Contact printing glass. How thick?

[hoffy]

Hi,

I want to improve the way I make contact printed proofs and also potentially do some contact printing of paper negatives.

I am trying to source some frosted anti glare glass, but can only find the gear that the picture framers use (2mm thick). My concern is that this may not be heavy enough to hold everything flat. Would this be OK? Or would I be better off trying to source something that is a bit heaver? OR would it work if I layed two layers of glass on top of each other?

Cheers

[nick mulder]

2mm - I'd be concerned is too thin for anything larger than maybe 4x5 or 120 sized frames...

Upon applying pressure on some 3mm think glass over around an 8x10 area I cracked it and scratched up a neg quite nicely.

Frosted anti-flare huh ? Out of interest, what is the thinking behind that ? Even with a diffuse source like a bank of UV flouros I find that the emulsion is so close to the paper that resolution is maintained, under direct sun with its collimated nature and lower 'profile' it is ideal - I would have though any frosting would be either redundant or even harmful if you were using the sun and there wasn't enough contact pressure ...

I just use a slab of 5mm glass from the local window chaps - doesn't seem to affect exposure times under UV lights that much, 30secs in Pt/Pd for instance

[henrysamson]

I have been making contact prints for years just using a sheet of 1/4 inch glass bought from glass shot. Negatives up to 8x10. It is the thick stuff used to make coffee table tops. No need for frosted. The weight of the glass holds everything in place fine, no frame needed. No Newton's rings either. My piece is 10x12 so I have an inch all the way around for finger prints. Have them grind the edges so it is not sharp.

[hoffy]

Thanks.

The frosted? Because thats what I have seen been used here (I did a search). So are you suggesting that I use just a standard piece of glass?

[Jeremy]

I just use standard 1/4" clear glass.

[nick mulder]

Yup, frosted will just reduce the transmission ...

No benefit that I can ascertain - but I can see how some faulty logic or a misunderstanding may have made it a suggestion in that perhaps they were trying to reduce the chance of banding and had some diffusion installed closer to the lamps

[Sal Santamaura]

"Non glare" glass is used in contact printing frames to eliminate newton's rings. Get the finest pattern your picture framing supplier has; single-sided is fine. Make sure they cut a defect-free section and remember to put the rough side toward your negative.

If you've never struggled with newton's rings, congratulations! Keep using plain glass when contact printing. If you have been frustrated by this problem, using "non glare" glass will bring great satisfaction.

[Lopaka]

I have never encountered newton's rings in this context...
I just went to a local custom glass shop and ordered a piece of 1/4" thick glass cut to size with the edges sanded, so there would be no sharp edges.
Works fine.

Bob

[JBrunner]

Newton's rings are most prevalent in humid climates, and also when positive contact pressure isn't fully maintained. IME it seems more prevalent with some papers than others. They are caused by any small, even microscopic, gap between the negative and the glass, whether air or moisture. With regular glass, a felt or foam backing and good pressure like in a contact frame goes a long way to eliminating them, but not always. With the frosted glass they are eliminated by the scattering of the light, removing the "harmonic" in the gaps that cause them. Exposure time is generally not a problem with contact printing, even with the slowest of paper, so the minor loss of transmission isn't generally anything to notice. I printed with regular glass for a long time, and never thought I had a problem. One humid summer they appeared in droves. I switched to the frosted no-glare glass and they disappeared. Careful examination of earlier prints after the fact revealed earlier, but nearly unapparent manifestations of the same issue. I personally won't use any other kind of glass now.

My 8x10 spring backed frames have 2mm glass, sourced from a framer. Larger glass for larger prints I had etched at a glass shop, and is 3/8ths inch. I don't know how many mm that is, I live in Utah.

[jmcd]

I have not had a struggle with Newton's rings, and also use a 1/4" piece of plate glass from the local shop. I use this for proofs and for contact sheets.

Laminated glass with eased edges would be hard to break and should do a good job, also.

If I ever get Newton's rings, I will pursue the non-glare glass solution. I bet this is available in a laminated sheet.

As Sal mentioned, be sure to tell the shop what you are using it for so they select a section without scratches or other defects.