Glass for contact printer

glbeas

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• Jun 11, 2020

• #1

Im considering building a 16 x 20 contact frame, my exposure unit is big enough, and would like to know if theres any particular type of glass I should avoid due to uv absorption. How thick can regular glass be and not be a problem?

 

RalphLambrecht

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• Jun 11, 2020

• #2

glbeas said:

Im considering building a 16 x 20 contact frame, my exposure unit is big enough, and would like to know if theres any particular type of glass I should avoid due to uv absorption. How thick can regular glass be and not be a problem?

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1/8" or 3mm would work fine.

 

mshchem

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• Jun 12, 2020

• #3

I would go visit a place that sells glass. Get a good quality plate glass with the edges treated. Glass absorbs UV, especially short wave UV, but a high intensity source, or the Sun will blow right through. Auto glass is formulated to reduce UV transmission, and it does. A glass guy will know what's best. Tell them what you are trying to do. Quartz is Silicon dioxide, which is used for UV transmission. Glass is mostly SiO2. Talk to a glass guy. MHOFWIW.

 

koraks

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• Jun 12, 2020

• #4

I use 5mm hardened glass in my contact frame. Hardened glass only due to safety considerations; I'd rather not have huge shards of heavy glass in case anything breaks. The glass I use is the generic stuff (float glass) that's e.g. also used in interior applications such as glass tabel tops. No problems with UV blockage, at least not to the extent that it's an issue.

 

awty

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• Jun 12, 2020

• #5

Thats a big print.
My biggest is 14x17.
I use 5mm glass from the local glazier.
You want glass that won't flex as others have mentioned.

 

OP

OP

glbeas

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• Jun 12, 2020

• #6

Thats all good to know. The largest digital negative I can make now is 13x19 so a 16x20 would be a good match.

 

Alan9940

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• Jun 12, 2020

• #7

All of my contact printing frames use common window glass found in any Home Depot.

 

ChristopherCoy

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• Jun 12, 2020

• #8

Alan9940 said:

All of my contact printing frames use common window glass found in any Home Depot.

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Mine as well.

 

138S

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• Jun 12, 2020

• #9

glbeas said:

How thick can regular glass be and not be a problem?

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Too thick is not a problem, I use a 8mm thick one because its weight ensures enough pressure without a frame.

Rather building a frame (for convenience) you may glue two handles on a 8mm glass, then you just place a thin foam on the table, the paper, the film... and you just place the 8mm glass on all that. If you have an enlarger you mount all that on the easel...

Today glass flatness is very good in general, but you may check if your glass is of certicied flatness. I the past glass made for mirrors was of superior flatness.

 

koraks

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• Oct 12, 2020

• #10

@138S save yourself the trouble, that was just a spam message. Obviously it had absolutely nothing to do with the topic at hand. I've already reported the post.

 

Deleted member 88956

• Oct 12, 2020

• #11

koraks said:

@138S save yourself the trouble, that was just a spam message. Obviously it had absolutely nothing to do with the topic at hand. I've already reported the post.

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name suggests Jonathan Lewis the 536th is behind it, the truth is it is Jona Than Lewis on and off 536 times

 

138S

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• Oct 12, 2020

• #12

koraks said:

@138S save yourself the trouble, that was just a spam message. Obviously it had absolutely nothing to do with the topic at hand. I've already reported the post.

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ok, thanks, I had not seen in it...

 

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glbeas

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• Oct 12, 2020

• #13

For an update I salvaged an old platemaking frame and attached a vacuum pump to it. Works quite well and solved all my problems.

 

wyofilm

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• Oct 12, 2020

• #14

Ctein recommends a particular glass. Does anyone remember what the glass is? I think it was Veriglass - or something close to that.

 

138S

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• Oct 13, 2020

• #15

wyofilm said:

Ctein recommends a particular glass. Does anyone remember what the glass is? I think it was Veriglass - or something close to that.

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Post Exposure has been made free to donwload http://ctein.com/PostExposure2ndIllustrated.pdf, see Page 133.

He recommends: "Replace the ordinary glass in your contact frame or glass-negative carrier with Denglas" anti-refection coated, but expensive. This was to avoid newton rings...

Today we have cheaper anti-refective choices like True-Vue (https://tru-vue.com/solution/museum-glass/). Anyway IMO this is not much necessary if we provide a good adaptation of the negative to the glass with a proper foam in the back, providing a good contact without separations.