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Re: platemaking issues

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  • parallel_imp
    ... Tom, here s another way to look at the problem of photopolymer plates in a glass-faced vacuum frame. Many photopolymer plates are smooth and tacky, and
    Message 1 of 22 , Mar 12, 2008
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      --- In PPLetterpress@yahoogroups.com, typetom@... wrote:
      >
      > . . .
      > The answer is that the glass was bending in my vacuum frame, allowing
      > some slight distortion of contact with the negative and thus an
      > irregular exposure and thus swelling in the plate. Mat board placed
      > around the plate materialwithin the frame completely solved the
      > problem. The mat board gives support forthe glass across the size
      > of the frame.

      Tom, here's another way to look at the problem of photopolymer plates
      in a glass-faced vacuum frame. Many photopolymer plates are smooth and
      tacky, and stick easily to smooth-surfaced films. If the drawdown in
      the frame is fast, a bond can form at one or more edges of the plates
      before the air is drawn out of the interior of the plate, causing
      out-of-contact bubbles. The rubber blanket pulling the plate up might
      also apply more pressure at the edges. Using the bleed valve allows
      for a soft contact, removing more air before hard contact is achieved.
      Your cardboard is definitely relieving the pressure at the edge, and
      would also be allowing more air to escape. But I think the forces at
      work are moving upward to the glass, not downward to the plate.
      The problem of plate tackiness is addressed in many manufacturer's
      instructions, specifying matte-emulsion film, or detacking powder
      (silicon spray is another possibility). I'm now using the Rigilon HX
      which itself has a matte-emulsion for better drawdown to any kind of
      film. This isn't an issue with a crene-covered frame, since you can
      brayer or burnish out any air bubbles, but with glass it is definitely
      a problem to overcome, with various possible solutions.
      --Eric Holub, SF
    • typetom@aol.com
      Something new (something old & new) every day. Thanks, Eric. My nuArc vacuum frame has a name plate but no model number, no bleed valve, but a pressure gauge
      Message 2 of 22 , Mar 12, 2008
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        Something new (something old & new) every day. Thanks, Eric.

        My nuArc vacuum frame has a name plate but no model number, no bleed valve,
        but a pressure gauge on the line. It has a glass top hinged within a metal
        frame, with a vacuum area about 21.5 x 25.5. Not clear whether it ever had a
        light attached -- it appears to have been part of a larger apparatus. The
        vacuum space below the glass is sufficient to handle plate material, more than a
        just contact prints.

        Meanwhile, I do dust the plate material with powder to prevent it from
        grabbing the negative. I don't think air bubbles are the cause of the exposure
        irregularities I experienced. Uneven pressure on the plate and negative at the
        edges of the plate (which I have assumed involves some slight bending of the
        glass) seems the likely explanation. Mat board around the plate seems to solve
        the problem completely. Whatever works!

        Thanks,
        Tom

        Tom Parson
        Now It's Up To You Publications
        157 S. Logan, Denver CO 80209
        (303) 777-8951 home
        (720) 480-5358 cell phone
        http://members.aol.com/typetom



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