Quote Originally Posted by George Nova Scotia View Post
Interesting that Edmund said the HA glass could be cut - that would indicate it's not tempered, but it could be cut and mounted much like the round piece I have but better.
Quote Originally Posted by Jeff Bannow View Post
The lady that emailed me could also have just been wrong about cutting it. Not sure there.
I have seen both tempered and non-tempered heat absorbing glass filters advertised on more than one page. For example, if you look at this Hoya page:


you will notice they talk about "'Strengthened glass', produced by tempering processes, may also be supplied", suggesting they have both types of products for sale.

Not sure how vital tempered glass is in a high powered enlarger head like the Ilford 500H, or if it could be swapped with non-tempered without major issues. Maybe Ian C can comment on that. Since the filter is very close to lamp, I can imagine issues.