None of the attempts hitherto made have given satisfactory results,
the mechanical means were not capable of replacing the skilled labour
which is required from the nature of the rubbing bodies employed in
the operation of smoothing, and the different speeds which are often
necessary. With the materials at present employed, if it is desired
to carry the operation of smoothing further by throwing on powders
of increasing degrees of fineness, a maximum of fineness is attained
which cannot be exceeded and which moreover produce a number of
stripes.
It will thus be seen that hitherto and in the present condition of the
operation of smoothing, mechanical means do not give any economical
advantage over manual labour. The greatest obstacle to the cm-
ployment of mechanical means in the operation of smoothing is the
nature of the rubbing materials employed, not those which like emery
and sand produce the fretting away, but those which serve somewhat
as a vehicle for the fretting substances, viz., the metal strips or bands
which have been substituted for glass. It was required to find a
material the physical constitution of which should be such that whilst
having a very homogeneous grain, no part of which was of such a nature
as to scratch the plate glass, it should at the same time possess sufficient
resistance to prevent its too rapid wear whilst serving really as a vehiclo
to the rubbing substances by admitting of their as it were fitting
therein, especially those of the grains which are too large or too hard,
and which occasion grooves or scratches of too great a depth, such
vehicle thus attenuating the roughness which naturally results from
any mechanical means. This material has been discovered by the
communicators of this Invention, and it is its application to the
operation of smoothing, and its use in the preparation or working of
plate glass, which forms the subject of this Invention.
Having been for a long time engaged in seeking the solution of a
question so important in plate glass manufacture as smoothing by
machinery, the communicators have conducted a series of experiments

page_text: all bearing upon the nature of the rubbing body. It has been
discovered that many substances, such, for example, as wood, zinc, and
artificial stone containing the substance in powder which is thrown
upon the plate glass during the operation would admit of the operation
being carried further than iron, steel, and the other hard metals. But
in these investigations the too rapid wear of the rubbing body and its
high price had also to be taken into consideration, it was also necessary
that the rubbing body should sufficiently far advance the operation
-as to render the plate glass susceptible of being at once polished.
One single nature of stone, viz., homogeneous limestone, of which
marble is the most complete type, or limestones of a similar physical
constitution, such as the stone of Soignies (Belgium), certain limestones
of Tura, lithographic stone, &c., has given such complete results as to
leave nothing to be desired. Its employment admits of the complete
application of the mechanical means already employed for the polishing
and without change of speed. Considerable facility results therefrom
in the preparaton or working of plate glass, and consequently a great
saving in hand labour, since the various operations are then performed
successively without intermission by simply changing the rubbing
blocks and the substances in powder destined to effect the fretting away
of the plate glass.
The marble blocks employed in accordance with this Invention may
be secured in various ways to the frame. A simple mode of attachment
consists in making them of the form of prismatic bands or strips, one
face of which is applied, and which are secured by means of boards
screwed to the frame to which the to-and-fro motion is imparted from
the prime mover. It is a species of handle fitted by a very simple
dovetail arrangement which admits of the ready adjustment of the
rubbing blocks.
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 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, the application
of the various species of marble or natural and artificial stones of
analogous physical constitution to the preparation or working of plate
.

page_text: glass, and more especially to the operation of smoothing whatever may
be the manner in which they are applied, or the forms or arrangements
of the apparatus employed in their application.
In witness whereof, I, the said John Henry Johnson, have to this
my Specification set my hand and seal, this Twenty-first day of
January One thousand eight hundred and seventy-three.