Improved Process for Producing Ceramic Masses.
Year: 1897

page_text: Date of Application, 19th Feb., 1897-Accepted, 8th May, 1897
Improved Process for Producing Ceramic Masses.
We CHARLES COWEN SCHIRM Landscape Painter and OTTO LESSING
Proffessor, both of No. 51 Königin Augusta Strasse Berlin Germany do hereby
declare the nature of our invention and in what manner the same is to be
performed to be particularly described and ascertained in and by the following
statement:—
The ceramic masses hitherto known are not advantageous for producing finely
perforated, delicate wares, such as figures & groups of figures and isolated
ornaments, because they shrink when drying and particularly whilst being fired
and are liable to break in consequence of the excessive contraction. In treating
these masses in moulds; the greatest care is necessary and the moulds must be very
plain, otherwise the mass, which is very brittle when dried, will easily crumble.
It has hitherto been quite impossible to cast the mass, as may be done with
plaster of Paris, a process which is very advantageous, owing to the artistic
freedom it gives, and to the great facilities it offers in manufacturing.
The present invention obviates the first mentioned disadvantages & attains the
advantages of the above mentioned process.
About 6 parts of finely ground porcelain, earthen or similar well fired mass are
mixed with one part of barnt plaster of Paris and one part of a suitable flux, the
quality of which must be determined by the temperature at which the mass is to
be subsequently fired. The result is worked up after the manner of plaster of
Paris and may then be cast in moulds in the same way as this plaster.
This composition hardens, like plaster of Paris to a perfectly hard mass, which
may be easily worked, does not contract whilst drying nor shrink when fired to any
noticeable extent. It forms a hard porcelain-like body when fired, and at a much
lower temperature than is the case with clay, earthenware or porcelain.
These properties of the composition are easily explained, the amount of gypsum
employed is quite sufficient to bind the mass, and it combines with the flux when
the mass is fired. The main body of the composition consists of materials, which
have been already fired and consequently do not shrink on being again fired, and
are evenly and firmly cemented together by the comparatively small amount of
flux employed.
If for instance the flux consists of glaze which melts, say at 1000° Centigrade,
which is strong enough for all ordinary purposes, a perfectly durable, hard material
will be attained at this temperature.
The fact that the mass may be cast in moulds in the same manner as plaster of
Paris enables the same free working of the mass and in consequence the same
artistic freedom in the application of the same as is the case with plaster of Paris,
its application being just as simple and cheap. In some cases, when it is not
required to fire the mass very sharply it is advantageous to treat the same with
waterglass or other silicate solution, in that the object in question is allowed to
remain in the solution from two to eight days.
This latter step should not be mistaken for the known process of saturating the
wares with waterglass by coating the same therewith. In this latter case the
waterglass is decomposed by the carbonic acid of the air, carbonate of soda or
potassium being formed and silicic acid being freed. The carbonate of soda, which
is formed in considerable quantities if the coating is repeated often, gives rise to

page_text: salty excretions, and sweating, which is very disadvantageous under certain
circumstances.
According to the present process, if perfectly anhydrous plaster of Paris has
been employed, silicate of lime and sulphate of soda or potassium will be formed
after the firing has taken place, owing to the prolonged immersion in the
waterglass solution. The silicate of lime will be deposited in the pores in the
from of an impervious mass, rendering the composition harder and more compact,
whilst the sulphate of soda or potassium, will remain in the solution.
After having
been washed, for a short time in clear water, the mass will only contain fired or
burnt materials having their pores filled up with silicate of lime and containing no
substances capable of sweating out subsequently.
The process, once much resorted to, of saturing plaster of Paris with waterglass,
is quite different in its effects to the above described method.
Cast or set plaster of Paris, which retains the water added to harden it, in the
form of crystall water, does not decompose, when saturated with or dipped in
waterglass solutions, a thin superficial coating of silicate of lime is formed, which
excretes considerable quantities of the so called hair-salt. The plaster. of Paris
remains undecomposed in the interior of the mass; a silicifying of the whole mass
does not take place.
$
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, we declare, that what we
claim, is :-
1. An improvement in the production of ceramic masses which consists in
employing fired materials only (porcelain, earthenware etc.) and in adding plaster
of Paris and a flux thereto in about the proportion of six parts of burnt or fired
materials to one part of plaster of Paris and one part of flux in the manner and for
the purpose substantially as described.
2. The process which consists in mixing fired, powdered materials, plaster of
Paris and flux as specified, firing the mixture thus produced and saturating it
subsequently in a waterglass solution substantially as described.
Dated this 19th day of February 1897.
BOULT & WADE,
Agents for the Applicants.