Re: Dichromate concentration question
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 >> 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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