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.