From: Larry Roohr (larry.roohr@comcast.net)
Date: 08/02/03-09:38:41 AM Z
No, I'm serious. If % soluble means %in solution, and it does get to 89%
at 86degF, then one could get the amount of dichromate into the mix
Stuart does with the same amount of water without having to do the dry
measurement thing. If the liquid dichromate is kept as you do, with a
sludge of available dichromate at the bottom to go into and out of
solution as the temp changes, this should be manageable. But, I slept
through my one required chemistry class in college, so this could just
amount to twisted thinking on my part (not that that ever happens 8^).
Larry
Christina Z. Anderson wrote:
>Larry,
> You are toooo funny.
> The only thing I will do with Kosar's info is to assume that if my
>darkroom is really hot, that there will be more dichromate in my sensitizing
>solution than I think. If I encounter this situation I will be sure
>measure out my dichromate solutions with a scale. If you have a 30% di
>solution of am di, it will not become more saturated at higher temps than
>30%, since there is no more di to be had. Back in MT where there is not the
>change in temp or humidity in my basement (to any appreciable extent) I can
>be assured of predictable results with the "dump and pour" method.
> But I think you are making a point in a roundabout way that the dry
>dichromate method may be a superior method of accuracy? :)
>Chris
>----- Original Message -----
>From: "Larry Roohr" <larry.roohr@comcast.net>
>To: <alt-photo-process-l@sask.usask.ca>
>Sent: Saturday, August 02, 2003 9:39 AM
>Subject: Re: Kosar's Top 10 Gum Facts
>
>
>
>
>>Thanks Christina.
>>
>>This seems to mean that Stuarts thick mix of 10ml gum + 2gm AmmDi (dry) +
>>2.5ml water could be gotten pretty close to with liquid dichromate
>>
>>
>solution
>
>
>>by keeping your saturated sludge mix at 86Fdeg for an 89% saturated
>>
>>
>solution
>
>
>>and just using 2.5ml of it, with no nervous-making dry powder mixing, no?
>>
>>Larry
>>
>>----- Original Message -----
>>From: "Christina Z. Anderson" <zphoto@montana.net>
>>To: <alt-photo-process-l@sask.usask.ca>
>>Sent: Thursday, July 31, 2003 9:07 AM
>>Subject: Re: Kosar's Top 10 Gum Facts
>>
>>
>>
>>
>>>Hi Larry!
>>> Yes, that's it. I don't think you need a constant temp water bath
>>>
>>>
>by
>
>
>>>any means--it just means that it may be bests for repeatable results to
>>>
>>>
>>use
>>
>>
>>>a specific concentration measured out by grams instead of the "dump and
>>>pour" method I do. I put the pound of dichromate in a jar and cover it
>>>
>>>
>>with
>>
>>
>>>distilled water, assuming it'll have a saturated solution at the top of
>>>
>>>
>>the
>>
>>
>>>jar and sludge at the bottom, and that the saturated solution at the top
>>>
>>>
>>of
>>
>>
>>>the jar will be (approx) 10% for pot di and 30% for am di. Now I
>>>
>>>
>realize
>
>
>>>that isn't a good method at all unless my temperature of my darkroom is
>>>fairly constant within 5 degrees or so. In MT it is--I am in a basement
>>>where it remains cool and dry. Here I am in a floor level darkroom
>>>
>>>
>which
>
>
>>is
>>
>>
>>>about 80 degrees in the summer and wet.
>>> The only thing I will now change in practice is to measure my
>>>dichromate solutions with a scale before I mix. But that's OK--I was
>>>
>>>
>going
>
>
>>>to do that anyway because I want to figure out the minimal amount I can
>>>
>>>
>>use
>>
>>
>>>and still get acceptable times of exposure.
>>>Chris
>>>
>>>----- Original Message -----
>>>From: "Larry Roohr" <larry.roohr@comcast.net>
>>>To: <alt-photo-process-l@sask.usask.ca>
>>>Sent: Thursday, July 31, 2003 9:28 AM
>>>Subject: Re: Kosar's Top 10 Gum Facts
>>>
>>>
>>>
>>>
>>>>Christina,
>>>>
>>>>Thanks for doing this, lotsa meat there. Am I reading #2 correctly?
>>>>
>>>>
>>Does
>>
>>
>>>>this mean the saturated solution content per volume varies with temp?
>>>>
>>>>
>>>yikes.
