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9481Re: [PPLetterpress] Re: platemaking issues

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  • typetom@aol.com
    Mar 10, 2008
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      Hi Cody,
      If you use a glass top vacuum frame, you need to add matboard around the
      plate material within the frame, to support the glass across the whole surface.
      Otherwise, glass will bend under the vacuum, and allow some light to bleed
      irregularly around edges of the negative (which is not held in tight contact due
      to the bend in the glass). Without the matboard support, the plate will have
      swollen lines that print irregularly bold.

      Depending on humidity in your area, a hand-held hair dryer may be adequate
      for drying the plates. In Denver it only takes a couple of minutes. I shake the
      surface water off the plate, use lung power to blow any further moisture off
      the fine lines of the plate, and then use a small hand held dryer until the
      steel backing is about too hot to handle. Insufficient drying will result in
      a plate that continues to dry as it ages, which can result in severe curling.
      (Some degree of this is likely anyhow, but can be minimized by sufficient
      drying before the second exposure).

      Good contact with the negative, precise timing for exposure, and carefully
      limited time in the washout, are the most critical factors. I have not found
      the Stoeffer scale as useful as others attest, but recommend trial and error
      and practice, with careful observation. The various polymer materials
      available, variations of density in the negatives, variations of intensity of
      different light sources (which may be set up at different distances in a homemade
      system), all will affect the best exposure time for you to use. Different kinds
      of lines, fine details, dots that need more support, reverse lines that may
      fill in when exposed normally, all may require slightly different exposure
      times. Experience and careful observation are necessary whether you are looking
      at the results of a calibrated Stoeffer test or actual results on the job.

      A few other notes:
      Hand washout is limited by the size of brush you can handle, which affects
      how long a large plate has to be kept in the water as it is being washed. Since
      the polymer material is hardened by exposure from the surface down to the
      base, surface details will separate from the base if the plate is allowed to
      stay in the water too long. Limiting washout to under 4 or 5 minutes, I rarely
      have broken or wavy lines or missing serifs. But that means I have to stop
      washout of larger plates before they are completely clean. Not as pretty a
      finished plate, but usually not a problem on the press. Most of the plates I
      make are card/invitation size, maybe 5x7 max, though occasionally I have done an
      8x10 or larger -- I'm limited by the size of my sink as well!

      My light source is a box of 4 UV fluorescent tubes, sitting about an inch
      and a half above the glass of the vacuum frame. Cost me about $50 for the
      bulbs, everything else was free scrap stuff except the cost of the brush and a
      Stoeffer scale that I don't use. Steel backed Miraclon plates from Gene Becker
      in NYC cost about $300 for 10 large sheets. Very lucky to find a good cutter
      with leverage to cut the steel plates. Patmag aluminum backing blocks from NA
      Graphics, with a little masking tape on the edges of the plates anyhow to
      make sure nothing moves during printing. Most jobs are done on my 10x15 C&P,
      more difficulty keeping registration with the Vandercook SP15. If I were
      starting new, I'd probably go with the Boxcar system, particularly because of the
      difficulty of cutting the steel backed material and the expense of magnetic
      backing blocks which still need to be taped and watched for registration
      problems anyhow.

      No direct experience with washout of the polyester backed material, nor with
      other light sources.

      Most of my photopolymer work has been custom commercial job printing,
      hundreds of jobs, probably a dozen years since I started making plates myself (26
      years since I started letterpress). I still use handset type for most of my
      poetry projects and for jobs when it can be done. The main reasons for using
      polymer plates are 1) client familiarity with computer fonts they like; 2)
      flexibility in design work that can be done with scanned images, calligraphy,
      clip-art, and manipulation or adjustments that can be done with proofs of
      limited or worn metal type and cuts; 3) the strength of polymer plates compared
      with lead type, when printing on paper that has sticks and flowers etc, and when
      trying to please clients who want sculpture as much as readable text.

      I love it all. Best wishes,
      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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