[ATM] processing techniques for soft optical glass?

[David Weinshenker <daze39@earthlink.net>]

So I've been poking around in glass catalogs and running
a few computer searches for good pairs and triplets
(in terms of accurate "curve match" across the spectrum)...
and it turns out that the glasses that tend to show up
in the most desirable pairs - e.g., the interesting
"fluoride" crowns and many of the "special dispersion"
flints - seem to be rather soft, soluble glasses with
low resistance to abrasion, moisture, and chemical
attack.

("Is that glass, or rock-salt?")

It occurs to me that trying to "hog out" the curve on
a small lens (e.g. 2" diameter) of such glass (against
a corresponding glass tool which was to be generated
to the matching shape in the process) might work badly -
too much of the soft lens glass might be ground away
by the time the tool (of hardener "ordinary" glass)
had the desired radius.

An alternative method that occurs to me would be to
use two "plain" glass tools, oversize relative to the
lens - say 4" diameter "boro" or "soda" glass disks
for a 2" lens - the process would be to grind them
against each other (with a suitable combination of
the usual sort of radius-generating and smoothing
strokes), progressively working them toward the
target radius while alternately grinding the lens
glass against the appropriate tool of the pair.

Each tool+tool grinding session would deepen the radius a bit
and bring the tools to good spherical contact at that radius,
and then the ssmaller lens would be ground against the tool
(with a stroke designed to  equalize wear over the surface
of the larger tool) until it was in full contact at the new
radius.

Does this sound like it could work well? Would there be
any virtue in using a fluid other than water for suspending
the abrasive grains (perhaps a light mineral or fluorocarbon
oil) which would have less of a solvent action on the glass?

-dave w
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