Quote Originally Posted by Toffle View Post
The problem is that printing papers are not perfectly flat. There is often a bit of upward curl on the emulsion side. It occurs to me that giving the paper neg a little curl the opposite direction might be helpful... if the edges/corners rather than the center of the negative are in contact with the printing paper when setting the glass, there would possibly be less risk of movement.

That is why you use felt or foam on the bottom.