Quote Originally Posted by George Nova Scotia View Post
The C760 glass is 2mm thick. It almost could be made to fit but I'm not sure if it's tempered. From what I have read tempered glass is very difficult to cut and cutting/shaping destroys the temper near the edges. Maybe someone who knows glass can comment on the cracks in the rectangular piece and whether they indicate tempering.
The Ilford 500 manual says about the dichroics:

"The cut off frequencies of dichroic filters are affected by temperature, causing inconsistent results. To reduce this variation in transmission with temperature, the dichroic filters in the ILFOSPEED MULTIGRADE 500H enlarger head are tempered prior to use"

Now, correct me if I am wrong, from reading these Schott glass pages, I have the strong feeling Heat Absorbing (HA) glass, is actually just another type of dichroic filter glass with another spectral transmission pattern. So likely, the HA filters are tempered as well...