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9474Re: [PPLetterpress] Re: platemaking issues

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  • Cody L
    Mar 7, 2008
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      First of all thanks for the information and your
      personal tests of the polymer and what it is doing for
      you. I did not think to stop the washout before you
      get to the clear base. I was just trying to match the
      materials purchased from Boxcar on previous plate

      I also appreciate the quick run down on light and
      plate interaction. Yes the book in question is on its
      way from a friend but it is not here now. I thank you
      all for your patience!

      With a hand washout i will probably have to be careful
      with uniformity of the depth washed out and make sure
      they properly dry before the hardening process.

      If I were to create my own conversion to florescent UV
      bulbs what should I look for. I have never searched
      for the bulbs before just the entire platemaker. I
      don't see that it would be very difficult to
      accomplish a custom box that could sit on top of my
      vacuum unit and have it hooked to a darkroom timer. I
      have found bulbs online but I do not know if a UVA
      tanning style bulg is what is required or a UV black
      light bulb would be the correct style.



      --- Peter Fraterdeus <peterf@...> wrote:

      > Hi Cody, et alia
      > Richard wrote:
      > > The characteristic
      > > slope of a well made photopolymer plate is the
      > result of how
      > > photopolymer bends the light ray at the point it
      > enters the
      > > photopolymer.
      > Photons do travel in a straight line, and thus a
      > broad light source
      > will create a light cone, regardless of diffraction.
      > Your argument implies that the source is an
      > infinitely distant point.
      > While the ray may bend due to the change in medium,
      > I don't think
      > that's the reason for the slope of the shoulder.
      > As far as it goes, I am finding that the plate
      > material from Boxcar
      > produces very vertical shoulders. I think this is as
      > much due to the
      > fact that the yellow color absorbs the UV, and
      > therefore the photons
      > coming at an angle do not spread much beyond the
      > point of entry. Those
      > which enter at a shallow angle are absorbed before
      > reaching the base.
      > It seems to me that the shoulder angle is related to
      > the photo-
      > sensitivity of the polymer.
      > I've been trying to find more in-depth technical
      > info on all this,
      > rather than apocryphal say-so, but the
      > manufacturer's documentation
      > (what little there is) seems to have been translated
      > from Japanese
      > into English leaving much to the imagination.
      > Perhaps I'm looking up
      > the wrong trees. Google likewise provides little
      > elucidation. Of
      > course there's Gerald's book, but why not reinvent
      > the wheel every
      > generation? Also, the plate materials seem to have
      > changed since the
      > copy I have was published.
      > The problems I was having previously with loss of
      > points and moving on
      > the base had to do with too long wash-out, which
      > would undermine the
      > exposed points.
      > I'm now using about 3.5 minute wash instead of five,
      > which has done
      > wonders for the stability of the fine points and
      > rules. With the 'deep-
      > relief' base it needs another minute or so to clean
      > the base, but I'm
      > washing as short a time as possible.
      > Leaders and isolated dots and periods are solid
      > cylinders. Not much
      > shoulder, but they're hard as rocks, firmly seated
      > on the base and
      > seem to be printing fine. In fact, the older plate
      > material I was
      > using produced a wide shallow shoulder, the current
      > stuff, with the
      > clear untinted plastic base produces a nearly
      > vertical shoulder.
      > YMMV, of course....
      > Peter Fraterdeus
      > http://ExquisiteLetterpress.com
      > http://dubuquebookarts.com
      > On 7 Mar 2008, at 10:07 AM, richard seibert wrote:
      > > All light, even after being diffused, travels in a
      > straight line.
      > > When light travels out of one substance into
      > another, its speed
      > > changes. This changes the angle at which the ray
      > travels. Think of a
      > > pencil in a glass of water. Every substance has an
      > "index of
      > > refraction" which determines what this angel is.
      > The characteristic
      > > slope of a well made photopolymer plate is the
      > result of how
      > > photopolymer bends the light ray at the point it
      > enters the
      > > photopolymer. This is also why film needs to be
      > emulsion down.
      > > Nothing that happens to the light in-between being
      > emitted by the
      > > electrons in the lamp and entering the film will
      > effect what happens
      > > at the boundary between film and polymer. (Unless
      > the intervening
      > > substance absorbs or reflects the necessary
      > frequencies.)
      > >
      > > Too steep an angle is the result of not enough
      > photons (or not enough
      > > photons of the right frequency) to fully
      > polymerize the material.
      > >

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