I can't begin to tell you how thrilled I am today!!!
Finally I solved my Newton Ring problems. I was using a newly made vacuum frame, and the Newton Rings became very noticeable in the mid-tones. Highlights and shadows were not much of a problem. I priced anti-glare glass, but it was far too expensive for me (11x14 $65)...
I decided to try a piece of frosted glass (24x25 $34), and it worked fantastic. The Newton Rings are not merely diminished, they are completely gone now. The side of the glass which is frosted adds a slight texture, and also defuses light evenly, so it was perfect for my purposes.
Now I can get back to printing my photos, and get out and take some new ones!