Improvements in the Manufacture of Terra-cotta and like Materials, and in Apparatus therefor.
Year: 1892

page_text: Date of Application, 27th May, 1892
Complete Specification Left, 27th Feb., 1893-Accepted, 29th Apr., 1893
PROVISIONAL SPECIFICATION.
Improvements in the Manufacture of Terra-cotta and like Materials,
and in Apparatus therefor.
We, HENRY LEWIS DOULTON, Potter, and STEPHEN HENRY LEECH,
Manager, both of the Albert Embankment, Lambeth, in the County of Surrey,
do hereby declare the nature of this invention to be as follows :-
Blocks of terra-cotta and like materials warp or twist in drying and if they are
dressed to shape after drying whether before or after firing a porous surface is
formed rendering the material unfit for the exterior of buildings. The result is
that it has hitherto been impossible to produce true surfaces in terra-cotta.
According to this invention we form and thoroughly dry the blocks by any of the
methods now employed and then dress or work the surfaces to restore them to perfect
truth and correctness and we afterwards fire the same but during firing we employ
a glaze. If we use what is known as a salt glaze we find that the block is to a great
extent rendered impermeable to water without producing a polished surface so that
the block has much the same dead appearance as an ordinary unglazed block. In
cases where blocks have to fit together we erect them in the kiln or oven in the
same relative positions as they will have in the building, so that adjacent blocks
being equally affected by the fire any slight distortion which may take place during
firing will therefore also affect them equally and will be unnoticeable. In such.
cases the blocks may be caused to adhere to each other in firing by putting a thin
layer of glaze or fusible material between them.
Where extreme accuracy is required we fire the articles twice, dressing them
after the first firing and glazing them during the second, but as this is costly we
prefer to employ a special kiln which gives a very even heat. This kiln is what is
known as a box kiln. Such kilns as heretofore made have consisted internally of
an enclosed rectangular box or muffle with an arched top the ordinary arrangement
of the flues surrounding such muffle being calculated to convey the flames and
heated gases from the fires completely around the sides, bottom, and top of the
muffle, and kilns have been constructed with flues also conveying the heat over the
surface of one end, but in the usual form of box kiln one end of the muffle is entirely
occupied by the door-way, such door-way being closed whilst the kiln is heated
with either hinged or sliding iron frames carrying protective fire-clay slabs, or
brickwork temporarily built up to close the orifice. In our improved kiln the
door-way does not occupy the whole end of the muffle but only part of it and we
provide an arrangement of flues by which the greater part of the door-way end of
the muffle, is heated as well as all other sides and the top and bottom thereof.
.
Such arrangement of flues also provides for access to the interior of the muffle at
at a number of points, thus allowing of the injection of the salt at various points,
ensuring its equal distribution over the interior of the muffle.
The above described method of dressing the blocks enables us to employ for
external surfaces the perforated ends of blocks prepared in the manner described
In the Specification of the Patent granted to us on the 26th day of March 1889,
No. 5205 because after the holes have been stopped up the end can be dressed to
an even and good surface. We stop up the holes with pegs or pins of clay, con-
sisting of a preferably circular head and of such diameter as is represented by the
listance from centre to centre of the two adjacent holes-the head has a tapered
tem attached to it, its smallest diameter being immediately under the head. The
ower end of the stem is of the diameter of the hole. The head of the peg is undercut
on its underside, its edge forming an annular wedge shaped projection.
The stem of the peg is dropped into the hole until the wedge shaped projection

page_text: rests on the surface of the perforated block. Pressure now being applied to the
top of the head the wedge shaped projection is driven into the clay of the perforated
block and causes the clay between the perforations to split and contract around the
smaller diameter of the stem of the peg. As this split clay around the stem
becomes hard in drying and by burning the shank of the peg is thereby locked in
the end of the perforation and the head is securely attached to the body of the
perforated block. Or such wedge shaped projections may be dispensed with and
in place thereof pegs as before described may be used with heads flat on the under-
side, and by the action of a wedge shaped tool inserted between the heads of the
pegs the clay around the smaller diameter of the stem may be split and contracted,
attaining thereby a similar result to the wedge shape projections.
Dated this 27th day
M 1000
H. L. DOULTON.
STEPHEN HENRY LEECH.
COMPLETE SPECIFICATION.
Improvements in the Manufacture of Terra-cotta and like Materials,
and in Apparatus therefor.
We, HENRY LEWIS DOULTON, Potter, and STEPHEN HENRY LEECH, Manager,
both of the Albert Embankment, Lambeth, in the County of Surrey, 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:-
Blocks of terra-cotta and like materials warp or twist in drying and if they are
dressed to shape after drying whether before or after firing a porous surface is
formed rendering the material unfit for the exterior of buildings. The result is
that it has hitherto been impracticable to produce true surfaces in terra-cotta.
According to this invention we form and thoroughly dry the blocks by any of
the methods now employed and then dress or work the surfaces to restore then
to perfect truth and correctness and we afterwards fire the same but during firing
we employ a glaze. If we use what is known as a salt glaze we find that the
block is to a great extent rendered impermeable to water without producing a
polished surface so that the block has much the same dead appearance as an
ordinary unglazed block. In cases where blocks have to fit together we erect
them in the kiln or oven in the same relative positions as they will have in the
building, so that adjacent blocks being equally affected by the fire any slight
distortion which may take place during firing will therefore also affect them equally
and will be unnoticeable. In such cases also any desired number of blocks may be
caused to adhere to each other in firing by putting a thin layer of glaze or other
fusible material between them.
Where extreme accuracy is required we fire the articles twice, dressing them
after the first firing and glazing them during the second, but as this is costly we
prefer to employ a special kiln which gives a very even heat. This kiln is what
is known as a box kiln. Such kilns as heretofore made have consisted internally
of an enclosed rectangular box or muffle with an arched top the ordinary arrange-
ment of the flues surrounding such muffle being calculated to convey the flames
and heated gases from the fires completely around the sides, bottom, and top of the
muffle, and kilns have been constructed with flues also conveying the heat over
the surface of one end, but in the usual form of box kiln one end of the muffle is
entirely occupied by the doorway, such doorway being closed whilst the kilo is
heated with either hinged or sliding iron frames carrying protective fireclay slabs,
or brickwork temporarily built up to close the orifice. In our improved kiln the
doorway does not occupy the whole end of the muffle but only part of it and we
provide an arrangement of flues by which the greater part of the doorway end of
the muffle is heated as well as all other sides and the top and bottom thereof

