Re: Gum Humidity Question
On Sep 26, 2006, at 8:32 PM, Kerik wrote:
OK, you live on the coast and it's foggy outside so the humidity is
near
100%. When you get a hygrometer ($30 from radio shack - been using
them for
years), it would be interesting to know what the conditions are in
your
darkroom/work area.
The humidity in the workroom should be pretty close to the humidity
outside, shouldn't it, as long as the windows are always wide open?
I's not fog, BTW, it's just a constant dampness in the air, and
believe me, when it's damp outside, it's damp inside, if the windows
are open. (I just happen to like feeling like I'm living outside,
even though I don't actually want to LIVE outside). But it sounds
like you're saying that even with the house open to the outdoors, the
humidity should be considerably less inside. If that's true, maybe my
cheap hygrometer does work after all.
I've been trying to get one of those Radio Shack hygrometers, but
the Radio Shacks here keep telling me they have them on order, but
they never seem to come in.
Katharine
On Sep 26, 2006, at 8:32 PM, Kerik wrote:
OK, you live on the coast and it's foggy outside so the humidity is
near
100%. When you get a hygrometer ($30 from radio shack - been using
them for
years), it would be interesting to know what the conditions are in
your
darkroom/work area.
We get several 100% humidity days where I live, but the humidity in
my work
area is more like 50 to 60% in those conditions. The 80% and 80
degrees we
had on Sunday were measured IN the work area. I've read that these
inexpensive hydrometers read a bit on the low side, so it may have
been a
little higher than that.
This is all good information, though. Weather it's speed or an
effect on the
sizing or something else, something is definitely going on here.
Kerik
-----Original Message-----
From: Katharine Thayer [mailto:kthayer@pacifier.com]
Sent: Tuesday, September 26, 2006 7:51 PM
To: alt-photo-process-l@usask.ca
Subject: Re: Gum Humidity Question
On Sep 26, 2006, at 4:32 PM, ericawd wrote:
I can tell you that much above 55% RH, the process does not work.
This made me smile, not at you, but at the futility of
making categorical statements about gum, since most of my
work is printed at between 90 and 100% RH, and the process
works just fine. Obviously there's something else going on,
some other variable, that must account for the difference
between our observations about humidity.
Curious whether I could see any difference in contrast, I
looked at the data I'd gathered so far on my little
experiment. I've used the
same pigment mix throughout (Prussian blue), mixed 1:1 with
saturated ammonium dichromate. For the humidity readings for
these test strips, I used the current reading from the noaa
statiion at the local airport. My exact readings here will
vary somewhat from the airport, which is why I decided I
should get a hygrometer to get accurate readings in my
workroom, but the airport readings shouldn't be more than a
few percentages different from mine, as I'm near a large body
of water and so is the airport, and it's just on the other
side of the hill from me.
I had the test strips sorted into envelopes by humidity
range, so it was easy to line up the test strips from the
different envelopes and see if there's any difference in
contrast between the test strips from the different envelopes.
At each of the humidity ranges (60-70%; 70-80%; 80-90%, and 90-100%)
this particular coating mix printed an optimum 7 steps. But for
each humidity range, the exposure needed to print those 7
steps was different.
There is possibly a slight difference in the separation
between the steps at the different humidity ranges; the test
strips at over 90% seem to have slightly more apparent tonal
separation between the steps than those printed at lower
humidity, but not enough to make
the darkest and lightest tones seem noticeably different. So I
guess at this point I would have to say tentatively, no, I
don't see a difference in contrast at different humidity
levels, at least within this range of humidity (60-100%).
Thank you for your input. Good luck finding a decent hygrometer.
Thanks too. What I'm finding is that hygrometers tend to
measure less and less reliably the farther they get from
50-60%, so it's going to be difficult to find one that will
give me accurate readings in my normal humidity range. Thanks
for posing an interesting question, Katharine
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