Contact printing glass. How thick?

[Mustafa Umut Sarac]

I think acrylic is wrong selection because it is very easy to scratch it , it will lose its surface smoothness with time and it is harder to obtain with desired sizes. And there are acrylic photograph frame glasses and they are very successful to block uv.


And what is the abbe number of acrylic and glass for uv ? I think acrylic could lose its flatness and would deform in time. Thick acrylic would be very expensive for you. Nobody cuts its full size acrylic for you. You can cast your glass with liquid acrylic and hardener but if your polymer is not fresh , surface would be covered with colored diffractions.


Glass is cheap, its easy to order a desired size , higher abbe and index number and you can clean it with your wet wipe. Acrylic would be sensitive to chemicals and you cant be sure whats inside in your cleaner.


Plastic flat panels are sweet for applications but obtaining them in small sizes are very hard because they are for industry.

[keithwms]

I use half inch at least. For silver contacts, my logic is that you want the top surface as far away from the print as possible, so that if there's any dust or surface defect on the glass it'll be diffused out, i.e., you only have to worry about the surface contacting the neg. Plus the added weight makes for some very nice flatness even with the matte papers I prefer. For alt contacts, the transmission may be an issue- a lot of glass cuts out at ~350nm. But it hasn't been an issue for me. So I say go with thick. If you need to do a lot of dodge and burn then you may want thinner so that you can control the light a bit more precisely.

[keithwms]

P.S. acrylic is *awful* for contacts, in my experience. Yes it has very good UV transmission (down to 210 nm, as I recall), but it is very prone to static buildup and as such every particle or hair in the room will cling to it. Plus it tend to scratch quite easily. Glass is cheap- get a nice big thick slab and know that once it's lived its life, you can toss it in the trash with a clear conscience.

[Eric Rose]

About as thick as Buddy Holly's glasses. :laugh:

[jermaineB]

Allo

[jp498]

Frosted or not, if it's to reduce newton rings shouldn't be a problem doing paper negatives. The paper will be the diffusion.

[Jim Noel]

I use 1/8" glass from a frame shop in all of my contact printing frames. Some have anti-glare and some don't. MY 7x17 frame made in 1946 has the original glass which is 1/8" clear and works perfectly.