contact frame glass

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Leon

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I'm considering building my own large contact printing frame. I think I have the basics of the frame in hand, but is there any special consideration I need for the glass quality/ type?
 

sparx

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Most glass has to meet minimum standards of quality these days so there sholud be no real imperfections etc. I would recommend toughened though and also get the edges polished or protect them somehow with an edge bead or similar
 

bmac

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Get single strength glass. My first frame used 1/4" glass and exposures were really long with AZO, I guess it reflected too much of the UV light.
 

shinn

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There is a type of glass available called Krystal Klear and blocks out almost NO UV and is used for projectors.... Standard glass blocks out 30% or so? I think. I'm sure someone here knows.

Sorta on the expensive side I think I was quoted 90 bucks for an 11X14 piece that was 3/4 inch thick, I was going to use it for gum printing following a substrate method. I plan to get a sheet myself once I get around to either making a new frame or picking up a Vacuum frame.

Happy Days
 

Rock Poper

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When searching the jedi archives here I found this thread

I have a question tho that wasn't answered here ...

Is UV light blocked at the (2) boundaries between the air and glass due to reflection (different refractive indexes) oris it 'absorbed' by the glass material itself as the UV travels through it ? or perhaps I'm guessing a combo of the two ?

Another way of asking this>> as flat glass always will have 2 sides the question is when does the thinkness of the glass become (or cease to become) a problem ?

cheers,
nick

(off work sick with too much time on my hands)
 

Stan. L-B

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The most important thing to consider is the way the glass, of any type was made.
To obtain the correct colour rendition/tone, the glass to be used for a printing out frame needs to be lead free. Glass that has lead in it's makeup will have a greenish tinge.
It is not important how thick the glass is, and it does not have to be toughened.
 

Rock Poper

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Stan. L-B said:
The most important thing to consider is the way the glass, of any type was made.
To obtain the correct colour rendition/tone, the glass to be used for a printing out frame needs to be lead free. Glass that has lead in it's makeup will have a greenish tinge.
It is not important how thick the glass is, and it does not have to be toughened.

so its a combo ? the lead cotent absorbs in thickness and once this is removed the UV is mostly refected at the boundaries ?

I'm going to buy a large slab today (; I have to contact print large pencil drawings on at least A2 size permatrace (possibly A1) onto cyanotype and it gets pricey at those sizes so I was considering a thinner option (not so thin as to snap easily at that size tho) ...

cheers!
nick
 

Sparky

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Is "Krystal Klear" the white trash version of Water White (google it) - ? Sounds like a porn star or something. Anyway - the Water Whites, of which there are MANY variants have no green cast whatsoever and are thus not UV blockers.
 

noseoil

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I bought my glass from a local supplier of residential glass. It has a greenish tint (lead) and is 3/16" (5mm) thick. Print times are fine for azo with regular household bulbs. If you are doing 8x10 prints or smaller, this will be fine. As has been mentioned, have the edges seamed so finger cuts can't happen.

I use this thickness because it has enough weight to press the paper and film flat. Another important part is the backing. I bought neoprene gasket material from an industrial supplier as it will act to compress the sandwich better than a hard surface. I made a compression frame, but don't use it unless it is a finished print, the weighted method works very well.

I use a small timer for azo and will always use firm hand pressure on a black paper mask to make sure there is sufficient contact before turning on the light. Azo is a single weight paper, for thick stuff which is curled, you may need a pressure or vacuum frame. tim
 

Calamity Jane

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When I was designing a water purification system using UV-C light (ultra-short wavelength), I found that all silica glass allows only about 3% of the UV-C to pass thru. Sorry I don't remember the numbers for UV-A and UV-B but I do remember that they weren't much better.

(Had to go to a quartz glass for UV-C at almost 50 times the price of common glass! EEEGADS!)
 

Rock Poper

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I bought just yer standard glass yestersay to test... a little 250x300 piece (8x10 with room to spare) - the only other type of glass they had on offer aside from the standard variety were UV blocking type glass and a ~10 times expensive 'X-Ray' glass for x-ray machines ...
 

Sparky

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Here is a general link for the glass type I was discussing... http://www.waterwhiteglass.com/

I would like to recommend corning O211 for any azo-type contact printing. You might find your exposure times dropping to about a TENTH or less of what they were, depending on the iron content of the glass you were previously using. Normal clear float glass tends to block about 90% of UV range light.

Check out the transmittance graph..!!!
http://www.eriesci.com/custom/Cor0211-curveT.aspx
 
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