Re: Print Frame Glass Quality -Forwarded

Richard Knoppow (dickburk@ix.netcom.com)
Tue, 07 Apr 1998 01:52:10 -0700

At 02:38 PM 4/6/98 -0600, Bob_Maxey@mtn.3com.com wrote:
>
>>> Is
>> there such a thing as "optical quality" glass? How is optical quality
>glass
>> manufactured?
>
>Optical quality is a term that is often applied wrongly. Yes, true optical
>quality glass is available - there are a number of specialty glass
>manufacturers that can provide it. The manufacturing process is basic to
>all glass; that is, a float type process is used. However, the raw
>materials are extremely pure, carefully measured and the process is very
>carefully controlled.
>
>RM
>
I believe what you are describing is the technique for making plate
glass. If my memory is correct, ordinary window glass is made by rolling,
something like sheet steel. Rolling often leaves irregularities in the
glass making it unsuitable for some purposes. Plate glass has smoother,
more parallel, surfaces and tends to be more homogeneous than rolled glass.
The term "optical glass" usually refers to glass formulated to have
specific optical qualities, i.e. index of refraction and dispersion, for
the purpose of making lenses or other optical components. Optical glass
must also be homogeneous and free of dirt or impurities.
Filters are sometimes made with optical quality glass, meaning the sheets
are ground flat and parallel, and the glass itself is chosen to be
homogeneous. Optical glass for lenses is made in pots. When the glass has
cooled the pot contents are broken up and the individual pieces treated in
various ways to make lens blanks. Some types of rare-earth glass must be
made in pure Platinum pots.
----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com