Is there a special glass used for contact printing?

Discussion in 'Contact Printing' started by foton33, May 26, 2007.

  1. foton33

    foton33 Member

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    Is it ok to use regular glass to make 8x10 contact prints in a contact print frame? I have been having some problems with newton rings(?). Those sort of rainbow rings that come up in the print sometimes. Any advice on how to get rid of those things? Is it a flaw in the glass that causes it?
     
  2. Gary Holliday

    Gary Holliday Member

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    The only advice really is to have everything clean and dust-free as possible.
     
  3. Monophoto

    Monophoto Member

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    Ordinary glass is fine.

    Newton's rings are an interference pattern created when the contact between the negative and glass isn't perfect. The problem can be avoided by using special glass, by adding a fine powder between the glass and the negative (although that's probably not a great idea if you are making contact prints), or by making sure that the glass applies uniform pressure across the 8x10 print surface. The latter is the most common solution, and either involves using glass that is thick enough that the weight of the glass completely flattens the negative, or by using a contact printer with back springs to flatten the sandwich of glass, negative and printing paper.
     
  4. Curt

    Curt Subscriber

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    Against professional advise I bought a sheet of "Optical Glass" which came with a certificate and number. I paid $80.00 so it wasn't cheap. I have not had a problem since I started using it. It's thicker than window glass and is a really a nice work in its own right.

    Curt
     
  5. foton33

    foton33 Member

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    thanks all, Jody
     
  6. Scott Peters

    Scott Peters Member

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    I use glass from ace hardware with no problems whatsoever....cheap too. Regular window glass.
     
  7. dancqu

    dancqu Member

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    I'll add to the OP's question. How about coated framing glass.
    A frame shop informed me that they can frame using non-reflective
    glass. I've thoughts it may also be good for a projection printing
    frame. I've some really bent enlarging paper. Dan
     
  8. Nick Zentena

    Nick Zentena Member

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    I use plate glass for contacts without a contact frame.

    For enlarging? Isn't that going to be like sticking a new element on the enlarger lens?
     
  9. dancqu

    dancqu Member

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    An interesting point. A flat over a lens is not thought
    of as altering the optics; filters front or rear. Do to the
    intimate contact with the paper I doubt there would be
    any problem. Interference patterns? Dan
     
  10. Nick Zentena

    Nick Zentena Member

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    Filters do shift focus. It may not be much. It can be very little for a very thin gel filter but to the best of my knowledge they do shift the focus. The Kiev fisheye lenses require a filter to be used. It's part of the optical design.
     
  11. juan

    juan Subscriber

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    I use plate glass in my contact printer with no problems. In my scanner, I use two sheets of non-glare picture frame glass from the framing shop. I put the dull side towards the negative on both top and bottom. Cost for two sheets of glass cut 8x10 with buffed edges was about $10. If you're having Newton's ring problems, a sheet of this glass might help. It's certainly cheap enough to try.
    juan
     
  12. bdial

    bdial Subscriber

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    Anytime light moves from one medium, such as air, to another, such as glass, it refracts. In theory, when the glass surfaces are parallel the shift is back to the original path. My concern in putting glass over the paper for enlarging would be whether the glass surfaces are perfectly parallel, or how imperfect they might be, and whether the surfaces are in perfect alignment with the lens, which almost certainly, they will not be.
    Whether those imperfections are enough to matter for your eyes is a different issue.
     
  13. dancqu

    dancqu Member

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    So you sandwich the negative between two sheets of glare
    free glass, both dull sides in contact with the negative. Dull
    sides sound bad. Dull yet clear? That glass will need a look.
    I'd be laying a glass sheet upon the enlarging paper. Dan
     
  14. Steve Sherman

    Steve Sherman Subscriber

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    I used to use a piece of plae glas
     
  15. Steve Sherman

    Steve Sherman Subscriber

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    The previous post didn't work out to well.

    I used to use a piece of 1/4" plate glass with not frame. In using Azo I found the printing time quite long. Just happened to switch to a vacuum frame which uses a piece of clear 1/8" glass, the printing times were significantly shorter with the same negatives. I asked a glass person why and he said that plate glass is inherently stronger than ordinary glass and actually has a light reducing effect, he simply asked if the sides of the glass were at all green, that is an indication of "plate" glass which reduces light transmission.

    Cheers!
     
  16. Jim Noel

    Jim Noel Member

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    I use "Non-Glare" glass from picture frames. I have no problem with Newton Rings, and the texture does not effect the sharpness of the image. It is thin and therefore gives me fast printing times.
     
  17. dslater

    dslater Subscriber

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    Also, Azo is largely sensitive to UV and glass tends to block UV - that's why UV lenses are made of quartz. I'd bet that if you were using ordinary enlarging paper, you wouldn't see nearly as much difference between the 2 pieces of glass.

    Dan
     
  18. z-man

    z-man Member

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    glass is not the whole issue

    humidity causes the geletine to swell more than the backing thus the increase in newtons rings in high humidity due to the decrease in flatness in the film and the resulting irregularity in contact with glass

    solutions in regular use for at least 100+ years that will work:

    use thicker glass-it weighs more and is stiffer so you get better contact between glass and neg/pos/whatever

    use nonglare picture framers glass with texture against film

    dust with offset powder-cornstarch

    use a vacuum easel without glass

    strip neg and/or pos into support flat with or without window-this will make film lie flatter

    experiment with emulsion up/down in combination and against glass

    use film with retouching surface on on one or both sides

    fyi: glass blocks uv, float and plate glass contains iron that turns glass cyan and blocks more uv-whaterver is a poor alt process artist to do????--duh --use plastic

    fyi: glass both "water white", window glass, nonglare or whatever has been and still is in use daily for 100+ years in all things photgraphic to produce everything you see in print and on the packageing of everything you buy-yes a gel(itine)filter is optically better than any glass but so what-yes an optical flat is more parallel than window glass but so what-yes a vacuum easel or frame will pull material flat but so what

    without skill, technique, craft and knowledge gained by working smarter-not harder-or worse yet, by instead throwing money at a problem all you get is is foolishness-and crafty venders richer and fatter

    vaya con dios