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 20°C. 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 -30°C (-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 -22°F > 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, 5-14°F). 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? >>> >> >> > >
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