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PHOSPHATE OPAL GLASS
FOR LIGHTING GLASS (PR 437)
- finished in 2000
Aim: an non-polluting, white opal glass
The aim is to produce an opal glass with properties which suit
the production of lighting glass. The opal glass shall be non-polluting
from a melting and working point of view by being fluorine-free
and adjusted to thermal expansion for the non-lead clear glass
which is produced today.
Increased awareness of the
environment and raised demands
The increasing awareness of the environment, combined with raised
environmental demands of the authorities, has made the glass
industry to try to minimise the use of raw materials which affect
the environment.
Use of fluorine by tradition
A traditional opal glass is produced by adding different raw
materials containing fluorine.
Fluorine has been used in the
glass industry as it functions as an effective melting accelerator
and as it easily gives a dense and white opal.
Fluorine has also been used as
an additive to many other glass types than just opal glass. For
these other glass types the addition of fluorine is almost eliminated
and has been replaced in a satisfactory way. Besides the environmental
aspect there are many other disadvantages of using fluorine.
The use of fluorine means emissions
inside as well as outside the glass-house. Even though the authorities
not yet have specified the limit value for fluorine it is desirable
to find solutions already now which will eliminate the use of
fluorine.
Opalizing process
Opalizing is caused by small particles whose refractive index
differs from surrounding medium. In principle there is of no
importance if the particles are crystalline or not. In the fluorine
opal a rapid and favourable crystallisation of calcium fluoride
occurs.
Alternative instead of fluorine
Up to today's environmental demands the advantages of fluorine
have outweighed. To produce dense and white opal glasses for
production of lighting wares for instance there is no real alternative
instead of fluorine to be found.
Publications
Literature studies have shown that there are only relatively
few details published on alternative opal glasses for lighting
purposes. For handmade art-glass industry or lamp production
there is no information at all about any possible alternative
production method.
The alternatives of today
do not function
The alternative opal glasses which until now are industrially
produced are different types of phosphate opals. However, these
glass systems are based on compositions with a high percentage
of boron oxide, normal levels between 12 and 14% B2O3.
Thus, the glasses have a low thermal expansion and may not be
combined with traditional glasses for handmade glass industry.
This type of glass is almost exclusively used for production
of varying technical glasses.
CURRENT PROJECTS
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