RE: Gum Humidity Question
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
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:firstname.lastname@example.org]
> Sent: Tuesday, September 26, 2006 7:51 PM
> To: email@example.com
> 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