[ATM] Grinding Question, and the color of Pyrex

["Russell Jocoy" <russjocoy@hotmail.com>]

    My first reply is to Darius Blaszijk, and his question on "grinding"... 
Did you grind out the center of your disk with a rotary grinder?? This is 
what I took on your first posting...
   If this is the case, keep your tool on top for awhile and work to the 
edge. What ever your "SAG"
turns out to be will be... Never dig a hole in a mirror with a power tool 
unless it is guided by some
form of radius guide or pendulum.. If you were hand grinding, disregard my 
statements.
     Tool on top , and different strokes can bring the deep curve back up, 
but if you have ground a
hole in the middle, it might take  a while........ If this is your first 
mirror don't concern yourself with
the saggita until you get a spherical surface,  You need to work the curve 
out to the edge..
Once you do this then measure.. make sure you bevel the outside diameter of 
your disk..

     Jerry...    The color of Pyrex.... I have had the privledge to have 
many different slabs of Pyrex
glass pass through my hands. Some of this was large 4 foot by 5 foot by 1 
5/8" slabs, and some
scrap cut off's. Some also being 7/8" thick..... I have seen color 
difference in separate pieces, from
"straw color" to "white color"   The large 1-5/8" slabs were towards the 
yellow side, ( althought
I had some 10"x 40" cut off's that were noticably white. The 7/8" sheet that 
I still have, 4'x5',
is white as can be.   As far as annealing I find no stress in either color., 
As far as cutting I have found
no difference in hardness. My guess is either an imperfection in the mixing 
process or a chemical
action at a certain temperature. This is a great question that only Pyrex 
manufacturer's could answer.
   I see no difference in the material, just the color....    Russ Jocoy


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