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  1. #11

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    Nope it's a 300W UV lamp which didn't move a millimeter between the prints I let it pre-heat to only begin exposure when it is at full power. I guess I'll have to get a humidifier / dehumidifier.

  2. #12

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    I live in Houston, Texas. It is very humid here. I'm making prints now, and I'll be interested to know what happens when I make the same prints in the wintertime. I'll keep you updated if things change with the humidity levels.
    Good luck!
    Steve
    www.scdowellphoto.com

  3. #13

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    Thanks Steve, more data is always useful, although the humidity/exposure relationship is established beyond doubt, not just with my tests. In laboratory studies where the temperature was held constant and the humidity varied, the relationship is almost vertical. This is borne out by the nice chart Loris linked, put together with my experience: when I was living at the beach, the most common environmental condition (I printed in a studio with the windows wide open, winter and summer, so the outside climate was the same as the inside climate) year around was around 50-55 F and 85-90% humidity. According to this chart, that's around 10% absolute humidity. My routine exposures in those conditions were 2-3 minutes. On an unusually dry day when the humidity plunged to 17% and the temperature was in the low 70s (somewhere around 4% absolute humidity) my exposures zoomed to 20+ minutes. In other words a 6% change in absolute humidity can generate a 10x change in exposure. As generations of gum printers have demonstrated, you can print gum without a humidifier or dehumidifier, or without climate-controlled conditions, but you do need to be aware in changing conditions to vary your exposures accordingly.
    Katharine

  4. #14

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    Hmm very intreresting indeed, then we would just need to find a formula close enough to the experienced change in exposure times so we could calculate this. Because if 6% is 10 times, is 3% 5 times or is there another type of progression ?... Here from what I gathered from the weather reports archives, the humidity dropped from 12% absolute to 5% absolute, so about 7% too in fact ...

  5. #15

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    Hmm... With gum I would never give an observation as a rule.. I was just sharing that informal observation in support of the established observation that says "less humidity = more exposure" and that the relationship is a steep one; that's absolutely as specific as I'd go. I would never say "6% is 10x" as a rule, on the basis of an informal observation. I guess my point was that if you go by the relative humidity, it seems sort of reasonable that if you go from 90% humidity to 17% humidity it's going to make a big difference in the exposure, but when you see that that's really only a 5-6% difference in absolute humidity, it brings home the fact that the relationship between humidity and exposure is indeed a strong one.

    You're going to need to do step tablets to determine the exposure anyway; just rely on what the step tablet tells you and print gum, would be my advice. Keep track of your observations and over time, we add to the database of observations. If we ever eventually developed a humidity-exposure formula that proved universal, that would be great, but I'm not holding my breath since that's never happened for any other gum law that people have tried to establish (except for the most general, which is why I try to stick with general principles that I know are universal). Um (looking down) I see I'm standing on a soapbox, I'll get down now.
    Katharine
    Last edited by Katharine Thayer; 09-16-2009 at 10:38 AM. Click to view previous post history. Reason: remove extra word

  6. #16

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    Gum and Humidity

    I agree about establishing rules for gum that will apply universally.

    I have a "rule of thumb" I use in my setting and I am getting some nice preliminary results within a range of fluctuation of about 20%.

    However when the dry winds start here and the humidity plunges from about 60% to about 15% I will not be surprised to see my "rule" overturned.

    That seems to be the way with gum.

  7. #17

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    P.S. Anyone interested in gum printing, particularly tricolor gum, should have a look at Jon's print "Santa Margarita 1" that's currently on the main page at hybridphoto. That's gum printing:

    http://www.hybridphoto.com/gallery/showimage.php?i=602

  8. #18

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    Thanks for sharing that. It's nice indeed. OTOH, it's more like your kind of gum printing (high-keyish w/ smooth tones and pastel colors)

  9. #19

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    Well, of course, that's what I like landscape photos to look like, a natural expression of a natural scene, without any surreal boosting of saturation or contrast. I took up gum because I found the color in most color photography to be much too saturated for my taste, and I wanted a way to print a more subtle and personally pleasing image. It took me a while to learn how to print gum to look that way; I had to back way off on the pigments and choose less saturated colors to get it right. But yes, I think this is a beautiful gum print, and yes, it's how I like color pictures, especially of natural scenes, to look. I don't suppose that's surprising. I like to be able to look at a color picture and enjoy it and take it in instead of having my eyes assaulted by unreal color or contrast.

    (I also hated Ansel Adams' work until someone pointed me to his earlier work, which is much more subtle and natural than the later high-contrast poster stuff.)

  10. #20

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    Quote Originally Posted by Katharine Thayer View Post

    ...

    (I also hated Ansel Adams' work until someone pointed me to his earlier work, which is much more subtle and natural than the later high-contrast poster stuff.)
    It's the advance in technology & technique that ruins Adams' work for you then; the lenses got sharper and more contrasty (better production lines, multi-layer coatings etc.), films got better, also Adams' technique got sharper and stronger... It's not coincidence that people are looking for single coated lenses and/or manufacturers produce "special" single coated optics for B&W photogs. See Cosina's 40/1.4 Nokton SC for instance; you'll definitely get more shadow detail with such a lens...

    Anyway, what distinguish a master from an apprentice is to force the limits with subtlety, I mean w/o the "in your face" attitude... If someone is more attracted to technique (instead of unknowingly appreciate it as a means to transfer the message/emotion) when looking to a photograph then it's probably so a) because of the viewer is a nerd b) because that's an apprentice's work or c) both... Photography (especially B&W photography) is like make-up to me; the best make-up is the one you don't notice its presence, whereas the best photographs are the one you're not attracted to the technique "in the first place". Whether too subtle or overworked...

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