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another possible factor in exposing plates

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  • Marnie Powers
    Hi all- I m new to the list, and I m unsure if this question has already been raised. Has anyone considered the validity of a single light source? I know that
    Message 1 of 11 , Jan 7, 2002
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      Hi all-

      I'm new to the list, and I'm unsure if this question has already been
      raised. Has anyone considered the validity of a single light source? I
      know that the exposure must be directly perpendicular to the plate so
      that light does not pass through the open areas of the negative at an
      angle, thus producing slabs on the sides of the relief areas verses a
      hard edge. Would a single light source such as a metal hallide lamp
      produce crisper results? That's what the printmaking stuido here at the
      University of Utah is using for polymer and screenprinting. We (at the
      letterpress shop) continue to use a multi-bulb black light blue
      flourescent unit. Works great for type and line work, but not so well
      with fine halftones. As a photographer, I've been doing a lot of
      photographic exposures with tight line screens-- a serious challenge.
      Boy do I hear you in regards to the plates headed straight to the waste
      bin. I'd be interested in anyone's thoughts on this issue.

      Marnie
      Marnie Powers-Torrey
      Studio Manager
      Book Arts Program
      J.Willard Marriott Library
      (801)585-9191
    • bielerpr
      Dear Marnie What kind of processing unit are you using? I m a bit confused by this without knowing that. Most of the industrial plate processing machines do
      Message 2 of 11 , Jan 7, 2002
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        Dear Marnie

        What kind of processing unit are you using? I'm a bit confused by
        this without knowing that.

        Most of the industrial plate processing machines do use a rack of
        lights. So while directly over the plate, light is also being brought
        in at an angle. The angle of incidence is not a factor as it would be
        with photo silkscreen, however. Usually a translucent material (virgin
        vinyl), rather than a transparent (acetate) drawn-down sheet, ensures
        proper adhesion of film negative to plate during exposure. This helps
        prevent "offsetting" from the light source.

        Exposure should not be through transparent materials because they refract
        the light. But to some extent, halation is necessary to create the proper
        shoulder. The molecular structure of the polymer changes, the strands
        lengthen and crosslink. This makes them insoluable. It does not technically
        harden them. After washout and drying, the plate again needs to be exposed
        to ensure that all the polymer has been altered. I have not encountered any
        problem processing halftones that could not be attributed to the inital
        creation of the halftone itself, it, poor contrast, improperly sharpened, etc.

        We've used high intensity photo lamps for exposing photo collotype plates
        (photo sensitive gelatin on glass) but that's a different animal entirely.
        Various photo lamps produce a quite intense and focused light. Photopolymer
        needs a standard exposure rate (as provided by the configured rack of lights)
        at a variable exposure time. For halftones you need longer exposure times,
        though if they need to be sharpened a bit you can back off for a bit "crispier"
        result. Any standard machine will process 150 line screens. though it takes
        great care to "print" them successfully with the letterpress process.

        Don't know if this is quite the response that will help you but...

        Gerald


        --- In PPLetterpress@y..., "Marnie Powers" <mpowers@l...> wrote:
        > Hi all-
        >
        > I'm new to the list, and I'm unsure if this question has already been
        > raised. Has anyone considered the validity of a single light source? I
        > know that the exposure must be directly perpendicular to the plate so
        > that light does not pass through the open areas of the negative at an
        > angle, thus producing slabs on the sides of the relief areas verses a
        > hard edge. Would a single light source such as a metal hallide lamp
        > produce crisper results? That's what the printmaking stuido here at the
        > University of Utah is using for polymer and screenprinting. We (at the
        > letterpress shop) continue to use a multi-bulb black light blue
        > flourescent unit. Works great for type and line work, but not so well
        > with fine halftones. As a photographer, I've been doing a lot of
        > photographic exposures with tight line screens-- a serious challenge.
        > Boy do I hear you in regards to the plates headed straight to the waste
        > bin. I'd be interested in anyone's thoughts on this issue.
        >
        > Marnie
        > Marnie Powers-Torrey
        > Studio Manager
        > Book Arts Program
        > J.Willard Marriott Library
        > (801)585-9191
      • Mark Attwood
        Marnie wrote: Would a single light source such as a metal hallide lamp ... Marnie, I used a metal halide 5kw unit for exposing plates for some time before I
        Message 3 of 11 , Jan 9, 2002
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          Marnie wrote:

          Would a single light source such as a metal hallide lamp
          > produce crisper results?

