Improvements in and connected with the Glazing of Bricks and like Articles.
Year: 1893

page_text: Date of Application, 10th May, 1893
Complete Specification Left, 5th Feb., 1894-Accepted, 17th Mar., 1894
PROVISIONAL SPECIFICATION.
Improvements in and connected with the Glazing of Bricks and
like Articles.
I, WILLIAM CROOKES, of 7 Kensington Park Gardens, in the County of
Middlesex, Fellow of the Royal Society, &c. do hereby declare the nature of this
invention to be as follows:-
The glazed bricks and tiles of commerce as now manufactured are comparatively
expensive and they are usually made of fire-clay although several attempts have
been made to glaze the ordinary building brick and tile. I have discovered that this
result may be satisfactorily accomplished if the glazing material is correctly
proportioned with relation to the component parts of the brick or tile. I find by
experiment that a satisfactory glaze may be made composed of red lead, silica,
kaolin, carbonate of soda, carbonate of potash, nitrate of potash, oxide of tin,
arsenic, and usually to these ingredients should be added a proportion of chloride
of sodium. The proportions of the ingredients will vary with the constituents
from which the brick or tile is made, and my experiments have been carried out
with bricks composed of ordinary brick earth, common clay, London clay, sand
and chalk in varying proportions such as are commonly used for indoor and also
for outdoor work; and I find that the glaze may also be produced on certain other
classes of clay when mixed with Derbyshire lime-stone. An excess of chalk in
the mixture makes a very porous brick, while where the brick contains an excess
of clay the fusing point is lowered, but the bricks are apt to twist and warp when
firing unless great care is taken. When using lime-stone instead of chalk it should
be thoroughly pulverized and carefully mixed in a creamy state; the result being
an extremely hard brick resembling grey stone. Generally speaking the bricks to
be treated or glazed should not be sanded but should be left with the natural surface
which should be as smooth as possible. If after the brick has been pressed it is
gone over with a wet cloth or brush to "wash up," an artificial surface as is some-
times done I find that the brick is liable to scale when the surface is enamelled and
consequently a brick produced by direct pressure or machine pressed is preferable
where a glazing or enamelling is to be satisfactorily produced and the drying
should be slow and the bricks biscuit-baked in the kiln at a uniform heat. In
regard to the enamelling; the ingredients used should be thoroughly mixed and
reduced to an almost impalpable powder and should be fused as promptly after
compounding as possible as some of the materials are liable to absorb water. The
material should be fused preferably in fire-clay pots covered during the fusing
period. The resulting enamel should be perfectly white and opaque. After fusing,
the enamel may be cast on an iron or other slab in cakes and when it is desired to
use the same it should be reduced to a very fine powder by grinding between hard
stones, care being taken not to allow any iron to get in. The powder so produced
is mixed with water until it has about the consistency of cream and the face of the
bricks is then dipped therein or they may be coated by passing them on an endless
band under a vessel from which the "cream " is allowed to run. If to the water
used in making the above a small quantity of gelatine is added, say about two
ounces for each gallon of mixture the coated bricks after drying and before firing
can be handled without any fear of disturbing the surface. The gelatine will buru
out in the firing without causing any stain. Such firing should be continued until
the surface is perfectly bright and glossy as anything less than this will produce a
dull surface on the finished brick. The atmosphere surrounding the bricks during

