Improvements relating to Gypsum or Plaster of Paris,
Year: 1898

page_text: Date of Application, 10th May, 1890
12000
.
1000
Date of Application, 10th May, 1898
Complete Specification Left, 10th Feb., 1899-Accepted, 22nd Apr., 1899
PROVISIONAL SPECIFICATION.
Improvements relating to Gypsum or Plaster of Paris,
We, WILLIAM ROBERT JOHNSON, of 9, Dunn's Lane, Leicester, Modeller, and
GEORGE NICHOLS, 11, Prebend Street, Leicester, Plasterer, do hereby declare the
nature of this invention to be as follows:-
This invention has for its object to treat articles or goods such as moulds for
terra-cotta ware, statues, basso-relievos, mouldings and other decorations in archi-
tecture, made of gypsum or plaster of Paris in such a manner as to recover or
reclaim the gypsum or plaster of l'aris so that it can be again used for similar
purposes, while heretofore such articles, so far as they were capable of re-utiliza-
tion in the manufacture of similar articles was concerned, have been considered
as waste products.
According to this invention articles or goods made of gypsum or plaster of
Paris are first burnt to a white heat in a kiln or potter's oven.
They are then removed and while in this heated condition a solution of alum,
potash or soda or of a combination of two or more of these ingredients is thrown
over them.
When the water or most of it has evaporated in the shape of steam, the goods
are returned to the oven and when they have become sufficiently dry, they are
removed therefrom and ground to a powder in a mortar mill or other grinding
machine when the said powdered plaster of Paris can be again used in the ordinary
manner.
1000
BOULT & WADE,
Agents for the Applicants.
Improvements relating to Gypsum or Plaster of Paris.
We, WILLIAM ROBERT JOHNSON, of 4, Berridge Street, formerly of 9, Dunn's
Lane, Leicester, Modeller, and GEORGE NICHOLS, 11, Prebend Street, Leicester,
Plasterer, 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:-
This invention has for its object to treat articles or goods, such for example as
moulds for terra-cotta ware, statuettes, basso-relievos, mouldings and other
decorations in architecture, made of gypsum or plaster of Paris in such a manner
as to recover or reclaim the gypsum or plaster of Paris therefrom so that the latter
can be again used for similar purposes.
Heretofore these moulds when defective through wear or for other reasons, have
been thrown aside and new ones produced.
A principal object of this invention is to utilize the great quantity of material
locked up in these worn out' moulds and which for all practical purposes have been
considered as waste products.

page_text: To carry out this invention the aforesaid moulds or goods made of gypsum or
plaster of Paris are first burnt at a moderate temperature in a kiln, potter's oven
or other suitable place, the said moulds previous to burning being broken up into
small lumps to accelerate the burning.
The mass is then removed from the oven and allowed to become partially cool,
after which it is wetted or sprinkled with a solution of water and sulphuric acid,
about 8% or thereabouts of the latter being employed.
This should be done while the reburned plaster retains so much of its heat
derived from the reburning that a large proportion of the water is promptly
evaporated.
After the water has evaporated as described, the lumps may then be dried
either by returning them to the oven for a short time or spreading them out upon
the ground so as to allow free access of air thereto.
This acidulated plaster is then ground to a powder in a mortar mill or other
grinding machine and then if any moisture remains it may then be exposed to
moderate heat in shallow pans.
If the lumps are ground before they have become thoroughly dry there will be
a certain amount of ebullition due to the escape of the water of crystallisation
when the powder is again submitted to heat in the shallow pans and this is
allowed to continue until such escape has practically ceased.
The powder may then be allowed to cool and stored for use.
This plaster may be worked in the same manner as ordinary plaster of Paris
and is similar in its general qualities but is slower to set and harder.
It is also somewhat darker in colour but although this is an objection for some
uses it is not for moulds.
The herein before described process gives a hard, strong plaster differing only
slightly in colour from the best new plaster and under ordinary conditions at less
than half the cost of new plaster of the same quality.
Modifications may be made without departing from the principle or sacrificing
the advantages of the invention.
Instead of a solution of water and sulphuric acid (which we prefer) we may use
a corresponding solution of alum the free acid in the alum being relied upon
mainly as the useful element, or a corresponding solution of sulphate of potash.
Having now particular described and ascertained the nature of our said
invention and in what manner the same is to be performed we declare that what
we claim is:-
!
1. The process of revivifying old plaster of Paris which consists in burning,
impregnating with the substances mentioned, drying and grinding the same sub-
stantially as herein specified.
2. The process of revivifying old plaster of Paris consisting in burning same at
a moderate heat, saturating with dilute sulphuric acid, drying and grinding the
same substantially as herein specified.
3. The process of revivifying old plaster of Paris consisting in burning same
at a moderate heat, saturating with dilute sulphuric acid while a portion of the
calcining heat remains, drying and grinding and finally while in powdered state
exposing it in a thin layer to moderate heat substantially as herein specified.
Dated this Oth dov
1000
GEORGE NICHOLS,
Witness:-
E. N. LEWIS,
Berridge Street Chambers, Leicester.
Boult & Wade,
Agents for the Applicants.