Improvements in Glazing Pottery.
Year: 1892

page_text: Date of Application, 22nd July, 1892
Complete Specification Left, 21st Apr., 1893-Accepted, 17th June, 1893
PROVISIONAL SPECIFICATION.
Improvements in Glazing Pottery.
We, HENRY LEWIS DOULTON, Potter, and ROBERT MELDRUM, Chemist,
both of The Lambeth Potteries, Albert Embankment, Lambeth, do hereby declare
the nature of this invention to be as follows:-
:-
What is known as salt glazed pottery ware has hitherto commonly been glazed
by the vapour of common salt (sodium chloride); the vapourizing being effected by
casting the salt into the kilns when they have arrived at their highest heat. The
sodium chloride is decomposed forming sodium silicate with the ware, and
hydrochloric acid, which is evolved from the shaft of the kilns.
According to this invention carbonates, hydrates and oxides of soda are
substituted either wholly or partly for the sodium chloride and by this means the
quantity of dense white vapour and noxious gases evolved is reduced to
ninimum.
a
Preferably a mixture of sodium carbonate in the form of soda ash with cominon
salt is employed the soda being in excess.
Carbonates, hydrates and oxides of potassium may also be used but these are
more costly.
Dated this 22nd day of July 1892.
H. L. DOULTON.
ROBERT MELDRUM.
COMPLETE SPECIFICATION.
Improvements in Glazing Pottery.
We, HENRY LEWIS DOULTON, Potter, and ROBERT MELDRUM, Chemist,
both of The Lambeth Potteries, Albert Embankment, Lambeth, 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 :-
What is known as salt glazed pottery ware has hitherto commonly been glazed
by the vapour of common salt (sodium chloride); the vapourizing being effected by
casting the salt into the kilns when they have arrived at their highest heat. The
sodium chloride is decomposed forming sodium silicate with the ware, and
hydrochloric acid, which is evolved from the shaft of the kilns.
According to this invention carbonates, hydrates and oxides of soda are
substituted either wholly or partly for the sodium chloride and by this means
the quantity of dense white vapour and noxious gases evolved is reduced to a
minimum.
Preferably a mixture of sodium carbonate in the form of soda ash with common
salt is employed the soda being in excess.
Carbonates, hydrates and oxides of potassium may also be used but these are
more costly.
We prefer to use a mixture of soda ash and salt in the proportion of and
respectively. By this means a cheap and convenient mixture is procured. Some-
times we use a mixture of salt and soda ash this being much cheaper than the
former.
We apply the mixture by adding it to the fire holes of the kiln when the
suitable temperature, has been attained, at intervals of 2 or 3 hours.
The
quantity we add depends on the size of the furnace, the larger the furnace the more
of the mixture is added.

page_text: When we salt kilns with a mixture of salt and soda ash we put into the fire
holes only the weight of salt which would have been used had the glazing been
done entirely by this. That is to say for every cwt. of salt previously used we now
only use cwt. of this mixture.
By adopting the above mixture we reduce the quantity of hydrochloric acid
which escapes from the chimney to a fractional quantity at least less than when
the glazing is entirely done by salt. When we use soda ash without any admixture
of salt no acid is emitted, the soda ash in this case is converted into sodium oxide
in the fire hole which is vaporised and enters into direct combination with the silica
of the ware to produce the glaze.
The chemical action which takes place is thus shown :-
Na₂O+4 (SiO2) = Na₂O (SiO2)4.
The glaze so produced by this mixture is as hard, of the same composition,
resists acids, and is in every way as stable as the ordinary salt glaze.
In using this mixture the same precautions should be taken as with ordinary salt
glazing in proportioning the quantity of mixture to be added to the kiln to produce
a satisfactory glaze.
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 :-
The employment in the glazing of pottery of carbonates, hydrates, and oxides of
sodium and potassium, substantially as described.
Dand h
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1000
H. L. DOULTON.
ROBERT MELDRUM.