There is a glass that seems to be slightly frosted and used for framing. You can find it at Joann Fabrics, Michaels, or I'm sure other framing shops. I forget the exact name of the glass, but ask to see samples of their selection and you can easily pick it out. It has a very faint and fine frosting to it.
That's the glass, I was talking about. It's the anti-glare picture framing glass. It should work above the negative.