page_text: Such arrangement of flues also provides for access to the interior of the muffle
at a number of points, thus allowing of the injection of the salt at various points,
ensuring its equal distribution over the interior of the muffle.
The first sheet of drawings shows a muffle made according to our invention.
Figure 1 is a front elevation the dotted lines showing a cross section.
Figure 2 is a longitudinal section.
Figure 3 is a plan in section.
The fire A is made at the back of the muffle and the gases pass up from it to a
flue B over the top of the muffle C from whence they descend partly through flués
at the sides and partly at the front through flues D D at the sides of the doorway E
and so as indicated by the arrows to the flues F at the bottom of the muffle and so
by the outlet flue to a chimney the side flues also open at the bottom into the
flues F. E is a damper for regulating the downward draft at the front and F¹ are.
dampers for regulating the draft to the side flues.
M M are passages closed by readily removeable bricks at the front of the kiln
as shown in Figure 1. They can be removed to allow of the injection of salt into
the muffle.
The above described method of dressing the blocks enables us to employ for
external surfaces the perforated ends of blocks prepared in the manner described
in the Specification of the Patent granted to us on the 26th day of March 1889
No. 5205 because after the holes have been stopped up and the heads of the pegs.
whilst still plastic have been smeared about to an approximately even surface they
can when dry be dressed to an even and good surface. We stop up the holes with
pegs or pins of clay, consisting of a preferably circular head and of such diameter.
as is represented by the distance from centre to centre of two adjacent holes-the
head has a tapered stem attached to it, its smallest diameter being immediately
under the head. The lower end of the stem is of the diameter of the hole. The
head of the peg is undercut on its underside its edge forming an annular wedge
shaped projection.
"
The stem of the peg is dropped into the hole until the wedge shaped projection.
rests on the surface of the perforated block. Pressure now being applied say by
the palm of the hand or by a "slapping board to the top of the head the wedge
shaped projection is driven into the clay of the perforated block and causes the
clay between the perforations to be pressed inwards around the smaller diameter-
of the stem of the peg. As this clay around the stem becomes hard in drying and
by burning the shank of the peg is thereby locked in the end of the perforation and
the head is securely attached to the body of the perforated block. Or such wedge.
shaped projections may be dispensed with and in place thereof pegs as before
described may be used with heads flat on the underside, and by the action of a.
wedge shaped tool inserted between the heads of the pegs the clay around the
smaller diameter of the stem may be split and contracted, attaining thereby a
similar result to the wedge shaped projections.
Sheet 2 of the drawings shows the methods of closing the ends of the holes in a
perforated block.
Figure 1 shows a section of a block with pegs of clay a b and 6-the peg a
being in position for pressure to be applied and the pegs b in position after
pressure has been applied.
The pegs have circular heads c undercut on the bottom side and tapered
stems d.
Figure 2 shows a section of a block with pegs of clay e f g h of the same
shape as a and b except that the bottom side of their heads c are not undercut.
Figure 3 is a plan of a block with 6 holes of which four have pegs inserted.
Figure 4 shows the wedge shaped tool which is inserted into the space between
the heads of the pegs.
In Figure 2 the tool has not been inserted between the pegs e and, but it has.
been inserted between the pegs f g and h.

page_text: Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed, we declare that what we
claim is :-
:-
1. The process of manufacturing terra cotta and like materials consisting in
moulding or forming the blocks, drying the same, then dressing or working their
surfaces and finally firing the same in the presence of a glaze.
2. The process of manufacturing terra cotta and like materials consisting in
moulding or forming the blocks, drying and firing the same then dressing
or working their surfaces and finally again firing the same in the presence of
a glaze.
3. The process of manufacturing terra cotta and like materials consisting in
closing the ends of the holes in a perforated block of material, drying the block,
dressing or working the surface formed by closing the ends and finally firing the
same in the presence of a glaze.
4. The methods of closing the holes in blocks of terra cotta and like material
substantially as described.
5. The kiln substantially as described and illustrated in the drawings.
Dated this 05th d...
L
1009
H. L. DOULTON.
STEPHEN HENRY LEECH.