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.

[Konical]

Good Afternoon, Hoffy,

HenrySamson has it exactly right. 1/4 inch glass is preferable because its weight helps flatten negatives, and it's less likely to break than the 1/8 inch stuff. Mine is also oversized at around 11 x 14, a bit larger than Henry's, mostly to increase the weight slightly.

Konical

[hoffy]

Thanks for all the comments and replies. I will go for the 6.5mm glass and take it from there.

Cheers

[77seriesiii]

alright this topic seems to have answered a question I had and raised a few more.

I have an 11x14 contact frame, Century made and it needs glass. Based on this discussion I should get antiglare and thicker than 2mm. For this contact frame, how thick should my glass be? I understand that some of you are using super thick glass which has the weight enough and eventually I will probably go that route but I have a gadget and I want to use it! ;-)

Thanks

Erick

[Loris Medici]

77seriesiii, ordinary 2mm glass will do the job for your 11x14" contact printing frame. I have one from Bostick and Sullivan (same size as yours, actually oversized for allowing brushmarks and white space around the image) and use it for different alternative processes w/o troubles. I broke its glass twice before, and I just replaced it with ordinary glass from glass shop w/o any adverse effects. (Have them file - if that's the correct term for glass - the edges and corners to eliminate the risk of self harm while handling it!) I always pay attention to keep a spare glass in case of an accident... I sometimes see Newton rings, but they don't seem to register in the prints. (Maybe UV light - which is what I use for exposures - is less affected from newton rings...)

[77seriesiii]

Loris,

I use the same glass, mine just cracked the other day so I was wondering if I needed something different. I have seen newton rings in the glass as I move around the frame and like you they havent registered. Also, like you, I am using other processes, right now I am trying to print consistently with vandyke browns, so far no two prints are alike. One day, I'll nail it.

Erick

[nick mulder]

By just using the weight of the glass how do you go about looking at your print without losing registration like you would with a split frame back ?

I use one with POP processes and often enough with DOP also as there can be some hints in the initially exposed paper (solarization around the film edges for instance).

[henrysamson]

By just using the weight of the glass how do you go about looking at your print without losing registration like you would with a split frame back ?

I am a contact printer who just uses the glass but I am printing on photographic paper so there is no need to inspect (nothing to see anyway). I would not think that using just glass, as opposed to a split frame, will be suitable for processes such as POP paper or platinum or any of the other processes that require inspection.

[bwfans]

How about use a scanner glass? I have a few scanners or those multiple function printers all with glasses. Are they better for the contact printing purpose because they are actually designed with image copy/scan in mind?

[Loris Medici]

Applies to UV processes only: Scanner glass will do the job IF it's indeed glass! ;) All the flatbed scanners I've used (and seen) were fixed with acrylic lids and AFAIK acrylic isn't as transparent to UV as ordinary glass...

OTOH, even if your process doesn't need UV light, be warned about the fact that acrylic is way lighter than glass, therefore you'll loose some pressure which may translate as unsharp contact prints...

Regards,
Loris.

[holmburgers]

Applies to UV processes only: Scanner glass will do the job IF it's indeed glass! ;) All the flatbed scanners I've used (and seen) were fixed with acrylic lids and AFAIK acrylic isn't as transparent to UV as ordinary glass...

OTOH, even if your process doesn't need UV light, be warned about the fact that acrylic is way lighter than glass, therefore you'll loose some pressure which may translate as unsharp contact prints...

Regards,
Loris.

Reviving an old thread...

I think the opposite is true about acrylic transmission of UV. See here.. http://www.fresneltech.com/materials.html

Making an acrylic (plexiglass) or polycarbonate contact printer would be great for alt processes. Since it's lighter though, I wonder what thickness one would need to provide substantial weight for holding things flat, and if that increase in thickness would negate the boost in UV transmittance (I suspect it wouldn't). Or alternatively, if you designed a printer with even pressure around the edges you could probably get around any issues from the weight difference, but rigidity would become just as much of a problem.


update: something like this -> http://www.spartech.com/polycast/solacryl.html