Contact/UV printing Question

Discussion in 'Alternative Processes' started by photomem, Oct 10, 2009.

  1. photomem

    photomem Member

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    I am wondering if there is any correlation between the UV ratings put out by the Weather Service each day and the exposure time when contact printing using the sun.
     
  2. Vaughn

    Vaughn Subscriber

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    Should be some correlation. Probably based on one's latitude, season (angle of rays), ozone concentration, altitude, and maybe humidity. Index is based on a cloudless day at noon.

    If one were to make a series of exposures and keep track of the forecasted UV index, one might be able to make a correction chart of some use.

    I tend to print at night, but since the amount of UV reflected by the moon is low, I use artificial UV sources:wink:

    Vaughn
     
  3. PVia

    PVia Member

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    Actually, I print by the sun exclusively in pt/pd and recently gum dichromate. I've kept a log over the last 1 1/2 years with time of day, temperature, relative humidity and UV Index for each print and test strip I've made. The local UV Index can be found at wunderground.com; just type in your zip code and choose a location closest to you.

    I have the advantage of living in So Cal, with perfectly clear cloudless skies on a majority of days throughout the year. I've found that from UV 4 to about UV 11, my pt/pd printing time remains the same.

    If it gets hazy or cloudy, all bets are off. For example, during the recent forest fires here I tried to make a few exposures. Although it wasn't smoky in the air near my house, the smoke/haze that hung in the atmosphere definitely affected my exposure times.
     
  4. Curt

    Curt Subscriber

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    Does smog or the smog index there affect the exposures? When I lived in Glendale it was smoggy a lot.
     
  5. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    Since you mention in another thread that you're albumen printing, one advantage of that process is that you can inspect the print as you go, presuming you have a split back print frame. The print should look about two stops darker than you want it to be, since it will bleach out somewhat in the toner and fixer. The unexposed film rebate area on the print should have a metallic sheen.

    My best negs for albumen usually have around a 20 minute exposure time in direct sun, 1 hour in indirect sun.
     
  6. PVia

    PVia Member

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    First off, smog, while still present in the LA basin, is way down from the levels many years ago. I live in Pasadena, which used to be known as the worst place for smog, however one can easily see clear detail in the San Gabriel Mountains almost every day of the year.

    I never find that smog levels interfere with exposures. As I mentioned, the only thing that hinders exposures are clouds and smoke from fires.

    However, today it is raining (the first rain in 9-10 months!!!) and there will be no exposures :sad:

    This is probably one of the few places in the country where you can rely on the sun to print exactly the same btw the hours of 10:30am - 3:30pm almost every day, ok, maybe 330 days a year.

    If I did this commercially, I'd get a plate burner in a sec...