          Marnie,
          I used a metal halide 5kw unit for exposing plates for some time before I
          got the multiple bulb fluorescent unit that I now use. My exposure times
          were VERY long (about 20 min) despite the power of the unit. After some
          research I learned that the polymer plates use a slightly different
          frequency of UV light to the metal halide, and this is where the UV
          fluorescent tubes have their wavelength.

          my 2c worth,


          Mark Attwood

          The Artists' Press
          Box 623
          Newtown
          2113
          South Africa

          Tel. +27 11 836 5474
          fax. +27 11 836 6858
          mark@...


          ----------
          >From: "Marnie Powers" <mpowers@...>
          >To: PPLetterpress@yahoogroups.com
          >Subject: [PPLetterpress] another possible factor in exposing plates
          >Date: Mon, Jan 7, 2002, 5:13 pm
          >

          > Hi all-
          >
          > I'm new to the list, and I'm unsure if this question has already been
          > raised. Has anyone considered the validity of a single light source? I
          > know that the exposure must be directly perpendicular to the plate so
          > that light does not pass through the open areas of the negative at an
          > angle, thus producing slabs on the sides of the relief areas verses a
          > hard edge. Would a single light source such as a metal hallide lamp
          > produce crisper results? That's what the printmaking stuido here at the
          > University of Utah is using for polymer and screenprinting. We (at the
          > letterpress shop) continue to use a multi-bulb black light blue
          > flourescent unit. Works great for type and line work, but not so well
          > with fine halftones. As a photographer, I've been doing a lot of
          > photographic exposures with tight line screens-- a serious challenge.
          > Boy do I hear you in regards to the plates headed straight to the waste
          > bin. I'd be interested in anyone's thoughts on this issue.
          >
          > Marnie
          > Marnie Powers-Torrey
          > Studio Manager
          > Book Arts Program
          > J.Willard Marriott Library
          > (801)585-9191
          >
          >
          > To post a message to the membership, send an email to
          > PPLetterpress@yahoogroups.com
          >
          > To log on to the groupsite (confirmed Yahoo ID required), go to
          > http://groups.yahoogroups.com/group/PPLetterpress
          > [copious reference sources can be found onsite in Bookmarks (URLs),
          > Database (tables), Files (documents), and Messages (archives)]
          >
          > Encountering problems? send an email to
          > PPLetterpress-owner@yahoogroups.com
          >
          > To unsubscribe, send an email to
          > PPLetterpress-unsubscribe@yahoogroups.com
          >
          >
          >
          > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
          >
        • Marnie Powers
          Mark, Thanks much for the information. Do you have any details on the specific UV frequency of metal halide verses flourescent, and the ideal frequency for
          Message 4 of 11 , Jan 9, 2002
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            Mark,

            Thanks much for the information. Do you have any details on the
            specific UV frequency of metal halide verses flourescent, and the ideal
            frequency for exposing photopolymer plates? If so, I'd be interested in
            seeing it.

            Best,

            Marnie
            Marnie Powers-Torrey
            Studio Manager
            Book Arts Program
            J.Willard Marriott Library
            (801)585-9191
          • Marnie Powers
            Gerald- The information that you provided was very interesting. I m somewhat familiar with the collotype process and know photosilkcreen fairly well. I realize
            Message 5 of 11 , Jan 9, 2002
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              Gerald-

              The information that you provided was very interesting. I'm somewhat
              familiar with the collotype process and know photosilkcreen fairly
              well. I realize these are birds of a different feather.

              To respond to your query about our exposure unit: it's a handmade job
              with a powerful vacuum accompanied by the translucent vacuum film
              that Gene Becker sells. The light source is six black light blue
              flourescent bulbs. There's about an inch between the surface to be
              exposed and the bulbs. Works very well except for high resolution
              photographs. Or rather, I do very well except with high resolution
              photographs.

              How I make the negative:

              Scan a 35mm slide or negative at @1200 dpi. Especially if it's low
              contrast, I play around with the curves in photoshop, condensing? the
              values somewhat (move the two points at either end of the diagonal
              inward so that I have a "new" diagonal line that runs directly parallel
              to and above the "original" one). It seems that I loose less detail this
              way then when I change the contrast/brightness, while still acheiving
              a denser negative with a little less tonal range. I have the image output
              on imagesetting film with a stochastic screen at "80". The difficutly is
              that the stochastic screen (as I understand it anyway) does not directly
              translate to lpi. With lower resolution photos the results are excellent.
              Using a negative produced in the darkroom with a tradition halftone
              screen, the results are excellent. I'm just trying to push the process a
              bit further.

              Maybe the dot gain is just too great on the letterpess. Or maybe when
              the dots get too small, the relief in the plate is not substantial enough.
              I've been able to do very high resolution/low contrast/high detail
              work with photopolymer plates printed intaglio, that I keep wanting
              the same to be possible with letterpress.

              I'd very much appreciate your (or anyone else's) feedback on how I'm
              dealing with these chanllenges...

