Quote Originally Posted by Steve Sherman View Post The previous
post didn't work out to well.  I used to use a piece of 1/4"
plate glass with not frame. In using Azo I found the printing
time quite long. Just happened to switch to a vacuum frame which
uses a piece of clear 1/8" glass, the printing times were
significantly shorter with the same negatives. I asked a glass
person why and he said that plate glass is inherently stronger
than ordinary glass and actually has a light reducing effect, he
simply asked if the sides of the glass were at all green, that
is an indication of "plate" glass which reduces light
transmission.  Also, Azo is largely sensitive to UV and glass
tends to block UV - that's why UV lenses are made of quartz. I'd
bet that if you were using ordinary enlarging paper, you
wouldn't see nearly as much difference between the 2 pieces of
glass.