IMPROVEMENTS IN THE MANUFACTURE OF POTTERY
Year: 1884

page_text: We HERBERT MINTON ROBINSON of Stoke upon Trent, Manufacturer, and
MINTONS Limited of Stoke on Trent China, Earthenware and Tile Manufacturers
and LEON ARNOUX of Stoke upon Trent Art Director of the Company do hereby
declare the nature of the invention for IMPROVEMENTS IN THE MANUFACTURE OF
POTTERY to be as follows:-
The use of compressed air applied to articles in the clay state formed either in
the inside or on the outside of moulds for the purpose of giving them a closer
texture and reducing their contraction.
The compressed air is produced by an air pump, single or double action, stored
in a receiver and connected by small pipes with either the mould or, in the case of
flat or small pieces, with a chamber containing several moulds, which is hermetically
closed. The pressure applied is indicated by a manometer communicating with
the inside of the mould or chamber,
The practical use of the invention is apparent from the fact that the majority of
defects in production of pottery or porcelain are caused by the excessive shrinkage
they undergo in drying and firing on account of the open texture and the unequal
pressure given by the potter to different parts of the same piece.
The application of compressed air equally over the surface of the piece will
produce a denser texture and consequently obviate many of the losses in
manufacturing,
This process has never before been adopted in England.

page_text: Improvements in the Manufacture of Pottery.
We HERBERT MINTON ROBINSON, Manufacturer of Stoke upon Trent and
MINTONS Limited of Stoke upon Trent China Earthenware & Tile Manufacturers
and LEON ARNOUX Art Director to Mintons Limited, Stoke upon Trent do hereby
declare the nature of our invention for IMPROVEMENTS IN THE MANUFACTURE OF
POTTERY and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement :-
.
The object of this invention is to equalise the pressure on the manufactured
pieces, reduce their shrinkage and obtain a better and neater impression from the
moulds by the employment of compressed air either applied inside or outside the.
mould.
Pottery is made either by pressing the plastic clay by hand on the plaster mould,
or by casting it inside the mould with clay in a liquid state. By the first process
it is difficult to give by hand an equal amount of pressure to every part of the
piece, by the second, a considerable shrinkage takes place when drying and firing,
attended by great risks, in both cases malformation, cracks, breakages and other
-defects are the consequence.
In using compressed air which acts in all directions & equally and simultaneously.
on every part of the piece and by the facility it gives of obtaining a much
greater amount of pressure than was possible by hand work, the invention
diminishes or does away with the majority of these defects-Also in the case of a
cast piece the admission of compressed air into the interior expels the moisture
contained in the clay adhering to the mould more rapidly and prevents those parts
from falling away which without support are apt to come down by their own
weight.
In the case of those pieces which have to be cast the mechanical appliances are,
an air pump (A), with single or double action, worked by machinery a metal
receiver (B) to store the compressed air, with a safety valve (C) to regulate the
amount of pressure and a manometer (D) shewing the pressure per square inch.
A tank (E), for the slop clay, with a cover hermetically fitting on the top.
Three india-rubber pipes (H) rather large, from the bottom of the clay tank to
the bottom of the plaster mould, another pipe (G) from the receiver to the cover of
the clay tank and (F) from the receiver to to the centre of the metal cover of the
mould. A platform (I) on which the mould (K) stands, with two pillars supporting
the metal cover, allowing it to be adjusted to the proper height.
The mode of procedure is as follows, the tank filled with slip (liquid clay), of a
proper consistency, is well stirred, to expel any air bubbles it may contain, the
cover is then screwed on and compressed air is admitted and the slip rises by the
pipe (H) and is allowed to flow in the trough (L) as long as any air bubbles come
to the surface, the waste slip is carried from the trough to a bucket outside by the
pipe (M) When the operator is satisfied that there are no more bubbles, the
running of the slip is stopped and the plaster mould (K) is placed on the platform

page_text: so that the pipe from the clay tank enters underneath in the centre, all the pipes
are then closed except the tap (N) which allows the compressed air to act on the
surface of the slip, which under the pressure rises steadily in the mould, this
tap (N) in the hand of the operator gives him the most perfect control over the
admission of the slip.
When the deposit of clay against the plaster mould is of the required thickness
the tap (N) is closed and the tap (0) on the cover of the tank is opened to allow
the compressed air to escape, and the slip falls back into the tank by gravitation,
leaving the inside of the cast piece free from any superfluous slip, the communi-
cation between the mould and the clay tank is then closed, the metal cover is
lowered on to the top of the mould and screwed tightly down, the amount of
pressure is regulated by the weight on the safety valve, and then by opening the
tap (P) the compressed air is admitted from the receiver into the mould by the
pipe (F) fitting in the centre of the mould cover, The length of time that the
compressed air is allowed to act inside the piece depends on its size and thickness-
When this is done the cover is raised and the process is complete, the consistency
of the deposit against the mould being found much denser and harder than would
have been the case if cast in the ordinary way, the heat generated by the
compression of the air assisting in the hardening of the clay.
The application of compressed air to the pieces pressed in plastic clay is shewn
in the drawing by the two diagrams (Q) and (R), in the first the mould is shewn
upside down and compressed air is introduced by opening the tap (S), in the second,
the mould stands upright and the air is introduced by the tap (T) The moulds
stand on india-rubber rings and are made air tight by a metallic cover fitting on
the top and forced downwards by a lever provided with an eccentric.
Respecting the pieces made from clay bats the process is shewn by the figure (V)
in which a clay bat (U) of proper hardness is squeezed between two metal
forms (X & Y) The former producing the inside face of the piece and the latter
the under part. When the clay bat has been placed between the two brass moulds,
the horizontal piece (Z) under which the upper mould is screwed is firmly fixed
and the compressed air admitted into the compartment (a) underneath-By the
action of the compressed air the lower brass mould rises and the bat is squeezed
against the horizontal piece (Z)-The leather diaphragm (b) allows this motion
upwards of the lower brass frame without any air escaping-as soon as the piece
is squeezed the horizontal piece is unfastened and the small channel (c) connecting
the compressed chamber with the under part of the clay piece is opened to allow
the compressed air to act on the back of the same and lift it up from the mould.
Having now particularly 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 use, for pottery purposes, of compressed air acting on the inside of a clay
piece cast or pressed in the inside of a plaster mould, for squeezing, supporting and
hardening the said piece in the manner shewn in the annexed plan, as a novel
feature in the manufacture of Pottery.
2. The action of compressed air on the surface of liquid clay in a tank placed on
a lower level than the mould, in such a manner that the clay may be raised to any
height in the mould or in the building, & supply one or several moulds, allowing
the superfluous slip to fall back into the tank without manipulation and to be used
over again, by opening the small tap on the cover of the tank & allowing the
compressed air to escape as shewn in the drawing.
3. The compressing and moulding of flat pieces made from clay bats purposely
prepared-These being placed between two metal forms are squeezed by the rising
of the lower form acting against a horizontal piece fastened across the top, to which
the upper form is screwed, the lower mould or form being fixed on the cover of the
compressed air chamber-which rises by the expansion of the compressed air

page_text: i
admitted This upward motion is facilitated by the leather diaphragm fixed round
it, making at the same time this compartment air tight as shewn in the plan.
4. The use of compressed air for lifting the finished piece from the mould by
'opening the small channel & establishing a communication between the compressed
air chamber and the bottom part of the piece in the manner shewn in the plan.
Dad thin ih da 100k
H. M. ROBINSON.
L. ARNOUX.
Pp. Mintons Limited,
H. M. ROBINSON, Secretary.