Re: Measuring humidity
I was reading what you quoted and decided to see if there was more info, so I dug out my old Kosarnart manual and couldn't find anything but how to do julienne style french fries.....sigh.
Precision Digital Negatives - The System
PDNPrint Forum at Yahoo Groups
In a message dated 9/29/06 9:41:54 AM, firstname.lastname@example.org writes:
Returning to part of my Kosar post of now years ago (point 5-9 of Kosar's
Top 10--it's interesting that we are now using Kosar as an authority because
when I quoted him years ago I got all sorts of flak about his information!
My how times change...speaking of never being heard, HA! Mark I have you
beat on that in spades):
5. PH, temperature, and moisture all affect printing speed.
6. Adding an alkali to the gum/dichromate mix: if so much is added it is
converted into a monochromate, and the light sensitivity drops to 25%. The
higher the pH of the layer, the> longer the required exposure. Chromates,
thus, are slower than dichromates.> With ammonia, you may start out with a
high pH in solution, but due to> the volatility of ammonia, it evaporates
during drying and the pH of the coated layer returns to a lower pH. If a
solid alkali is used (sodium hydroxide or carbonate) the alkalinity of the
dried layer remains the same.> The useful life of a sensitizing *solution*
is greatly increased with addition of ammonia. If pH is 8 or higher,
deterioration of solutions is practically nonexistent (note: not coated
7. Humidity: The presence of a certain amount of moisture in a coated and
dried layer is necessary for the hardening reaction. When dry, the moisture>
remaining varies with relative humidity. Completely dehydrated or fully
swollen coatings do not show any light sensitivity at all, but in between
the sensitivity is high when the humidity is high. Sensitivity doubles with>
increase of 30% humidity.
8. Paper will keep, coated, for even 70 days in the ice box, or 3 days at
room temp. If paper is dried at room temp high enough to dehydrate coating,>
dark reaction does not occur and consequently shelf life is very good.
9. Raise in temp increases rate of chemical reactions, and for each 10
degree centigrade raise there is a 3x dark reaction rate, if rH is
Since none of us, I presume, are going to run hundreds of tests to prove
which has a greater effect on dark reaction (what a waste of time) maybe we
can be assured of saying that pH, temp, and humidity both in the air and
within the coated paper has an effect on dark reaction. In my book, Kosar
comes closest to scientifically testing this all, but true, he was NOT a gum
Mark Nelson aside, we are talking here not of spontaneous hardening (which I
take, in the old lit, to mean "instant" hardening that was said to occur
with some pigments, or instant untimely hardening as in Mark's case) but a
hardening that occurs over time to a speedier or slower degree. And yes,
Mark, it seems to me when you brought up the humidity issue a number of
months back, you were dissed, and now you aren't. Hmmm, your lucky
underwear must be working......
My temps were consistent in SC but the humidity was consistently greater
down there than even the most humid day in MT will be. When I did a series
of gums--9 was the most I could seem to do successfully at one time--the
7-9th ones were recalcitrant in development. Here I don't see a problem
with 13. For me, humidity messes with development a bit, but not enough to
make printing impossible, just less predictable. I just have to work harder
and say more swear words.
I can't necessarily apply my experience straight across the board to another
gum printer because one would have to take into account exposure time,
source, pigment layer, layer thickness, and all those other things, too. I
can only apply it to my own practice because there I can compare apples to
apples. When someone down South says gum "doesn't work" I can understand
that feeling totally. And I can suggest these three culprits to be at
fault, but certainly can't quantifiably suggest one is more important than
the other unless I am willing to run 100 little tests.
Sandy, when you teach carbon at the Photographer's Formulary do you adjust
your practice to suit the dryness there?