Dear jsimoespedro,

The "unpolished" glass is there so that you don't see Newton's rings caused by putting the smooth side of the film against smooth glass. Obviously there is no issue with the emulsion side against smooth glass.

Glassless negative carriers are much more common and you will see lots of arguments about the merits of both if you search the archives. I made a small and quite unscientific test for myself once and found that the glassless carrier (4x5 negative) made no improvement that I could find. By the same token, a better printer with a better eye might find glass carriers a necessity for producing their best work.

Neal Wydra