              Best,

              Marnie
              Marnie Powers-Torrey
              Studio Manager
              Book Arts Program
              J.Willard Marriott Library
              (801)585-9191
            • bielerpr
              Dear Marnie Here s a useful page with a lot of links re: the halftone process http://halftones.info/ For further ref this is in Bookmarks under Tech Info
              Message 6 of 11 , Jan 9, 2002
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                Dear Marnie

                Here's a useful page with a lot of links re: the halftone process

                http://halftones.info/

                For further ref this is in Bookmarks under Tech Info

                Gerald
              • Katie Harper
                ... I m unfamiliar with the term stochastic screen. Can you explain what this is? Thanks. Katie Harper
                Message 7 of 11 , Jan 9, 2002
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                  > From: "Marnie Powers" <mpowers@...>
                  > Organization: Marriott Library
                  > Reply-To: PPLetterpress@yahoogroups.com
                  > Date: Wed, 9 Jan 2002 11:29:26 -0700
                  > To: PPLetterpress@yahoogroups.com
                  > Cc: vhindley@...
                  > Subject: [PPLetterpress] Re: another possible factor in exposing plates
                  >
                  > I have the image output
                  > on imagesetting film with a stochastic screen at "80". The difficutly is
                  > that the stochastic screen (as I understand it anyway) does not directly
                  > translate to lpi.


                  I'm unfamiliar with the term "stochastic" screen. Can you explain what this
                  is? Thanks.

                  Katie Harper
                • Marnie Powers
                  Hi Katie- I m willing to explain the stochastic screen to the best of my ability. As I understand it, it is not a random screen. Under a loupe it looks very
                  Message 8 of 11 , Jan 9, 2002
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                    Hi Katie-

                    I'm willing to explain the stochastic screen to the best of my ability.
                    As I understand it, it is not a random screen. Under a loupe it looks
                    very similar to the grain of photographic film and paper. The screen
                    applies a spattered pattern to the image, the dots occurring more
                    frequently in dark areas than in the light areas. In terms of fooling the
                    eye into thinking it's seeing grayscale, stochastic is the most effective
                    screen currently availabe. Software is expensive, and I have my
                    service bureau do it. It's not used for offset prepress work however, so
                    finding a provider can be a little challenging.

                    Best,

                    Marnie

                    To: <PPLetterpress@yahoogroups.com>
                    From: Katie Harper <knharper@...>
                    Date sent: Wed, 09 Jan 2002 14:54:12 -0500
                    Subject: Re: [PPLetterpress] Re: another possible factor in exposing plates
                    Send reply to: PPLetterpress@yahoogroups.com

                    [ Double-click this line for list subscription options ]






                    > From: "Marnie Powers" <mpowers@...>
                    > Organization: Marriott Library
                    > Reply-To: PPLetterpress@yahoogroups.com
                    > Date: Wed, 9 Jan 2002 11:29:26 -0700
                    > To: PPLetterpress@yahoogroups.com
                    > Cc: vhindley@...
                    > Subject: [PPLetterpress] Re: another possible factor in exposing plates
                    >
                    > I have the image output
                    > on imagesetting film with a stochastic screen at "80". The difficutly is
                    > that the stochastic screen (as I understand it anyway) does not directly
                    > translate to lpi.


                    I'm unfamiliar with the term "stochastic" screen. Can you explain what this
                    is? Thanks.

                    Katie Harper




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                    Database (tables), Files (documents), and Messages (archives)]

                    Encountering problems? send an email to
                    PPLetterpress-owner@yahoogroups.com

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                    Marnie Powers-Torrey
                    Studio Manager
                    Book Arts Program
                    J.Willard Marriott Library
                    (801)585-9191
                  • bielerpr
                    ... Dear Marnie Have you tried ISIS Icefields (grayscale software, renders stochastic, available as a plug-in for Photoshop)? Heard great things, especially
                    Message 9 of 11 , Jan 9, 2002
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                      Marnie Powers wrote:

                      > I'm willing to explain the stochastic screen to the best of my ability.
                      > As I understand it, it is not a random screen. Under a loupe it looks
                      > very similar to the grain of photographic film and paper. The screen
                      > applies a spattered pattern to the image, the dots occurring more
                      > frequently in dark areas than in the light areas. In terms of fooling the
                      > eye into thinking it's seeing grayscale, stochastic is the most effective
                      > screen currently availabe. Software is expensive, and I have my
                      > service bureau do it. It's not used for offset prepress work however, so
                      > finding a provider can be a little challenging.