>>>
>>>
>>>>Maybe a constant temp water bath is in order.
>>>>
>>>>Larry
>>>>
>>>>----- Original Message -----
>>>>From: "Christina Z. Anderson" <zphoto@montana.net>
>>>>To: <alt-photo-process-l@sask.usask.ca>
>>>>Sent: Thursday, July 31, 2003 7:53 AM
>>>>Subject: Kosar's Top 10 Gum Facts
>>>>
>>>>
>>>>
>>>>
>>>>>Good morning all!
>>>>> I finished taking notes out of Kosar's 60p chapter on
>>>>>
>>>>>
>Dichromated
>
>
>>>>>Colloids (AND a momentous day--finished all my notes from all
>>>>>
>>>>>
>>>>sources--what
>>>>
>>>>
>>>>>a relief-68pp 11pt type is DONE). Since I know not everyone has
>>>>>
>>>>>
>>Kosar
>>
>>
>>>>(out
>>>>
>>>>
>>>>>of print, costs $135 or more to get used) I thought I'd share the
>>>>>
>>>>>
>>items
>>
>>
>>>I
>>>
>>>
>>>>>found of interest in that chapter.
>>>>>
>>>>>MY KOSAR'S TOP 10:
>>>>>
>>>>>1. Certain pigments may be found to react with dichromate causing
>>>>>spontaneous insolubilization without any exposure. (this is probably
>>>>>
>>>>>
>>the
>>
>>
>>>>>source of why some pigments "don't work")
>>>>>
>>>>>2. Ammonium dichromate at 15 degrees Celsius (59 F) is 30.8%
>>>>>
>>>>>
>soluble.
>
>
>>>At
>>>
>>>
>>>>>30 degrees Celsius (86 F) it is 89% soluble! Thus, the method of
>>>>>
>>>>>
>not
>
>
>>>>>measuring out dichromates and always keeping them in saturated
>>>>>
>>>>>
>>solution
>>
>>
>>>is
>>>
>>>
>>>>>probably not a good idea if temp varies greatly in your workplace.
>>>>>
>>>>>3. Two reasons for am di's faster speed is its high solubility
>>>>>
>>>>>
>>without
>>
>>
>>>>>precipitating and its lower pH than either potassium or sodium
>>>>>
>>>>>
>>>>dichromates.
>>>>
>>>>
>>>>>It is pH 4.5. 2.5% ammonium dichromate is the same speed, contrast,
>>>>>
>>>>>
>>and
>>
>>
>>>>>keeping quality as 3.5% potassium dichromate. In a comparison chart
>>>>>
>>>>>
>>>using
>>>
>>>
>>>>>albumin, gum, and process glue, these are the comparative speeds of
>>>>>
>>>>>
>>the
>>
>>
>>>>>three dichromates: ammonium is 100/100/100 potassium is 20/46/65
>>>>>
>>>>>
>and
>
>
>>>>sodium
>>>>
>>>>
>>>>>is 28/100/100. Note the different speeds for the different colloids,
>>>>>
>>>>>
>>>>except
>>>>
>>>>
>>>>>for ammonium dichromate.
>>>>>
>>>>>4. Viscosity varies not only from batch to batch, but with age of
>>>>>
>>>>>
>>gum,
>>
>>
>>>>>which makes the sensitizing properties inconsistent.
>>>>>
>>>>>5. PH, temperature, and moisture all affect printing speed.
>>>>>
>>>>>6. Adding an alkali to the gum/dichromate mix: this changes it
>>>>>
>>>>>
>from
>
>
>>>>orange
>>>>
>>>>
>>>>>to lemon yellow; if so much is added it is converted into a
>>>>>
>>>>>
>>>monochromate,
>>>
>>>
>>>>>and the light sensitivity drops to 25%. The higher the pH of the
>>>>>
>>>>>
>>layer,
>>
>>
>>>>the
>>>>
>>>>
>>>>>longer the required exposure. Chromates, thus, are slower than
>>>>>
>>>>>
>>>>dichromates.
>>>>
>>>>
>>>>> With ammonia, you may start out with a high pH in solution,
>>>>>
>>>>>
>but
>
>
>>>due
>>>
>>>
>>>>to
>>>>
>>>>
>>>>>the volatility of ammonia, it evaporates during drying and the pH of
>>>>>
>>>>>
>>the
>>
>>
>>>>>coated layer returns to a lower pH. If a solid alkali is used
>>>>>
>>>>>
>(sodium
>
>
>>>>>hydroxide or carbonate) the alkalinity of the dried layer remains
>>>>>
>>>>>
>the
>
>
>>>>same.
