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599RE: [PPLetterpress] Aging plates?

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  • Joel Benson
    May 14, 2002
    • 0 Attachment
      Hi Ed,

      Sorry for the slow reply here- yes, they are called "Blacklights" on the bulbs, but they aren't purple-looking like the incandescent blacklights. They cost me about $15 each, I think. I'll look at the product numbers when I get home- though I think it is a pretty standard Phillips bulb. I use about a 4 minute exposure time for fine type, 30 to 45 seconds for big solids or halftone screens.

      I don't think it is the wattage that makes the difference so much as the specific wavelength of UV that the bulb gives off. I think the lamps you are using probably emit a large amount of light at one end of the UV spectrum and a lesser amount at the other end, which happens to be the end that the polymer is sensitive to. I remember a discussion of this with details about the wavelengths on either this list or LETPRESS, but I don't have it saved anywhere.

      It sounds like there is a lot of leeway in exactly how far the bulbs need to be from the plate material. Silver May Kitten has the bulbs a foot away, Brian Allen has his 1.5-2" away and much closer together. That seems to define a range of acceptability. Using a Stouffer scale would tell you how long your exposure needs to be for whatever set up you construct.

      Joel

      Joel Benson
      Dependable Letterpress
      San Francisco

      -----Original Message-----
      From: Ed Inman [mailto:edinman@...]
      Sent: Monday, May 13, 2002 5:15 PM
      To: PPLetterpress@yahoogroups.com
      Subject: Re: [PPLetterpress] Aging plates?


      You expose polymer with 40 Watt lamps? What exposure times do you use with
      this setup, Joel? Are you referring to regular purple looking
      "blacklights?" I didn't think such a low wattage setup would work very well
      even with hours of exposure. Can you give us a product descritption as
      printed on the bulbs you use and a little more detail as to your process?

      For what it's worth my cheapo homemade lamp setup is just a Sylvania "Sun
      Gun" that uses a 650 watt "DWY" halogen photo optic lamp. The lamps come
      with a warning that the bulb emits UV radiation and that you should not look
      directly into the fixture. You can usually find these used on ebay for $10
      to $15 and they will expose polymer very nicely in about 30 minutes time
      from about four feet back. I think both the original Sylvania Sun Gun and
      the Sun Gun 2 both use the same DWY lamp.

      Ed

      Joel wrote:
      >>> The UV bulbs can go into standard flourescent fixtures. The unit I have
      has four standard, 24", straight-from-the-hardware-store, two-bulb fixtures
      mounted in it and wired up so they all come on together. I think the bulbs
      are 40W.<<<




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