Re: humidity and gum coating
On Sep 2, 2006, at 4:48 PM, Tom Sobota wrote: The RH here stays more or less put at 20% during the summer months, but I see that you have rather fast daily changes.Well, what happens here is that the humidity is over 90% most of the time, except in the late summer and fall, when it's more like 75-80%. But maybe two or three times a year there's this thing where the wind swings around and comes down the Columbia Gorge from the desert all the way to the coast. When that happens, the humidity plummets, as it did the other day down to 17%. If it happens in summer it's suddenly hot and dry, and if it happens in winter it's suddenly cold and dry; otherwise the climate is pretty much 50s and 60s (F) and damp the year around. You can see how it would wreck havoc with my gum practice when this happens, since it's such a dramatic change from the usual conditions. But this is also why I'm so aware of the effect of humidity on gum, not just on coating but on printing, since when this happens I'm suddenly having to double and triple my printing times and still finding that the film isn't exposed enough, and then when the wind switches back around to the west, everything goes back to normal again. People are always asking me about the "troubleshooting" section on my website, which so far is nonexistent; the label is there to remind me I was going to have a troubleshooting section on there someday. I've been revising the site, and part of the revision will be to finally add this troubleshooting section. So last night I had fun making a page about this problem, just in case it might be useful to someone. It looks like most people who are faced with this problem more often than I am have already come up with ways to deal with it, but perhaps it might be helpful to someone out in the desert somewhere who is taking up gum printing in isolation. http://www.pacifier.com/~kthayer/html/unevencoating.html I added the print I made on wet-coated Arches bright white yesterday to the one I re-posted yesterday; they are linked to the page with a link to "results" of printing on wet-coated paper, toward the bottom of the page, if you're interested. Katharine
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