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

Re: Dichromate concentration question

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?