page_text: the glazing should be slightly oxidizing rather than reducing. A little extra heat
will do little or no damage to the enamel. The process of cooling should be very
slow or there is danger of crazing. By varying the proportions of the various
materials the enamel may be adapted for bricks or tiles of varying compositions.
Speaking generally the effect of increasing the quantity of soda or potash is to
lower the fusing point; but the resulting glaze is not so satisfactory and is liable
to craze when exposed to the weather. An increase in the proportion of silica will
on the contrary raise the fusing point but will reduce the opacity of the glaze and
produce a pearly look which is sometimes desirable on very hard brick. An
increase in nitrate of potash will give a fine white tint, but if added in excess will
cause crazing, in the same way that the carbonate does; while an excess of red
lead will lower the fusing point but the glaze loses opacity. The oxide of tin has
great power over the glaze and an increase in the proportion of this material lowers
the fusing point and produces a fine milky white glaze, but if too much be added
craże will make its appearance; as will, also an excess of arsenic which will also
completely alter the glaze and destroy its colour. Kaolin in excess will give a
dead opaque surface with loss of gloss, as will also any great excess of chloride of
sodium.
Dated the 10th dow of Mo 1802
PHILIP M. JUSTICE,
55 & 56, Chancery Lane, London, Chartered Patent Agent,
For the Applicant.
COMPLETE SPECIFICATION.
Improvements in and connected with the Glazing of Bricks and
like Articles.
I, WILLIAM CROOKES of 7 Kensington Park Gardens, in the County of
Middlesex, Fellow of the Royal Society &c. 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 :-
The glazed bricks and tiles of commerce as now manufactured are comparatively
expensive and they are usually made of fire clay although several attempts have
been made to glaze the ordinary building brick and tile. I have discovered that
this result may be satisfactorily accomplished if the glazing material is correctly
proportioned with relation to the component parts of the brick or tile. I find by
experiment that a satisfactory glaze may be made composed of red lead, silica,
kaolin, carbonate of soda, carbonate of potash nitrate of potash, oxide of tin,
arsenic, and usually to these ingredients should be added a proportion of chloride
of sodium. The proportions of the ingredients will vary with the constituents
from which the brick or tile is made, and my experiments have been carried out
with bricks composed of ordinary brick earth, common clay, London clay, sand
and chalk, in varying proportions, such as are commonly used for indoor and also
for outdoor work, and I find that the glaze may also be produced on certain other
classes of clay when mixed with Derbyshire or like limestone. An excess of chalk
in the mixture makes a very porous brick, while where the brick contains an excess
of clay the fusing point is lowered, but the bricks are apt to twist and warp when
firing unless great care is taken. When using limestone instead of chalk it should
le thoroughly pulverized and carefully mixed in a creamy state; the result being
an extremely hard brick resembling grey stone. Generally speaking the bricks to
be heated or glazed should not be sanded but should be left with the natural surface
which should be as smooth as possible. If after the brick has been pressed it is
gone over with a wet cloth, a brush or trowel, to "wash up an artificial surface,
as is sometimes done, I find that the brick is liable to scale when the surface is
"

page_text: After
enamelled, and consequently a brick produced by direct pressure or machine
pressed is preferable where a glazing or enamelling is to be satisfactorily produced
and the drying should be slow and the bricks biscuit baked in the kiln at a uniform
heat. In regard to the enamelling, the ingredients used should be thoroughly mixed
and reduced to an almost impalpable powder and should be fused as promptly after
compounding as possible, as some of the materials are liable to absorb water. The
material should be fused preferably in fire-clay receptacles covered during the
fusing period. The resulting enamel should be perfectly white and opaque.
fusing, the enamel may be cast on an iron or other slab in cakes, or while fully
fused poured directly into water, and when it is desired to use the same it should be
reduced to a very fine powder by grinding between hard stones, care being taken
not to allow any iron or other metal to get in. The powder so produced is mixed
with water until it has about the consistency of cream, and the face of the bricks
is then dipped therein or brushed over with the enamel, or they may be coated by
passing them on an endless band under a vessel from which the " cream is allowed
If to the water used in making the above a small quantity of gelatine,
size or the like is added, say about two ounces for each gallon of mixture, the
coated bricks after drying and before firing can be handled without any fear of
disturbing the surface. The gelatine or size will burn out in the firing without
causing any stain. Such firing should be continued until the surface is perfectly
bright and glossy, as anything less than this will produce a dull surface on the
finished brick. The atmosphere surrounding the bricks during the glazing should
be slightly oxidizing rather than reduoing. A little extra heat will do little or no
damage to the enamel. The process of cooling should not be too rapid or there is
danger of crazing. By varying the proportions of the various materials the
enamel may be adapted for bricks or tiles of varying compositions.
to run.
33
Speaking generally the effect of increasing the quantity of soda or potash is to
lower the fusing point, but the resulting glaze is not so satisfactory and is liable to
craze when exposed to the weather. An increase in the proportion of silica will
on the contrary raise the fusing point but will reduce the opacity of the glaze and
produce a pearly look which is sometimes very desirable on very hard brick. An
increase in nitrate of potash will give a fine white tint, but if added in excess will
cause crazing in the same way that the carbonate does, while an excess of red lead
will lower the fusing point but the glaze loses opacity. The oxide of tin has
great power oven the glaze and an increase in the proportion of this material
lowers the fusing point and produces a fiue milky white glaze, but if too much be
added craze will make its appearance. An excess of arsenic will also completely
alter the glaze and destroy its color. Kaolin in excess will give a dead opaque
surface with loss of gloss, as will also any great excess of chloride of sodium.
My experiments have been carried on mainly with bricks of the following
character and composed of the following materials.

