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

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
>> 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?
>>>>>
>>>>>
>>>>
>>>>
>>>>
>>>
>>>
>>>
>>
>>
>
>