An Improvement in or pertaining to the "Salt-glazing” of Earthenware, Stoneware, and other Fictile Articles.
Year: 1895

page_text: Date of Application, 18th Jan., 1≥95
Complete Specification Left, 18th Oct., 1895-Accepted, 23rd Nov., 1895
PROVISIONAL SPECIFICATION.
An Improvement in or pertaining to the "Salt-glazing” of
Earthenware, Stoneware, and other Fictile Articles.
I WALTER SMITH of 9 Albert Hill Terrace Bishop Auckland in the County of
Durham Gentleman do hereby declare the nature of this invention to be as
follows:-
•
The object of my invention is to provide that earthenware stoneware and other
fictile articles can and shall be glazed by salt (commonly called "salt-glazing") in
a more complete effective and efficient manner than is ordinarily the case.
To carry out this object I use the trioxide of chromium commonly known as
chromic acid in the following manner.
According to one method of use a solution of chromic acid is mixed with and
kneaded into the dry clay dust until the requisite paste or tempered clay has been
produced wherefrom the required articles are made and salted and burnt and
otherwise treated as is customary and necessary and the consequence of the intro-
duction of the solution of chromic acid will be that the articles will have taken the
"salt-glaze" more efficiently and will produce the desired results more effectively
than would otherwise have been the case.
According to another method of use a bath of a solution of chromic acid is
prepared and when the articles have been moulded or otherwise made into shape
and are sufficiently dry being in the condition called the "white-hand" or there-
abouts and before they are burnt they may be dipped or plunged into this bath so
often as may be desired or may be retained therein so long as may be necessary
and can then proceed to undergo the remaining ordinary stages of the treatment
when again the "salt-glazing "has been more efficiently and effectively performed.
Again instead of immersing these articles in the bath as aforesaid their surfaces
may be washed or brushed or otherwise treated with this solution whereby the same
effect will be produced.
According to another method of use the articles may be immersed in the bath or
the surfaces thereof may be treated with the solution as aforesaid after the ordinary
first burning and when they are in the condition called the "biscuit" and can then
proceed to undergo the remaining ordinary stages of the treatment when again the
salt-glazing "has been more efficiently and effectively performed.
66
It is perhaps as a general rule preferable to use chromic acid alone without any
admixture but when it may for any reason be desirable so to do any compound or
salt that has chromic acid as a base may also be used amongst which I may instance
bichromate of potash and bichromate of soda.
When substances or compounds are to be used which are not soluble in water oil
or any other suitable liquid may be employed instead.
In some cases say for example when chromate of lead is to be used it may be
rubbed on the surface of the "biscuited" article in a dry state.
In some cases again particular and special results are desired when the "salt-
glazing" is completed and whenever this is so as also on all other occasions when
desired any suitable material or materials that will produce these results or that
TD071

page_text: may be advisable for any cause may be added to and used with the chromic acid in
such proportions as may be convenient.
Dated this 18th day of January 1805
HART & Co.,
186, Fleet Street, London, E.C., Agents.
An Improvement in or pertaining to the "Salt-glazing” of
Earthenware, Stoneware, and other Fictile Articles.
I, WALTER SMITH of 9 Albert Hill Terrace Bishop Auckland in the County of
Durham Gentleman 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 object of this my invention is to provide that earthenware stoneware and
other fictile articles can and shall be glazed by salt (commonly called "salt-
glazing") in a more effective and complete economical and efficient manner than is
ordinarily the case.
To carry out this object I use chromic acid or that is to say as a general rule the
trioxide of chromium in manner as is hereinafter described.
According to one method of use a solution of chromic acid is made of a strength
of 1 lb. avoirdupois of chromic acid dissolved in five gallons of water or thereabouts
and this solution is absorbed by and mixed with and kneaded into such a quantity of
dry clay dust as will produce a paste or tempered clay of the requisite consistence
or plasticity wherefrom the required articles can be made in any customary or
other manner.
The quantity of the dry clay dust that will so absorb this solution
of chromic acid will vary with the quality of the clay and the fineness to which it
is ground but as a general rule I consider that five gallons of the solution mixed
with 1 cwt. avoirdupois of dry clay dust will produce a paste or tempered clay that
will be suitable for the manufacture of most articles.
A modification of this method of use consists in producing a paste or tempered
clay from and by very finely ground or almost impalpable dust of a suitable clay
mixed with the solution of chromic acid in manner as is herein before described but
of a somewhat thinner consistence or more in a semi-liquid condition and in the
state commonly known as "dip" or "slip" and when the clay article has been
moulded or otherwise made into the required shape in any customary or other
manner it is dipped into this "dip" or "slip" in the usual way and a certain
quantity thereof will adhere to such clay article and form a coating thereover and
will create a smooth surface thereon by which modification a certain economy in the
use of the chronic acid solution will obviously be effected.
According to another method of use a bath of a similar solution of chromic acid
is made of about the same strength as is hereinbefore described and when the clay
article has been moulded or otherwise made into the required shape in any
customary or other manner and is sufficiently dry being in the condition called the
"white hand" it is dipped or plunged into this bath and instantly withdrawn there-
from and as a general rule I consider that one such dipping will be found sufficient
although more than one dipping may be given when desired.
A modification of this method of use consists in washing or brushing or otherwise
applying this solution of chromic acid hereinbefore described to and on the surface
of the clay article when in the "white hand" condition by a brush or other suitable
appliance and as a general rule I consider that in this modification also one such
coat will be found sufficient although more than one coat may be applied when
desired.

