U of S | Mailing List Archive | alt-photo-process-l | Re: Gum Humidity Question

Re: Gum Humidity Question

OK, yesterday I posted the results of printing at 80% or higher in my workroom (cleared easily, half an hour development); this morning the RH in my workroom registers 92% and again, the printing goes as usual.

So the answer to your comment is yes, I can and do print at over 90% IN my work area.

But it looks like I won't be able to get readings over 92%, even if the area is more humid than that, because just out of curiosity I tried putting the thing in an enclosed space and filling the space with steam, and it still read only 92%. So even though I bought it because it claimed to be able to register humidity up to 99%, its actual maximum reading seems to be 92%. And the other one, the cheap one, reads 80%, which seems to be *its* maximum reading.

Besides, if you need more proof that I print without a problem in conditions of high humidity, I can tell you that for a year or so I was printing in a dank cellar that had a stream running through it. I'm not kidding; I had to wear boots to work. It was a spring coming from farther up the hill somewhere; it ran right through the basement, and it ran strong enough that it left a delta of mud around its edges. I didn't have any kind of meter to measure humidity at the time, and didn't care, but I can tell you it was DAMP in that cellar; I wouldn't be surprised if the humidity was close to 100% most of the time. I did some very good work there, even if it wasn't a very pleasant place to work.

Hence my smile when someone opined that the process "doesn't work" over 50% RH. Like I keep saying, it ain't humidity that's the problem.

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.


-----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