Naturally, now that I need to link to it I can't find a fairly recent discussion on center filters in which a poster said that Schneider's aren't sandwiches but have something dark sputtered on a surface.
I can't address all of the sizes etc. of CFs that Schneider made, but here https://web.archive.org/web/20200403...r/401990882024 is one that's separated and showing Newton's rings. It has to be a sandwich.
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