Ed Huntress prodded the keyboard with:

On Thu, 30 Apr 2015 18:16:06 -0700, wrote:

On Thu, 30 Apr 2015 15:57:05 -0700 (PDT), Gerry
wrote:

On Thursday, April 30, 2015 at 5:25:46 PM UTC-5,
wrote:
Not exactly metalworking. I needed to make a replacement glass
piece for a camera because I removed the IR/UV filter and the
space needed filling for proper focusing. I used a 1mm glass
slide, the type made for microscopes. The piece needed to be 8 x
9 mm. I mamaged to get one and then discovered I had scratched
it. So I tried again and was rewarded with a scratch free piece.
I was surprised how hard it was to cut this glass, for it to
break where I wanted it to, and finally figured out how to score
it properly. I hope I never need to do this again.
Eric

Years ago I did lapidary work. While most everything was done with
stone I used to play with glass sometimes. I was able to cut glass
with a diamond saw, grind to shape using grinding and sanding
wheels with water drip to keep things cool. The glass was mounted
to dop sticks using what was called dop wax which was almost like
old style sealing wax used with stamps for letters and such. Maybe
you can find someone close by that is into lapidary work for help?
A designing jeweler may point you in the right direction. I'd bet
that your local glass shop has wet belt sanders with different grit
belts for finishing glass edges. Maybe they would let you use their
belt sanders for your project?
Greetings Gerry,
I have done lapidary work and even have the stuff still to do it. My
stone saw is just not set up to cut stuff so small and the glass is
more brittle than the stones I have cut in the past. I did finish
off the piece by using one of my diamond wheels on my slow speed
carbide grinding/lapping machine. I was actually surprised at how
fragile the glass was. I have cut glass tiles in the past year with
one of my diamond cutting discs cooled and lubricated with water and
had no trouble. But the little pieces I just did were much more
prone to chipping and cracking than the tiles and the diamond
cutting disc caused too much edge chipping, even when run quite
slow. Thanks,
Eric

Microscope slides are soda lime glass. If you had some Corning
slides, they used to be tempered -- probably, they still are.

Although tempered glass is strong, it gets its strength from being
pre-stressed in a way that increases bending strength but also can
make it prone to chipping as the stresses are relieved. Generally,
the chips are quite large; you've probably seen how tempered car
windows shatter into pellets, rather than into sharp little shards.

All of that may be of no help in understanding what you're running
into, but be aware that there are different grades and they may
break in different ways.


In all probability the glass needs anealing. Heating up to red and a
very slow cooling down. Bottles & such take 8 to 12 hours, but they
are much thicker than a microscope slide.


--
Best Regards:
Baron.