Please note that my post referred to film's emulsion side contacting bottom glass in a negative carrier. With contact printing, your rings are coming from the film's base side touching frame glass. Every sheet film I'm aware of does that (except 320TXP, which has a dull base-side retouching coating) and almost demands anti-Newton glass when contact printing. This also applies to a glass negative carrier's top glass. All of my enlarger glass carriers are configured with plain bottom and anti-Newton top glasses.
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