Improvements in the Manufacture of Artificial Stone.
Year: 1890

page_text: Date of Application, 12th Aug., 1890
Complete Specification Left, 28th Mar., 1891-Accepted, 25th July, 1891
PROVISIONAL SPECIFICATION.
Improvements in the Manufacture of Artificial Stone.
I, CHARLES GEORGE, of 71, Belle Alliancestrasse, Berlin, in the German
Empire, Sculptor, do hereby declare the nature of this invention to be as follows :-
This invention relates to a process for the manufacture of weather-resisting
artificial stone, such as artificial sandstone, granite and marble.
In carrying out my invention, I mix the materials chosen as the basis of the
particular stone to be manufactured (which, for sandstone, consist of quartz or of
vitreous or finely-sifted common sand; and for marble or granite, of marble-dlust,
ground fluor-spar, and ground flint stone) with comparatively small quantities of
hydrate of line, blast furnace slag, silicic acid (in a gelatinous form) and hydrate of
alumina or aluminate of soda and allow the same to harden under the pressure
of steam (the presence of chloride of calcium being an advantage).
In artificial stone in which the solidification of the mass is essentially dependent
upon the absorption of carbonic acid from the air after the moulding of the mass
has been accomplished, such absorption takes place to a considerable degree; a
chemical change gradually spreading from the exterior to the interior of the stone.
If the solidification of the mass depend upon the subsequent chemical combination
of the various ingredients after the moulding of the mass has been effected, internal
chemical action and consequently molecular disturbance takes place, so that the
stone sets slowly, and, in consequence of the internal expansion caused by such
molecular disturbance, eventually contains flaws and cracks, which, though frequently
not visible to the naked eye, often give rise to the destruction of the object formed
of the stone by permitting, for example, the penetration of water; which water,
when frozen, increases the size of the crack; the crack being thus extended from
time to time until eventually a fracture occurs.
By means of the present invention, these disadvantages are avoided, because the
mass is so manufactured that only as much of the free base (lime, argillaceous earth
and sometimes sodium) is used as can be combined with the other constituent,
i.e. silicic acid, so that no considerable absorption of carbonic acid subsequently takes
place. Further, the mass is subjected to the action of steam, so that chemical
combination begins at once to take place; later injurious disturbances being
consequently avoided. A substance is thus produced which, soon after manufacture,
possesses the desired solidity.
If it be intended to manufacture, by the present process, a substitute for sandstone,
a basis is used of quartz or vitreous sand or even finely-sifted common sand, from 20
to 30 parts whereof are well mixed with about 2 to 5 parts of hydrate of lime,
1 to 3 parts of blast furnace slag to which has been added from 2 to 6% of silicic
acid (in a gelatinous form), and 1 to 3% of aluminate of soda, and also with
advantage some chloride of calcium; the whole forming a stiff paste. Such paste
is then pressed into moulds, which, when filled, are placed in a chamber containing
steam at a pressure of not less than 40 lbs., where they are left for about 6 days.
By the action of the compressed steam, the perfect chemical combination of the
lime, argillaceous earth and silicic acid, of which materials the slag used also
consists, is carried out in such a manner that a subsequent chemical combination
with large quantities of carbonic acid, which might effect a physical breaking down
of the mass, can no longer take place. In this process of combination, the chloride
of calcium has an accelerating influence, whilst the resultant soluble (chlorine or
sodaic) combinations are set free by the steam so that the manufactured mass of stone
is completely water-proof and air-tight (ie. weather-resisting), and therefore remains
free from fissures or cracks. Besides this, the steam destroys all organic germs

