Is there a special glass used for contact printing?

[foton33]

Is it ok to use regular glass to make 8x10 contact prints in a contact print frame? I have been having some problems with newton rings(?). Those sort of rainbow rings that come up in the print sometimes. Any advice on how to get rid of those things? Is it a flaw in the glass that causes it?

[Gary Holliday]

The only advice really is to have everything clean and dust-free as possible.

[Monophoto]

Ordinary glass is fine.

Newton's rings are an interference pattern created when the contact between the negative and glass isn't perfect. The problem can be avoided by using special glass, by adding a fine powder between the glass and the negative (although that's probably not a great idea if you are making contact prints), or by making sure that the glass applies uniform pressure across the 8x10 print surface. The latter is the most common solution, and either involves using glass that is thick enough that the weight of the glass completely flattens the negative, or by using a contact printer with back springs to flatten the sandwich of glass, negative and printing paper.

[Curt]

Against professional advise I bought a sheet of "Optical Glass" which came with a certificate and number. I paid $80.00 so it wasn't cheap. I have not had a problem since I started using it. It's thicker than window glass and is a really a nice work in its own right.

Curt

[foton33]

thanks all, Jody

[Scott Peters]

I use glass from ace hardware with no problems whatsoever....cheap too. Regular window glass.

[dancqu]

I'll add to the OP's question. How about coated framing glass.
A frame shop informed me that they can frame using non-reflective
glass. I've thoughts it may also be good for a projection printing
frame. I've some really bent enlarging paper. Dan

[Nick Zentena]

I use plate glass for contacts without a contact frame.

For enlarging? Isn't that going to be like sticking a new element on the enlarger lens?

[dancqu]

I use plate glass for contacts without a contact frame.
For enlarging? Isn't that going to be like sticking a new
element on the enlarger lens?

An interesting point. A flat over a lens is not thought
of as altering the optics; filters front or rear. Do to the
intimate contact with the paper I doubt there would be
any problem. Interference patterns? Dan

[Nick Zentena]

Filters do shift focus. It may not be much. It can be very little for a very thin gel filter but to the best of my knowledge they do shift the focus. The Kiev fisheye lenses require a filter to be used. It's part of the optical design.