Re: Here is why my UV print exposures were so erratic...

  I am using a Nuarc N750 plate burner that I picked up on Ebay for making kallitypes. Here's a picture of the unit: http://www.graphicassoc.com/Item_Pages/NuArc750.htm

  It has a pull-out vacuum frame drawer with a 17x22 inch bed, and the 1,000 watt mercury vapor light is totally encased inside the unit, whch is actually quite nice. There is also a vacuum pump and a cooling fan on the back of the unit. It is powered by a standard 120V outlet, 20 amps.

  Normally the N750 has a built in integrator that measures the amount of UV light like a timer. Mine was working erratically and wasn't reliable, probably due to old age. I picked up a stand-alone Olec integrator and the probe that goes inside the unit.

  The last N750 on Ebay went for a pittance....$75 or something. They are older models and quite forgotton, but just as effective as a Nuark 26-1k which also sports a 1,000W mercury vapor lamp. But they do weigh over 150 lbs., so shipping is a factor.

  The mercury vapor lamps output sharply at about 350nm which is in the UV A band. The newer Nuarc 26-1kS has a 1,000W metal halide lamp, which has a broader output band that strongly outputs over 400nm. From what I've read this should boost contrast in the prints slightly. For a primer, there is a good article on UV light sources on unblinkingeye.com

  Good luck!

  Michael

    ----- Original Message -----
    From: Leonard Peterson
    To: mklemmer@comcast.net
    Sent: Friday, January 23, 2004 11:16 PM
    Subject: RE: Here is why my UV print exposures were so erratic...

    Hi Mike, Could you please fill me in on the details on your mercury vapor lamp. I have thought this would be the way to go but there are so many different kinds. Thanks, Len

    P.S. Don't be afraid of speaking too simply to me. Any and all info will be greatly appreciated!! I really am a rank beginner in alt photo.

>From: Mike Klemmer
>Reply-To: alt-photo-process-l@sask.usask.ca
>To: alt-photo-process-l@usask.ca
>Subject: Here is why my UV print exposures were so erratic...
>Date: Fri, 23 Jan 2004 22:03:47 -0700
>
>For the longest time I could never figure out why my kallitype exposures were so erratic from print to print. Sometimes too dark... sometimes too light. I came up with every possible explanation under the sun, but tonight I finally figured it out...the real reason.
>
>What I was doing was allow the mercury vapor UV lamp to fully warm for 5+ minutes while covering up the print in the vacuum frame with heavy stock cotton paper. Well it turns out that the paper I was covering it with is not UV opaque! It was getting significant exposure before the exposure.
>
>So I finally figured it out quite by accident and thought I would share. Fortunately, now I have a working integrator so I won't have to warm up the lamp and time my exposures.
>

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Received on Sat Jan 24 09:01:17 2004