Improvements in the Manufacture of Rose-red Glass.
Year: 1893

page_text: Date of Application, 24th Aug., 1893-Accepted, 4th Nov., 1893
COMPLETE SPECIFICATION.
Improvements in the Manufacture of Rose-red Glass.
We, HEINRICH RITTER VON KRALIK and WILHELM RITTER VON
KRALIK, trading as Wilhelm Kralik Sohn, of Eleonorenhain, near Strakonitz,
Bohemia, in the Empire of Austria, Glass Manufacturers, 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 :-
This invention relates to the process, discovered in 1865 by the French chemist
J. T. Pelonze, of staining glass a rose-red colour by the incorporation into the
ordinary glass-composition of free or metallic selenium. In carrying out this
process, the selenium is either added to the mixture of raw materials to be filled
into the melting pot, or it is introduced into the already molten mass.
There are two grave objections to this process, namely, a great part of the costly
selenium becomes vaporized and burnt under the action of the high temperature
prevailing in the glass-melting-furnace, and the selenium of commerce is always
accompanied by impurities such as copper, iron, etc., which interfere with the
colour of the glass and cannot be separated from the selenium except by a tedious
process.
According to our invention these objections are overcome by adding either to the
batch or to the molten glass composition suitable selenites or selenates instead of
metallic or free selenium and by decomposing these salts by the introduction of a
convenient reducing agent after they have been completely dissolved in the molten
mass.
We thus replace the easily inflammable metallic selenium by substances which
are very steady under high temperatures and in preparing selenites or selenates of
the selenium of commerce the impurities are necessarily at the same time eliminated.
Consequently a better result is obtained at less expense.
In practice we find it preferable to use the selenites or selenates of alkalies or
alkaline earths; it is obvious, however, that other salts of selenious or selenic acid
may be used provided with the bases of these salts do not give a wrong colour to
the glass.
The selenites or selenates chosen, which in most cases will be the potassic, sodic
or calcic salts, are either mixed with the batch or added to the molten glass mass,
and in both cases the molten mass is well stirred up in order to obtain a uniform
distribution therein of the dissolved salt or salts.
As soon as the selenite or selenate used is wholly dissolved in the mass, a quantity
of a reducing agent corresponding to that of the added salt is introduced into the
molten mass, which is again thoroughly stirred up. The reducing agent may be
arsenious acid, arsenite of soda or potash, sulphite of soda, etc., but in general zinc-
dust is preferred. The selenium separated in this way gives the desired rose-red
colour to the glass.
The quantity of selenates or selenites to be added to the glass composition or to
the molten glass depends on the desired depth of colour to be given to the glass,
and is best found out by a preliminary experiment on a small scale. In most cases
two or three per cent. of selenium will suffice.
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 :-
1. The manufacture of rose-red glass by adding selenites or selenates to the
glass-composition or to the molten glass, allowing the salt or salts to dissolve in the
molten mass, and finally decomposing it or them by the incorporation of a suitable

page_text: reducing agent, which sets the selenium free, substantially as hereinbefore
described.
2. The manufacture of rose-red glass by adding potassic, sodic or calcic selenites
or selenates to the glass batch or to the molten glass composition, allowing the salt
or salts to dissolve in the molten mass, and finally decomposing them by the
incorporation of zinc-dust, substantially as hereinbefore described.
Dated this 24th dox of August 1893.
G. F. REDFERN & Co.,
4, South Street, Finsbury, London, Agents for the Applicants.