Improvements in the Manufacture of Enamelled Goods.
Year: 1893

page_text: Date of Application, 2nd Nov., 1893-Accepted, 2nd Dec., 1893
COMPLETE SPECIFICATION.
Improvements in the Manufacture of Enamelled Goods.
I, HUBERT CLAUS, of Thale of Hartz in the Empire of Germany, Engineer,
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:-
My invention relates to improvements in the manufacture of enamelled goods by
which goods made of sheet-steel or sheet-iron are effectually enamelled by means
of a single thin cover of enamel, which has a very pleasing appearance.
In the methods heretofore in use for producing articles with a single cover of
enamel, an enamel was employed which caused oxidation of the metallic surface.
This was due to the fact that the parts of the enamel, consisting of silicate, borax,
gypsum, soda, and the like were compounded in such a manner that they completely
vitrified, and that all ingredients which could prevent oxidation were expelled from
the enamel. The acid contained in the enamel thus becoming liberated, caused the
oxidation of the metallic surface while the enamel was drying. The composition
of the ingredients of the enamel necessary for this purpose requires the reduction
of the alkaline compounds of the enamel, for the formation of free acids to produce
the oxidation.
.
The character of the oxidation which is to produce spots in the enamel, therefore
depends on the alkaline components of the enamel. The increase of alkaline
component parts reduces the oxidation and likewise the complete vitrification
hence the enamel is not so transparent and the spots formed are not so clearly
seen.
It is well known that the reduction of the alkalies and increase of the flux in
enamel has the effect of lowering the fusing point and of rendering it less capable
of resisting chemical agencies.
Enamel having the composition above referred to, after being applied to the
article, requires a careful supervision during the drying-process, in order to obtain
the desired surface-oxidation. The drying-process therefore, is of considerable
importance. This process takes place in a stove or closed room, the temperature
of which depends upon the degree of dampness of the external atmosphere. In
order therefore, to obtain any desired degree of oxidation, the necessary temperature
must be determined and frequently changed, with changing external conditions, and
in doing this, many of the articles are improperly treated and are spoiled, and must
be submitted anew to the process of re-covering with enamel and of re-drying.
The oxidation, or spotting of the enamel in the operations above described still
however follows the structure of the metal, marking by stronger or feebler oxida-
tion, or spotting, the smoother parts and recesses of the surface, because within the
recesses, on account of the intensified action of the free acids in presence of air and
water, a stronger oxidation takes place, than is the case on the plain and smooth
parts.
Articles made of rough and soft iron of fibrous structure are therefore best suited
for the process of oxidation as above described, whereas oxidation, that is to say
the formation of rust, does not take place so readily on hard, homogeneous metals,
such as steel or sheet-iron, which, on account of their homogeneity do not show the
variety of spotting which is desirable.
The present invention, which consists in the manufacture of a new sort of enamel
for the purpose in question, and in a new process of oxidation, for producing spots
in the enamel, obviates all the objectionable features above indicated, viz.: the
employment of a glassy brittle enamel, the great care required in drying in a
separate heated drying-room, and the dependence on the structure of the metal.
Price 8d l

page_text: The ingredients of the enamel are compounded without regard to the possibility
of effecting the oxidation of the enamel by means of free acids, the enamel itself
being of an alkaline nature.
It is known that the addition of alkali, especially of felspar, considerably
augments the refractory properties of the enamel, and at the same time increases
the power of the enamel to resist chemical agencies, and also facilitates the
covering power and close union of the enamel with the iron through formation of
ferrous silicate.
I will now give by way of example the proportions of the ingredients of the
enamel, premising that the same may within certain limits, be altered without
changing the nature of the invention. These proportions are as follows:
130 parts felspar, 125 parts borax, 70 parts quartz,
25 parts soda, 17 parts saltpetre, 10 parts fluor-spar,
4 parts antimony, 0.5 parts cobalt.
These ingredients are thoroughly mixed and melted, and ground with water with
the addition of fuller's earth, until the enamel can be spread out in a thin, uniform,
coherent layer.
The articles to be treated, after being previously scoured and washed in the well-
known manner, are covered with the enamel, prepared as above indicated, and are
then powdered with a mixture of equal parts of blue vitriol and green vitriol,
then dried in the usual manner in the atmosphere, and when air-dry, they are
burnt or fired.
During the powdering with the salts indicated russet and blackish spots are
formed on the surface, which give to the enamel covering an alternate dark and
light colour and a spotted appearance.
The spotting of the enamel through alternation of dark and light spots can be
varied by using powdered salts of different degrees of fineness, for instance: if
suitably sized grains of the mixture are chosen, and if the greyish-white and dark
spots are suitably arranged, the appearance of the surface of a fracture of coarse-
grained granite may be imitated on the surface of the enamel.
What takes place here is somewhat as follows: At those places where the salt
particles drop on to the wet enamel, a coagulation of the enamel, during successive
solutions of the salts, takes place. In consequence, there is formed at those places
of the surface a tougher and more watery substance. The latter causes the salt-
solution to descend on to the surface of the metal, whereas the tougher substance
surrounds the solution on the surface.
The following actions take place :
As soon as the solution of oxide of copper touches the iron, a protecting cover of
metallic copper is formed, and at the same time, through reciprocal action, ferrous
sulphate is formed, which being transformed by the alkaline enamel into ferrous
oxide causes a colouring of the enamel, running from the deepest part to the
surface. The particles of green vitriol, as they become dissolved are changed by
the alkaline enamel into ferrous hydrate or ferrous silicate or borate, that is to
say, they are transformed into insoluble forms, augmenting from the surface
inwards.
The unstable lower oxides are quickly transformed into higher oxides and there
appears rust on the surface of the enamel, whereby the spotting desired is artificially
produced at the surface.
The difference of oxidations and spotting which is caused by the employment of
the salts above indicated and which can be varied by altering the size of grains or
by simultaneous addition of these compounds in the enamel, produces a colouring
and spotting of the enamel which gives a very good appearance and body to the
article.

page_text: .
Having now particularly described and ascertained the nature of my inven
tion and in what manner the same is to be performed, I declare that what I
claim is :-
1. The method of producing enamelled goods of steel or sheet-iron with one
covering of an alkaline enamel, substantially as described.
2. Obtaining oxidation and formation of spots by metallic salts in the enamel and
on the surface of the same, substantially as described.
Dated this 2nd day of November 1893.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.