U of S | Mailing List Archive | alt-photo-process-l | Re: Dichromate concentration question

Re: Dichromate concentration question



I will not say a thing about cold out here for we are having an
unseasonable heat spell and fear
drought. I will say it was 30 below once in NV when there and I found
it surprisingly not that cold.
Oh . . . . welllll, certainly it was cold, in fact extremely, but, in
that odd way of living, it was just fine to
walk around in, etc.

On Jan 15, 2009, at 5:02 PM, Katharine Thayer wrote:

Oh, hmm, so it's actually warmer in your studio than it was in mine
last winter. But I'm glad you've got Toastie Toes, whatever they
are; it sounds like something meant to keep your feet warm. My main
problem working in cold weather, other than the gum congealing, was
putting my hands in the cold water; gosh that water was cold, just a
few degrees above freezing. Thanks for easing my curiousity, and
happy printing....
Katharine



On Jan 15, 2009, at 4:12 PM, Keith Gerling wrote:

Katherine,

I'm sorry that I said it was only a tad warmer in the studio than the
23 below outside. It was 6:00 AM and I hadn't had my coffee. It
FELT
like it was freezing, but it was probably 45 degrees. ( so actually,
it was a huge difference)

Yes, the dichromate did settle out of the saturated solution. And
no,
I don't have any problems coating the gum. With the very low
humidity
I don't even have to use a hair dryer. And I received a box of these
Toastie Toes as a Christmas gift. so I'm fairly comfortable

http://www.amazon.com/s/qid=1232064603/ref=sr_kk_1?ie=UTF8&search-alias=aps&field-keywords=toastie%20toes


On Thu, Jan 15, 2009 at 3:06 PM, Katharine Thayer <kthayer@pacifier.com
> wrote:

Keith, I'm glad someone knew where a chart was (glad to know about
that
myself) but I'm curious about something. You didn't mention
having a lot of
the dichromate settle out of solution, which would be what would
happen as
the solubility decreased with the temperature. Did you start out
with a
saturated solution?

Also, I'm curious about your experience printing at such low
temperatures,
because I found last winter that I simply couldn't work in the
cold; the gum
simply wouldn't coat the way it should and prints were ruined
because of the
streaking and weirdness of the gum. And this was at much warmer
temperatures than you're talking about (above freezing). It
sounds like
you've had no trouble with the gum itself, only with the
exposures. I don't
think I had to adjust temperatures for the cold, but then it was
only 30
degrees below normal room temperature.
Katharine



On Jan 15, 2009, at 12:46 PM, Keith Gerling wrote:


OK, so I was exaggerating. A tad. Now that the sun is warming the
studio, it is 10 C and according to the chart, I'm getting a
little
more that half the amount of dichromate that I would at a more
typical
20C. That is significant.

Thanks for the link. That chart is fascinating and I'm doing
really
well on the test.

On Thu, Jan 15, 2009 at 11:55 AM, Dirk-Jan Treffers
<dirkjan.treffers@gmail.com> wrote:


Hi Keith,

just for fun, check
http://www.sciencegeek.net/Chemistry/taters/solubility.htm
The line for K2Cr2O7 (pot dichrom) drops dramatically when
reaching 0 C
(32 F).... Although it looks like the lower the temp gets, the
more
asymptotic the line becomes....
Try printing the graph on a bigger piece of paper, and draw the
x-axis
further to the left, and see where the graph would more or less be
(concentration-wise) at -30C (-22 F)....

My guess would be 3-4%. That seems not nearly enough to really
become
light-sensitive.... Try Chris's suggestion to use Am-dichrom.
Maybe at
-22F
that would result in a higher concentration of dichromates....


Good luck with the icy temperatures.... Here in Holland we just
experienced
-10 to -15 (night time, 5-14F). At those temperatures,
everybody is
hoping
for an 'elfstedentocht' (eleven-city tour, a 200 km ice-skating
tour
trough
eleven cities, something 90% of the Dutch wants from time to
time. See
http://en.wikipedia.org/wiki/Elfstedentocht )... Ok, enough off-
topic
nonsense.....


deejay




2009/1/15 Christina Z. Anderson <zphoto@montana.net>



LOL poor you, Keith--apparently this cold snap missed Montana,
but is in
MN big time. It is in the 30's and 40's outside so it feels
like spring
to
me here, but my son is experiencing -38.

You're not SERIOUS when you say your studio is only a "tad"
warmer than
-23, are you????? Is your dichromate solution an ice cube???

As far as pot di, this is, again, a reason I prefer am di
because down
to
32 degrees am di is still 15% soluble, and that is what I use
it at
anyway.
But if pot di starts at 10% solubility max, I've read it goes
down to
about
5% at colder temps (not -23 though!!). BUT I have no idea how
this
correlates to exposure so am not answering your question, only
guessing
that
a stop more exposure might be it.
Chris
__________________

Christina Z. Anderson
http://christinaZanderson.com/
__________________
----- Original Message ----- From: "Keith Gerling"
<keith.gerling@gmail.com>
To: <alt-photo-process-l@usask.ca>
Sent: Thursday, January 15, 2009 5:53 AM
Subject: Dichromate concentration question




As I sit typing the temperature outside is -23F. My studio is
a tad
warmer, but I have noticed a dramatic change in what I need for
printing times for gum. We all know that "saturated"
solutions change
with temperature, and the cautious printer will weigh out the
chemicals. But is there a multiplier I can apply to my printing
speeds that will take into account the actual amount of
ingredients
contained in my "saturated" solution of Potassium Dichromate at
different temperatures?