New or Improved Method and Means for the Decolourization of Glass.
Year: 1899

page_text: Date of Application, 26th Jan., 1899-Accepted, 18th Nov., 1899
COMPLETE SPECIFICATION.
New or Improved Method and Means for the Decolourization of Glass.
I, RUDOLPH MOSER, of Karlsbad Glass Works, Meierhofen, Karlsbad, Bohemia,
in the Empire of Austria, Glass Manufacturer, 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 agents hitherto employed for the decolourization of glass by the removal
of the green tint due to the presence of iron are very impracticable and seldom
produce the desired result. Either over or under colouring is easily produced
and in the few cases where the desired absence of colour is produced it is generally
by accident or as a result of conditions which it is difficult to reproduce. Even
when the wished-for result is obtained it frequently happens that either after
cooling of the glass in a tempering furnace or by the action of the sun's rays upon
the finished product the effect of the decolourizing agent partially disappears and
a coloured tint of greater or less depth appears.
It has been proposed to decolourize glass by the addition of selenium, selenate
or the like with or without the addition of other decolourizing agents, but the
defects enumerated above are not thereby obviated
The object of employing selenium and its compounds for decolouring glass
is to neutralize the complimentary green of the glass by means of the red.
colouring properties of such substances. Glass which has been decolourized by
means of selenium and its compounds alone possesses a reddish tint in the first
place or assumes such a tint under the influence of the sun's rays.
Apparently for the purpose of reducing the amount of selenium to be employed
(this substance being invariably costly) a process has been suggested in which first
of all other decolourizing agents are employed, selenium being thereupon added
for the purpose of increasing the whiteness of the glass.
It is therefore obvious that it would be of enormous advantage to the glass
industry if glass could be decolourized by means of a suitable process in such a
manner that the appearance of any colouration is completely obviated. Now I
have found that by mixing various bodies in special and predetermined propor-
tions the selection of such bodies being determined with a definite object it is
possible not only to produce colourless glass in a sure and certain manner but also
to impart increased brilliancy to such glass.
The selection of the said bodies and their employment in suitable proportions
for the purpose of decolourizing glass forms the subject of this invention.
In order to carry my improved process into effect I mix together manganese
peroxide, selenium, oxide of bismuth, protoxide nickel hydrate, and arsenious
acid, advantageously in or about the following proportions viz.:-
30 parts of manganese peroxide.
25 parts of selenium.
20 parts of oxide of bismuth.
15 parts of protoxide nickel hydrate.
10 parts of arsenious acid.
This mixture is added in a suitable manner to the molten glass.
[Price 8d.]

page_text: The said mixture is of a lead grey colour and when finely ground it forms a
reddish or black brown powder; if it is not to be used directly after its manu-
facture it should be kept in a closed glass receptacle in a cool and dry place.
The quantity of the said preparation which should be employed for decolouriz-
ing glass is arrived at for each melting pot by taking into account the composition
of the glass, and also the working of the furnace, the method of heating, the
temperature of the furnace, the special melting process employed in each glass
amanufactory, the duration of the melting operation, and so forth.
For every 100 kilogrammes of glass to be produced from 5 to 25 grammes of
the powdered mixture should be intimately mixed with about 2 kilogrammes of
the material from which the glass is to be made.
The compound which has thus been prepared in a glass mould is introduced into
the melting pot after the melting has proceeded to some extent in the furnace;
the mass in the melting pot is then by means of the insertion of wet sticks of
wood or other vegetable substances (vitreous arsenious oxide being added if desired)
brought to a state of ebullition in such a manner that the various strata are mixed
to the greatest possible extent.
The proportionately large addition of oxide of bismuth to the above mentioned
preparation if carefully mixed with the remaining constituents of the powder
imparts increased refractive properties to the glass, whilst the presence of arsenious
acid is adapted to obviate over colouring and also any tendency in the glass to
become tinted subsequently.
If taken separately or mixed directly with the glass mixture the constituent
parts of the preparation would not produce the desired result and it should like-
wise be remarked that with any decolourizing agent hitherto known so small a
quantity would not be sufficient for decolourizing glass as is the case with my
preparation whilst no other decolourizing agent is adapted to impart increased
brilliancy to the glass.
In the manufacture of the preparation used for decolourization the proportions
of the separate constituent parts may vary to a limited extent from the percentages
named above.
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―
1. A process for decolouring glass consisting in the addition thereto, during
the melting thereof and in or about the proportions specified, of a mixture com-
posed of 30 parts by weight of manganese peroxide, 25 parts by weight of selenium,
20 parts by weight of oxide of bismuth, 15 parts by weight of protoxide nickel
hydrate and 10 parts by weight of arsenious acid.
2. The herein-described process for decolouring glass which consists in the
addition thereto at the time and in the manner and quantity specified of a mixture
or preparation of manganese peroxide, selenium, oxide of bismuth, protoxide nickel
hydrate and arsenious acid in or about the proportions stated, mixed together,
and then mixed with a portion of the materials from which the glass is to be
made, and added to the molten glass, substantially in the manner and for the
purposes set forth.
TONGUE & BIRKBECK,
Southampton Buildings, Chancery Lane, London, W.C.,
Agents for the Applicant.