Improved Manufacture of Artificial Granite.
Year: 1889

page_text: Date of Application, 25th Nov., 13 9-Accepted, 25th Jan. 1890
COMPLETE SPECIFICATION.
Improved Manufacture of Artificial Granite.
1, PAUL DE KRISTOFFOVITCH of No. 93 Rue Monceau Paris, France, Engineer do
hereby declare the nature of this Invention and in what manner the same is to
he performed to be particularly described and ascertained in and by the following
statement:
"
My Invention relates to an improved manufacture of the artificial granite called
Pyrogranite (for which I have obtained Letters Patent No. 14897 of 1887).
According to my improved process 1 employ a mixture of two clays having
different degress of fusibility, as before, the difference of degree of fusibility may
he as low as about 150° centigrade. The proportions of the two kinds of clay
employed may vary from one to three, to two to one of the one or the other kind,
taking into consideration their degrees of fusibility. The less fusible clay is dried
and reduced to powder or small granules; the more fusible clay is roasted and also
reduced to powder. or. small granules. . The two kinds having been intimately mixed
in the desired proportions the mixture is slightly moistened and is then subjected
to a considerable pressure in moulds of any desired form. When the blocks to be
produced require to be ornamented with mouldings or designs the mixed powders are
converted by the addition of water into a paste of the required consistency for
working it. After drying the mass, whether produced from the dry or the pasty
mixture, it is introduced into the heating furnace.
The clays emploved should have the following properties
1. A coefficient of infusibility which should not be less than 3 (Bischoff).
2. A loss under high heat which should not exceed 10 per cent. of its weight.
3. A proportion of oxide of iron below 7.75 per cent.
4. A proportion of silica which should not be below 42 per cent.
1. A coefficient of infusibility which may vary from 0.5 to 1 (Bischoff).
2. A loss under high heat which should not exceed from 7 to 8 per cent. of its
weight.
3. A proportion of oxide of iron which may reach 14 per cent.
4. A proportion of silica which may vary from 42 to 13 per cent.
The above figures need however not be strictly adhered to, as the chemical
composition of the clays varies greatly, but the proportions above given of the
mixtures should be adhered to.
The preparation of the clays in the first instance is as follows:
The less fusible clay is dried, ground and sifted, in order to obtain a uniformly
pulverulent or finely granular mass.
The more fusible clay is baked in lumps of any form, without carrying the heat to
the melting-point. This baked clay is then ground and sifted so as to reduce it to
a uniformly pulverulent or finely granular mass.
Of the clays thus prepared there are then taken by preference from 1 to 2 parts of
the less fusible clay and from 2 to 1 parts of the more fusible, and the two are
intimately mixed. A very small proportion say about 6 per cent., of water is then
dded for blocks of moderate dimensions; for blocks or slabs of large dimensions,

page_text: such as those for stair steps, paving slabs of 3 feet square &c., the quantity of water
must be greater and may amount to 20 per cent.
The moistening is effected by means of a spraying apparatus or by a steam jet
introduced among the pulverulent inixture kept in motion by an agitator in a closed
chamber. The moisting may be effected by hand but in that case it is less uniform.
When moistened, the mixture is introduced into moulds of the desired form, and
is subjected to pressure in a hydraulic or other press, such pressure being for
objects of comparatively small size and thickness, at least about 200 kilos. per square
centimetre. This pressure must be increased for objects of larger size, and in
particular of increased thickness; for very large objects it may amount to 1000 kilos.
and more per square centimetre.
For articles which, on account of their configuration, cannot be subjected to
considerable pressure, the mass is brought to a pasty condition as before described
by the addition of a larger quantity of water in order to enable it to be moulded.
When the pressing or moulding is completed the articles are dried gradually
until perfectly desiccated, and they are then introduced into the heating furnace
where the floor on which the objects are laid must be dusted over with carefully
dried granular fireclay, in order that the objects may not adhere to the floor or to
each other when subjected to the high heat, which has to be carried to the point
at which the more fusible clay melts, this temperature requiring to be maintained
for some time, taking care that during this time cold air be admitted to the furnace
fire, so as to avoid deformation of the objects. At this time the temperature will
vary between 800° and 1200° Cent. By this heating operation the following is
effected:
The less fusible clay does not change in form, the temperature being kept about
150° Cent. below that at which it melts.
The more fusible clay, on the contrary, melted and on account of its previous
intimate admixture with the refractory clay, the liquid particles thereof envelope the
granules of the latter and unite them together, forming a cohering mass, without
destroying the configuration previously imparted thereto.
By this perfect agglomeration tho objects are converted into a dense homogeneous
mass which is equal in hardness to the best granite, although it does not break with a
vitrious fracture. The cooling of the objects after this treatment should be effected as
slowly as possible in order to prevent fissuring.
If the articles are polished they assume the appearance of polished marble, the color
varying very considerably according to the nature of the clays, the proportions of the
mixture, the heat employed, and the more or less reducing action of the fire.
For obtaining the appearance of granite, the more fusible clay is only granulated
and is freed as much as possible from all powder or dust; these granules will then,
on being heated, only melt on the surface, the central part remaining solid and thus
forming in the mass paints of a different color; by varying the mixture of the clays
and the degree of fineness of the granules, a great variation in the appearance can be
obtained. The masses prepared as above described may be employed for a great
variety of purposes, such as for paving blocks or slabs, bricks, tiles, architectural or
artistic pieces, thus advantageously taking the place of articles of earthenware, stone,
marble and granite.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what 1
claim is :-
"
The improved manufacture of artificial stone or granite termed "pyrogranite"
consisting in the mixture of two clays one of which has a high melting point and is
dried and pulverised or granulated, while the other has a lower melting point and is
first baked and then pulverised or granulated, these clays being intimately mixed in
the proportions of from one to three, to two to one of either kind and after moistening

page_text: the mixture, subjecting the same to pressure in moulds, then thoroughly drying the
same and finally subjecting the mass to a temperature at which the more fusible clay
will melt either wholly or partially, whereby it is made to envelope the granules of
the less fusible clay, and a hard dense product resembling granite, or marble, is
obtained, substantially as herein described.
Dated this with ..
11000
ABEL & IMRAY,
Agents for the Applicant.