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13733Re: [PPLetterpress] Trouble with newly made exposure unit

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  • Silber MaiKätzchen
    Feb 3, 2014
    • 0 Attachment
      Use a greenhouse plastic sheet from a garden shop, these are designed to pass UV
      wavelengths. Acrylic filters UV out and reflects it back to the light source.

      Put a black surface under the plate, I recommend a low durometer lightly textured
      black elastometer or a matte black opaque polycarbonate. Hard or soft is a personal
      choice. I prefer flexible to hard for the back and glass next to the light source.
      Actually I would recommend buying a ready made exposure blanket from a company
      like Douthitt and a 1/4" glass to contact against. This will require a vacuum pump.

      http://www.douthittcorp.com/Catalog/catalog.htm  (See P. 34)

       
      MaiKätzchen

      Dum loquimur, fugerit invida Aetas:
      Carpe diem!
      quam minimum credula postero!

      Horace
      Odes Book I



      From: Michael Hurley <mephit@...>
      To: PPLetterpress@yahoogroups.com
      Sent: Monday, February 3, 2014 2:42 PM
      Subject: Re: [PPLetterpress] Trouble with newly made exposure unit

      On Feb 3, 2014, at 1:15 PM, Peter Nevins <nevins.peter@...> wrote:

      > white reflective surface below film and plates is gonna be a problem:  stray light bouncing around is bound to blur the image.
      > without a vacuum, it's only possible to achieve uniform pressure by placing the lights below the glass and weighting the film and plate down onto the glass image from the top.  it's simply not possible to tape the image down in a way that keeps it flat to expose from above.
      > you could (?) weigh down a piece of glass to press the plate and film together from the top, but it won't be as effective.
      > 1 inch is too close to provide evenly diffused light:  you're bound to get bands of more and less exposure.
      > ok there, I'm done

      I don’t have any direct experience with platemaking, but I have looked into building an exposure unit before. According to my research, the acrylic could be the problem. Acrylics are almost always very reflective to UV, unless specifically stated to be otherwise. This is a standard treatment given to acrylics (especially things like Lexan) to keep them from getting milky-colored as quickly when used as windows. Even the specialty acrylics that don’t have the anti-UV additives aren’t nearly as UV-transmissive as glass. Anyone have any direct experience with this?
      --
      Michael Hurley                  Titivilus Press
      123 North Holmes St.  titiviluspress@...
      Memphis, TN 38111                (901) 831-7640



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