page_text: present in the mass, so that the growth of vegetation which would be injurious to
the stone is, as far as possible, prevented.
If a substitute for marble or granite be desired, instead of quartz, or vitreous or
common sand, the base consists of marble-dust or ground fluor-spar or flint stone or
a mixture of these. When fluor-spar alone is employed, the stone obtained is less
beautiful and less bright than if marble-dust or if a mixture of marble-dust and
fluor-spar in about equal parts be used. The 1 to 3% of aluminate of soda can be
replaced by about 3 to 5 % of hydrate of alumina.
This silicic acid for the above process can be obtained in a well-known way by
dissolving soluble sodaic glass in muriatic acid and washing out the gelatinous silicic
acid produced with water until no more muriatic acid is contained in the water
used for washing. The aluminate of soda is easily produced by fusing cryolith with
lime, and then macerating the product in water.
Dated this 12th day of August 1890.
G. G. M. HARDINGHAM,
191, Fleet Street, London, E.C., Agent for the Applicant.
COMPLETE SPECIFICATION.
Improvements in the Manufacture of Artificial Stone.
I, CHARLES GEORGE, of 12 Wartenburg Strasse Berlin, Germany, Sculptor,
do hereby declare the nature of this invention and in what manner the same is to
be performed, to be particularly described and ascertained in and by the following
statement :-
Heretofore the manufacture of artificial stones was based upon the application of
silicate of soda, which certainly produced in combination with the respective
different stone-compounds a fair material as to its strength and appearance, but is
found to be liable to cracks and finally ruptures during the course of time.
The object of my invention is to produce an artificial stone in the manufacture of
which the fundamental material is silicic acid, which is beforehand deprived of all
bases or salts, especial care being taken, that no alkaline salts remain therein, which is
done by absorbing the same by aid of lime. The silicic acid being powdered and
submitted to said treatment may be hereafter added to any of those compounds
necessary for the various imitations. Another important feature in combination
with the aforesaid process is to submit the ready moulded stone to a steam bath and
hereafter to a treatment with chloride of calcium. The product is by no means
inferior to real stone neither as to its aspect nor as to its strength, nor as to its
liability to be influenced by weather or time.
Having thus pointed out the advantages of my invention and the main points of
the process, I will now give a clear and detailed description thereof.
I grind silicic acid to powder and cleanse it from all impurities in the well known
manner. Then I mix 10 parts by weight of this powdered silicic acid with 90 parts
of water and add to this mixture 100 parts of burnt lime. I gain a silicate of
lime and I mix 100 parts of this product with 100 parts of sand and add 5 parts of
magnesia or of fluor-spar to this mixture. This mixture may be cast into moulds
so as to give various shapes as desired. The moulds then being removed, the
castings are allowed to dry as long as 12-24 hours, after which time they will be
as dry as atmospheric air. Now they are brought into a steam-boiler, and steam
blown through so as to drive out all air, after which the boiler is hermetically closed
up and steam let in under a pressure of 10 atmospheres. In this high-pressured
steam-bath the stones remain 48-72 hours and hereafter they are submitted to a
bath of boiling and saturated chloride of calcium during 6 to 12 hours, also under a
pressure of about 10 atmospheres, which may be done in the same boiler. The
condensed water may be used for the bath. The stones are allowed to dry in the
open air or, when desired to dry quickly, steam may be once more made to circulate

page_text: inside of the boiler, after the chloride of calcium has been withdrawn and before
the stones are taken out.
The stones produced in the manner heretofore described are as strong and hard
as real and natural stones and by varying the raw stone-materials, which may be
pulverized marble, magnesia, .magnesian line-stone, sand, clay and the like, any
kind of stone as marble, sand-stone, granite and so on, may be imitated to
perfection.
These stones also allow any desired colouring and polishing like common stone.
They are not liable to cracks as other artificial stones; they are perfectly fireproof
and will stand against weather like ordinary stones.
I am well aware, that steam-baths as well as baths of chloride of calcium are
made use of in the manufacture of artificial stone previous to this day, and I therefore
do not claim these processes in themselves, but what I do claim as my invention is:
1. In the manufacture of artificial stones: The method of mixing stone-material
with powdered silicic acid, being previously deprived of all free bases by treatment
with lime and by submitting the mixture, cast in moulds, to a high pressure in a
steam-boiler, exhausted of air, and hereafter to a bath of chloride of calcium, for
the purpose as described.
2. As an article of manufacture: An artificial stone in which the fundamental
material is silicic acid deprived of ali free bases and bound to lime, as set forth.
Dated. Berlin, this 18th day of July 1891.
CHARLES GEORGE.
By Robert Deissler,
38, Alexanderstrasse, Berlin, C., Germany, Agent for the Applicant.