Re: [ATM] Pyrex ? Borofloat?

[David Weinshenker <daze39@earthlink.net>]

hermit wrote:
> horace r davis wrote:
>> So far I picked up13.5 lb of pyrex at second hand store for $7.45 some of
>> the double boilers have pyrex with a slight color can I mix them or does
>> the glass have to be 100% see transparent. 
> Well, transparent is nice for a lens.  Pyrex normally has some color 
> though.  So, even for a lens, it shouldn't matter too much, depending on 
> application of course.
> 
> Ken Lowther

I recently got some "borosilicate sight glasses" (round disks 3/4" thick
by 4" diamneter) from McMaster - the catalog says that it's either "Pyrex
or Schott" glass; I strongly suspect that these particular disks may be
Schott "Borofloat" rather than Pyrex 774... Schott claims BF is more
transparent than Pyrex, and these seem to be perfectly "water-clear",
even looking edgeways; Pyrex always seemed to have a little bit of a
grayish tinge by comparison (and conventional plate glass is noticeably
greenish when thus viewed).

Like Pyrex, the refractive index is in the 1.4's, and there doesn't seem
to be anything really interesting about its dispersion characteristics
(although I should toss it in my "achromat search" code just to see what
happens...) so it doesn't seem like there's any particular optical reason
to use it for a lens, but if there was a need for, say, a lens element
that was exposed to hostile environmental conditions, the uniformity and
transparency should be good.

Schott lists available sizes up to 1 inch thick - it might be useful for mirror
blanks in the 6 to 10 inch diameter range (more if one wanted to do the "thin
mirror" thing...)

Kiln-fusing a stack of sheets to make a thicker blank might work,
but how could discontinuities in the final mass (from where the
layers melted together) be avoided?

-dave w
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