                      Dear Marnie

                      Have you tried ISIS Icefields (grayscale software, renders
                      stochastic, available as a plug-in for Photoshop)? Heard great
                      things, especially for inkjet.

                      http://www.isisimaging.com


                      Gerald
                    • Mark Attwood
                      Marnie, It was a few years ago that I did the research into the different wavelengths, and it seems I haven t filed it. The suppliers of the plates will be
                      Message 10 of 11 , Jan 10, 2002
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                        Marnie,

                        It was a few years ago that I did the research into the different
                        wavelengths, and it seems I haven't filed it. The suppliers of the plates
                        will be able to tell you the best wavelength to expose their plates, and the
                        suppliers of the bulbs will give you detailed info on the output wavelength
                        of the lamp. If I remember correctly there was only a small overlap at one
                        end of the spectrum, and this is why the metal halide will work, but only
                        with such a long exposure.

                        let me know what you find out,

                        Regards,
                        Mark.


                        Mark Attwood

                        The Artists' Press
                        Box 623
                        Newtown
                        2113
                        South Africa

                        Tel. +27 11 836 5474
                        fax. +27 11 836 6858
                        mark@...


                        ----------
                        >From: "Marnie Powers" <mpowers@...>
                        >To: PPLetterpress@yahoogroups.com
                        >Subject: [PPLetterpress] another possible factor in exposing plates
                        >Date: Wed, Jan 9, 2002, 5:56 pm
                        >

                        > Mark,
                        >
                        > Thanks much for the information. Do you have any details on the
                        > specific UV frequency of metal halide verses flourescent, and the ideal
                        > frequency for exposing photopolymer plates? If so, I'd be interested in
                        > seeing it.
                        >
                        > Best,
                        >
                        > Marnie
                        > Marnie Powers-Torrey
                        > Studio Manager
                        > Book Arts Program
                        > J.Willard Marriott Library
                        > (801)585-9191
                        >
                        >
                        > To post a message to the membership, send an email to
                        > PPLetterpress@yahoogroups.com
                        >
                        > To log on to the groupsite (confirmed Yahoo ID required), go to
                        > http://groups.yahoogroups.com/group/PPLetterpress
                        > [copious reference sources can be found onsite in Bookmarks (URLs),
                        > Database (tables), Files (documents), and Messages (archives)]
                        >
                        > Encountering problems? send an email to
                        > PPLetterpress-owner@yahoogroups.com
                        >
                        > To unsubscribe, send an email to
                        > PPLetterpress-unsubscribe@yahoogroups.com
                        >
                        >
                        >
                        > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
                        >
                      • Marnie Powers
                        Gerald I m so glad that I joined this list. I ve learned so much already! Your referrals have been extraordinarilly helpful, and the discussion is to the point
                        Message 11 of 11 , Jan 11, 2002
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                          Gerald

                          I'm so glad that I joined this list. I've learned so much already! Your
                          referrals have been extraordinarilly helpful, and the discussion is to
                          the point and interesting.

                          Best,
                          Marnie

                          To: PPLetterpress@yahoogroups.com
                          From: "bielerpr" <bieler@...>
                          Date sent: Wed, 09 Jan 2002 23:22:58 -0000
                          Subject: [PPLetterpress] Re: another possible factor in exposing plates
                          Send reply to: PPLetterpress@yahoogroups.com

                          [ Double-click this line for list subscription options ]

                          Marnie Powers wrote:

                          > I'm willing to explain the stochastic screen to the best of my ability.
                          > As I understand it, it is not a random screen. Under a loupe it looks
                          > very similar to the grain of photographic film and paper. The screen
                          > applies a spattered pattern to the image, the dots occurring more
                          > frequently in dark areas than in the light areas. In terms of fooling the
                          > eye into thinking it's seeing grayscale, stochastic is the most effective
                          > screen currently availabe. Software is expensive, and I have my
                          > service bureau do it. It's not used for offset prepress work however, so
                          > finding a provider can be a little challenging.

                          Dear Marnie

                          Have you tried ISIS Icefields (grayscale software, renders
                          stochastic, available as a plug-in for Photoshop)? Heard great
                          things, especially for inkjet.

                          http://www.isisimaging.com


                          Gerald





                          To post a message to the membership, send an email to
                          PPLetterpress@yahoogroups.com

                          To log on to the groupsite (confirmed Yahoo ID required), go to
                          http://groups.yahoogroups.com/group/PPLetterpress
                          [copious reference sources can be found onsite in Bookmarks (URLs),
                          Database (tables), Files (documents), and Messages (archives)]

                          Encountering problems? send an email to
                          PPLetterpress-owner@yahoogroups.com

                          To unsubscribe, send an email to
                          PPLetterpress-unsubscribe@yahoogroups.com



                          Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/


                          Marnie Powers-Torrey
                          Studio Manager
                          Book Arts Program
                          J.Willard Marriott Library
                          (801)585-9191
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