page_text: In this method of use the solution of chromic acid may be made stronger wheu
desired by dissolving say four lbs. or six lbs. or even more of the chromic acid in
the five gallons of water it being understood and remembered that the greater the
proportion of chromic acid in the solution the darker and richer will be the colour
of and generally the more efficient thick and possibly brilliant will be the glaze on
the article when completed.
According to another method of use a similar bath of a similar solution of
chromic acid is made as is herein before described and when the clay article has
been moulded or otherwise made into the required shape in any customary or other
manner and having been treated as is usual has undergone the ordinary first
burning being in the condition called the "biscuit" it is dipped or immersed in this
bath in which condition it may although it need not necessarily be instantly with-
drawn therefrom or it may remain immersed in the solution so long as may in each
case be desired or it may be dipped and withdrawn and then allowed partially to
dry when it may be dipped again and so on as often as may in each case be
desired.
A modification of this method of use consists in washing or brushing or otherwise
applying this solution of chromic acid herein before described to and on the surface
of the clay article when in the "biscuit" condition by a brush or other suitable
appliance and as a general rule I consider that in this modification one such coat
will be found sufficient although more than one coat may be applied when desired.
In this method of use also the solution of chromic acid may be made stronger
when desired in manner as is hereinbefore described it being similarly understood
and remembered that the stronger the solution and the louger the article remains
immersed or the oftener it is dipped therein (of course up to the point of saturation)
or the more coats that are applied the darker and richer will be the colour of and
generally the more efficient thick and possibly brilliant will be the glaze on the
article when completed.
The effect and consequences of this use of chromic acid hereiubefore described
may be deemed to be and may be described as being the following.
When the clay article has been produced and made by or has been treated
in and according to one of the methods of use herein before described the solution
of chromic acid will have been absorbed or partly absorbed by the clay and will
have entirely permeated therethrough or will have penetrated thereinto with great
rapidity and on the article being subjected to heat in the usual manner in the
ordinary course of manufacture the oxygen in the chromic acid will be rapidly
given off at a low temperature and the chromium alone in infinitesimally small
particles remains and under the conditions described in the first beforementioned
method of use pervading the whole mass of the clay or of the clay coating or
under the conditions described in the other beforementioned methods of use on
the surface of this article and also penetrating to a certain depth below such
surface and thus a kind of coating or shield or suchlike protection is afforded to
and provided for the clay of which such article is made. When therefore this
article is salted in the usual manner in the ordinary course of manufacture the
fumes of the sodium are not as is ordinarily the case at the present time for
two or three saltings absorbed by the porous and "thirsty" clay but contrariwise
these fumes commence at once to act on and perform their desired function on
the surface of the clay and thus as is indeed obvious a thicker and possibly a more
brilliant glaze is obtained in perhaps even less than the given time usually allowed
for the complete series of saltings in a more economical and efficient manner as is
desired.
It is therefore evident that chromic acid alone is necessary for and needful in
performing this my invention but as is well known chromic acid is somewhat
noxious and harmful even if not dangerous in using and certainly requires very
careful handling as also elaborate appliances and precautions for its safe keeping in
a proper condition for use and for these reasons amongst others it may frequently
be desirable and advantageous although not obligatory to use instead thereof some

page_text: compound or salt that has chromic acid as its base or as one of its constituents and
this can duly and properly be done in the same manner as is herein before described.
It is obvious however that the greater the proportion of chromic acid that is
contained in any particular compound or salt the more useful and suitable in many
respects is such particular compound or salt as for example in respect of the
quantities thereof that must be used to produce the required solution of the desired
strength herein before described and therefore I would especially mention bichro-
mate of potash and bichromate of soda as being amongst others extremely suitable
as well as convenient for use although I would have it clearly understood that I do
by no means limit myself thereto.
I may further state that I consider that the best results are as a general rule
obtained when water is used as the solvent and especially of the compound that has
chromic acid as its base or as one of its constituents but some of such compounds
that it may in some particular cases or occasionally be desired to use may not be
soluble in water and then and in these cases oil or other suitable liquid may be
employed for this purpose instead of water and in the same manner oil or other
suitable liquid may be employed when the particular compound that it is desired to
use is not soluble therein but is only miscible therewith.
On some occasions and when some clays are used as also whenever it may be
desired so to do it may be advisable or expedient for the purpose more especially of
ensuring and enhancing the brilliancy and lustre of the glaze on the article when
completed as also for other purposes of convenience efficiency and the like to add
to the solution of chromic acid hereinbefore described a certain quantity of hypo-
sulphite of soda either in the form of a solution or otherwise as may be desired.
The hypo-sulphite of soda must not be added in such quantity as to overpower the
chromic acid and as a general rule I consider that the proportions thereof should
not exceed three parts of hypo-sulphite of soda to one part of chromic acid by
weight and also that even this proportion of hypo-sulphite of soda can oftentimes
be advantageously reduced.
66
In some cases again particular and special results may be desired when the
'salt-glazing" is completed and whenever this is so as also on all other occasions
when it may be desired so to do any appropriate and suitable material or materials
that will produce these results or that for any other cause may be advisable can be
added to and used with the chromic acid in such proportions and under such forms
and after such a manner as may be convenient or desirable or expedient or
necessary in each particular case.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is
In and for or pertaining to the "salt-glazing" of earthenware stoneware and
other fictile articles the use of chromic acid substantially as and for the purposes
herein before described and declared.
Dated this 18th day of October 1805
HART & Co.,
168, late 186, Fleet Street, London, E.C., Agents.