From: Christina Z. Anderson (zphoto@montana.net)
Date: 08/02/03-10:31:40 AM Z
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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