I have recently been asked to make contacts and then enlargements of some negatives from the late 1920s/early30s. The negative material is very thin and prone to curling. I will need to manufacture a carrier for the negatives and incorporate glass to keep them flat. I have never enlarged with glass carriers, and so even though I have heard of newton rings and anti-newton glass I need some info on what causes newton rings and what makes the glass special. I do contact print large negatives with a glass plate, but have never had a problem. I assume that it has something to do with the glass changing the light path before it reaches the lens, causing some sort of aberation. Is there a retail source for the glass? It does not have to be exact size, if the size is larger then what my carrier requires I can have it cut down here. Finally, I think I have heard of an anti-newton glass cleaner, or spray or some such thing. Anyone familiar with this product or if it works?