Improvements in the Production of Enamelled Iron Ware.
Year: 1891

page_text: Date of Application, 29th Dec., 1891-Accepted, 30th Jan., 1892
COMPLETE SPECIFICATION.
Improvements in the Production of Enamelled Iron Ware.
I, HUBERT CLAUS, of Thale in the Harz, Germany, Managing Director of the
Thale Iron Works, Limited, 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 enamelling of iron ware by the
combination of processes which produce an enamel coating of great durability
together with considerable beauty of colour and a brilliant glaze.
A good enamel should at the same time be durable and beautiful, without either
property being decreased by the other..
The durability of an enamel coating depends on the union of the enamel with
the metal, on the elasticity of the enamel itself, and on the thickness of the layer
of enamel applied, which should be thin enough to be flexible and thereby increase
the power of resisting the deformation of the metal by differences of temperature,
pressure and the like.
In order to obtain the aforesaid objects, two processes are generally employed.
The iron either receives a single thick coating or two or more thin coatings
which impart to the article the required beautiful exterior and a very desirable
polish.
The enamels for a single coating are such that an oxidation is produced upon the
metallic ground-work which causes speckles in the enamel and is designed to give
the article a mottled appearance.
These enamel coatings must be transparent, in
order that the speckles shall be visible.
In the composition of the enamel the alkaline ingredients are reduced in quantity
so as to allow the enamel to contain the necessary free acids and to obtain, after
melting down, a completely glazed mass which can be considered a hard glass.
The enamel layer to be applied must be of a definite thickness if it is to fulfil
the object of giving the article a beautiful exterior and good polish; when only a
thin layer is applied the iron ground surface would impart its own dull colour to
the translucent enamel. With the thickness of the layer of enamel applied however
the defects due to the glassy brittle nature of the same, increase.
A sufficient addition to the enamel of such metallic oxides as would materially
heighten the durability is precluded by reason of the colouring action of the same,
whereby the transparency and the mottled effect produced thereby would be lost.
A slow cooling of the finished articles does not alter the physical properties but
only diminishes the existing brittleness.
The second process, for combining great durability with beauty of surface by
applying two or more thin elastic coatings which are fired singly, enables me to
give as a first enamel coating the so-called ground enamel, which. forms a firm,
perfect union with the iron and serves as a connecting link betw en the metal and
the subsequent covering enamel. This ground enamel is an elastic soft composition,
which may be mixed at will and according to requirements with metallic oxides,
such as nickel oxide and cobalt oxide, which, as shown by experience, materially
increase the durability of the said enamels.
The ground is applied very thin and by the burning is caused to enter the pores
of the metal with which the metallic oxides form alloys. The object of the further
coatings is to cover the ugly, dull, dark ground, and to give the exterior the desired
glaze without decreasing the great durability.
It is clear that this object is attained the more perfectly the more the covering

page_text: material, the so-called covering enamel possesses the property of great covering power
and durability when the layer is extremely thin.
In carrying my invention into practice I proceed as follows.
After the articles to be enamelled have been coated in the usual manner with the
ground which is rich in metallic oxide, a covering material is prepared consisting
of 45 parts of felspar, 10.parts of granite, 14 parts of sand, 16 parts of cryolite,
20 parts of borax, 2 parts of saltpetre, 3 parts of kaolin earth, and 3 parts of tin
oxide, the whole being intimately mixed together in a finely powdered state and
melted.
When the mass has been ground to a fine paste with water, clay being added
until it may be spread in a uniform coherent thin layer, I add to 20 kilogrammes of
the mass, 250 grammes of nickel sulphate and 50 grammes of cobalt sulphate and
mix the whole intimately on a porcelain slab.
The covering enamel being ready for coating the articles are after grounding
covered with an extremely thin layer. While the enamel is still moist the article
´is powdered over with calcined pulverized ammonia soda, through the medium of a
sieve either by hand or by mechanical means, then dried and fired as usual, thus
obtaining a beautifully mottled glaze tinted over with greyish blue pearl spots
of intense polish, and a fine general effect is secured together with great
durability.
The action which causes these interesting phenomena may be explained as
follows: The soda forms with the nickel sulphate and cobalt sulphate insoluble
carbonates NiCO, or CoCO. These amorphous compounds have the tendency of
absorbing from the surrounding substances dissolved cobalt sulphate and nickel
sulphate either purely mechanically or with chemical action in order to form basic
salts 2 CoCO, +3 Co(OH), or 2 NICO, + 3 Ni(OH),. By this means the colouring
principle is withdrawn from the materials surrounding the separated carbonates and
accumulated at a central point.
In this reaction is however produced at the same time sodium sulphate
(CoSO, CO,Na, = COCO, + Na,SO₁) which quickly takes up water of crystal-
lisation. This is withdrawn from the enamel, whereby currents are caused therein.
By reason of the molecular motion undulations are produced and formations occur
which extend in fine ramifications through the contracted enamel, producing
beautiful designs in the same and also increasing the durability by the presence of
the aforesaid metallic salts, and increasing the covering power by the formations
and marblings produced upon the surface, so that an extremely thin layer is
sufficient for covering the ground.
The articles thus enamelled are of great durability, resist acids and are suitable
for various purposes.
For special purposes, more particularly for resisting the action of chemical
agents, the articles are coated with a material made of felspar, fluor spar, quartz,
borax and saltpetre with such a thin layer that the coating is merely a film which
does not diminish the adhesion but produces an almost absolute power of resisting
chemical agents.
The manipulations can be carried out simply, rapidly and surely. As the enamel
is applied only in quite thin coatings and adheres like a fine paste it is sufficient to
simply immerse and swing the articles.
Other metallic salts which form insoluble carbonates are also adapted for
producing similar formations in and properties of the enamel, such as for instance
copper, chromium, iron and manganous salts.
The employment of the above-mentioned metallic salts gives a most useful
colour with great durability and high polish.
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 :-
The process for obtaining mottled enamelled iron ware in grey, bļuẹ or white

page_text: marbling or other tints by producing thereon chemical actions, substantially as
herein described.
Dated this 29th day of December 1891.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, Agents for the Applicant.