Quote Originally Posted by nomennominatur View Post
I am aware that anti Newton glass should display some roughness, however, neither with naked eye, nor with a 10x loupe am I able to discern any roughening. However, I do not get any Newton rings at all, sandwiching the film without any spacers. I am a bit puzzled myself. The glass is from a rather prestigeous framing shop out of town. Next time I go there, I will ask the owner about the technical details of this archival glass, which he uses only for the most expensive framing jobs. The glass is rather thin, thus the top glass does not brutally weigh down the negative, yet flatness is more than sufficient for my DOF setting.

Kind regards
Mathias
Perhaps your museum glass is the type with an antireflective coating on it? If so make sure you clean it like you would a camera lens. I have a few sheets I've tried in the enlarger and they seem to do a decent job with newton rings on most of the time.