ATM Adventures in Strained Glass

[Roger Ceragioli <rogerc@dakotacom.net>]

Hi, Ralph.

Well, I can tell you that Dean Ketelsen broke a 20" blank last year while
coring out a hole in it for use as an autocollimation flat.  The blank was
old and showed significant strain.  I can also tell you that I tried to
figure a 6" disk of BSC2 optical glass (like BK7) last summer, that showed
strain and inhomogeneities.  After weeks of finger and thumb polishing, the
figure was still garbage and seemed to keep changing irregularly on me as I
rubbed different parts of the disk.  I chucked that disk into the garbage
and got another with excellent homogeneity and anneal.  Figuring was easy
and now I have a fun little 6" f/15 achromat.  Maybe it's coincidence, but
I'm convinced.

Roger Ceragioli