>>>>
>>>>
>>>>> The useful life of a sensitizing *solution* is greatly
>>>>>
>>>>>
>increased
>
>
>>>with
>>>
>>>
>>>>>addition of ammonia. If pH is 8 or higher, deterioration of
>>>>>
>>>>>
>solutions
>
>
>>is
>>
>>
>>>>>practically nonexistent (note: not coated paper).
>>>>>
>>>>>7. Humidity: The presence of a certain amount of moisture in a
>>>>>
>>>>>
>coated
>
>
>>>and
>>>
>>>
>>>>>dried layer is necessary for the hardening reaction. When dry, the
>>>>>
>>>>>
>>>>moisture
>>>>
>>>>
>>>>>remaining varies with relative humidity. Completely dehydrated or
>>>>>
>>>>>
>>>fully
>>>
>>>
>>>>>swollen coatings do not show any light sensitivity at all, but in
>>>>>
>>>>>
>>>between
>>>
>>>
>>>>>the sensitivity is high when the humidity is high. Sensitivity
>>>>>
>>>>>
>>doubles
>>
>>
>>>>with
>>>>
>>>>
>>>>>increase of 30% humidity.
>>>>>
>>>>>8. Paper will keep, coated, for even 70 days in the ice box, or 3
>>>>>
>>>>>
>>days
>>
>>
>>>at
>>>
>>>
>>>>>room temp. If paper is dried at room temp high enough to dehydrate
>>>>>
>>>>>
>>>>coating,
>>>>
>>>>
>>>>>dark reaction does not occur and consequently shelf life is very
>>>>>
>>>>>
>good.
>
>
>>>>>(Katharine, with the relative humidity in Montana being so low, this
>>>>>
>>>>>
>>is
>>
>>
>>>>why
>>>>
>>>>
>>>>>I could use sensitized paper for so long without dark reaction
>>>>>
>>>>>
>ruining
>
>
>>>it
>>>
>>>
>>>>>there. Here in MN where it is dripping, this is not the case).
>>>>>
>>>>>9. Raise in temp increases rate of chemical reactions, and for each
>>>>>
>>>>>
>>10
>>
>>
>>>>>degree centigrade raise there is a 3x dark reaction rate, if rH is
>>>>>
>>>>>
>>>>constant.
>>>>
>>>>
>>>>>10. In there was the answer to my manganese sulfate question.
>>>>>
>>>>>
>>>Apparently
>>>
>>>
>>>>>"back in the day" they added various things to the sensitizing
>>>>>
>>>>>
>>solution
>>
>>
>>>to
>>>
>>>
>>>>>speed it up, and this was one (that didn't work). Cupric chloride
>>>>>
>>>>>
>>added
>>
>>
>>>>to
>>>>
>>>>
>>>>>dichromated glue increased its sensitivity 2-4x, with just 1/10 of a
>>>>>
>>>>>
>>per
>>
>>
>>>>>cent. The action that happened was to either promote the reduction
>>>>>
>>>>>
>of
>
>
>>>the
>>>
>>>
>>>>>di ion to chromic ion, which then hardens the colloid, or to
>>>>>
>>>>>
>partially
>
>
>>>tan
>>>
>>>
>>>>>the colloids themselves. All these methods have also been found to
>>>>>accelerate the dark reaction. Thus it is not good to store these
>>>>>
>>>>>
>>papers
>>
>>
>>>>at
>>>>
>>>>
>>>>>all. Manganese sulfate was first suggested, but this did not
>>>>>
>>>>>
>improve
>
>
>>>the
>>>
>>>
>>>>>sensitivity, but it was one additive that did not increase the dark
>>>>>reaction. Copper sulfate and cobalt chloride were not as good.
>>>>>
>>>>>
>Other
>
>
>>>>>sensitizer increasers were copper, cobalt, nickel, and rare earth
>>>>>
>>>>>
>>salts.
>>
>>
>>>>> As they used to say on Saturday Night Live Coffee Talk, "Tawk
>>>>>
>>>>>
>>>amungst
>>>
>>>
>>>>>yorselfs..."
>>>>>Chris
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>
>
>
>
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