page_text: The enamels I have prepared of the following materials and proportions by
weight:
ENAMEL No. 1.
Red lead 30 parts, silica 30 parts, kaolin 14 parts, carbonate of soda 5 parts,
carbonate of potash 4 parts, nitrate of potash 2 parts, tin oxide 2 parts, arsenic
2.7 parts, sodium chloride 1.8 parts.
ENAMEL No. 2.
Red lead 30 parts, silica 30 parts, kaolin 14 parts, carbonate of soda 5 parts,
carbonate of potash 4 parts nitrate of potash 2 parts, tin oxide 6 parts, arsenic
2.7 parts, sodium chloride 1-8 parts.
Red lead 30 parts, silica 30 parts, kaolin 14 parts, carbonate of soda 5 parts,
carbonate of potash 4 parts nitrate of potash 2 parts, tin oxide 2 parts,
arsenic 2-7 parts.
ENAMEL No. 5.
Red lead 30 parts, silica 30 parts, kaolin 14 parts, carbonate of soda 5 parts,
carbonate of potash 4 parts nitrate of potash 2 parts, tin oxide 2 parts, arsenic
3 parts, sodium chloride 1-8 parts.
The above ingredients being thoroughly mixed and reduced to such a fine state
of division that they would pass through a comparatively fine sieve (say 40 mesh)
were fused at a white heat until all the materials were in combination, after which
the enamel was poured on to a cold polished iron slab so as to form small cakes or
sheets.
In regard to the enamels so produced I found No. 1 was very suitable for
enamelling bricks Nos. 1 and 2. No. 2 formed a very fine white glaze suitable
for bricks No. 3, as did also enamel No. 3, which however produced a pearly white
glaze. No. 4 produced a white glaze suitable for bricks containing more clay than
bricks No. 3, while enamel 5 produced a good creamy white glaze suitable for
bricks No. 2, and my experiments lead me to believe that a slight variation in the
proportions of the tin oxide, arsenic, and sodium chloride, and occasionally of the
other materials will enable a suitable enamel to be prepared for bricks of various
characters.
I do not of course confine myself to the exact proportions stated for I have
explained that these may be varied within certain limits, and the effect of certain
variations while it is of course evident that the enamel must be prepared to suit
the particular brick or other article it is intended to treat, the object being to
produce a glaze which shall have practically the same coefficient of expansion and
contraction with heat and cold as will the particular class of brick or other article
to be coated.
I am aware that it has heretofore been proposed to produce for ordinary bricks
an enamel composed of oxide of tin, silica, carbonate of soda, nitre or sea salt, red
lead and borax in varying proportions, and also to substitute felspar or fluorspar
for the silica in such mixture, and I do not broadly claim the use of these materials
or any of them.

page_text: Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare. that what I
claim is :-
.1. The enamels or glaze for bricks or like articles prepared substantially as
herein before set forth.
2. The improvements in glazing or enamelling bricks or like articles, consisting
in first mixing the ingredients, then fusing same, cooling and comminuting the
enamel so produced, mixing with water and applying same with or without a
proportion of gelatine, size or the like, substantially as set forth.
3. In the glazing of bricks or like articles the admixture with the enamel of
gelatine, size or the like for the purpose described.
Dated the 2nd day of Febuary 1894.
PHILIP M. JUSTICE,
55 & 56 Chancery Lane, London, Chartered Patent Agent,
For the Applicant.