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What might be a pure acid? Glacial? Or
sulfuric or phosphoric? Or hydrochloric? I have all four
here...
So you are saying that sodium ascorbate (isn't that what
Vit C is) is present to a significant amount in lemons to make more of a
difference than the actual acid in lemon juice?
So the test would be lemon juice against other
acids?
Interesting...
This is what is so useful about this list...
Chris
__________________
----- Original Message -----
Sent: Saturday, September 06, 2008 7:05
PM
Subject: RE: gum preservatves
Chris,
Very informative experiment. I do not think that
effect is due to acidity. I would rather put out a hypothesis that the effect
is due to the vitamin C (ascorbic acid) present in lemon juice. Vitamin C
is a strong reducing agent that would react quickly with dichromate reducing
it to Cr (III) and making gum insoluble. Kind of like a dark reaction in
gum, no light needed. It appears as a stain, but it really is not. It is
really a chemical fog.
ANyways to test acidity one would use
solutions of pure acids.
Marek
> Date: Sat, 6 Sep 2008 15:49:18
-0600
> From: zphoto@montana.net
> Subject: Re: gum
preservatves
> To: alt-photo-process-l@usask.ca
>
> Here it
is:
>
>
http://christinazanderson.com/Text_page.cfm?pID=2076
>
> Scroll
down to the very bottom past the color charts.
>
> I'm not saying
it proves anything, but acidity may account for some problems
> that
people say are issues with gum, and it is only really meaningful in
>
relation to the water control strips done at the same time with the same
> amounts of dilution. Otherwise a lot more tests would have to be done
to be
> conclusive. If, as Ryuji and Demachy said, there is a reduction
to chromic
> acid with the addition of lemon juice, which I don't know
because I am not a
> chemist, I don't know if that is speedier or less
speedy than dichromate.
> Chris
> __________________
>
> Christin a Z. Anderson
> http://christinaZanderson.com/
>
__________________
> ----- Original Message -----
> From: "Loris
Medici" <mail@loris.medici.name>
> To:
<alt-photo-process-l@usask.ca>
> Sent: Saturday, September 06,
2008 3:13 PM
> Subject: Re: gum preservatves
>
>
>
Thank you!
>
> Now that you say that, I remember the section
about it in the "Learn" part
> of your former website. (Adding lemon
juice and staining... I'm not making
> it up right?)
>
>
Judy's note on sizes was interesting and real food for thought, BTW.
>
> Ryuji's notes also were interesting -> I mean the probability of
citric
> acid (or any other organic acids) interacting with dichromate
in an
> unwanted manner. That powered my original position which was
increasing
> the acidity by not adding alien compounds... (Still don't
know if that can
> work or not -& gt; I may do some tests in the
future if the exposure times
> become unbearable to me and/or I can't do
nice casein prints...)
>
> Regards,
> Loris.
>
>
> 5 Eylül 2008, Cuma, 1:12 am tarihinde, zphoto@montana.net
yazmış:
> >
> > ...
> >
> > Have at it,
Loris. I found that the more lemon juice drops
> > I added to the mix
(with drops of water added to the control
> > group in the same
proportion) that I got lots of staining of
> > the highlights and
lower contrast, but with paper negs this
> > might be helpful to
you--I mean, the lower contrast part.
> > Step wedge steps were not
too differentiated.
> > Chris
> >
> > -----
Original Message Follows -----
> > From: Loris Medici
<mail@loris.medici.name>
> > To:
alt-photo-process-l@usask.ca
> > Subject: Re: gum
preservatves
> > Date: Thu, 04 Sep 2008 21:37:54 +0300 (EEST)
>
>
> >>David & Chris, that also arrived to my mind just
after had
> >>sent my last message... Even if I refrain to
introduce
> >>another alien compound into consideration - as a
first
> >>impression -, it sounds interesting / promising. You
can
> >>bet I will try this (with citric acid)as soon as
possible!
> >>Of course there's also the staining issue... I'll
see.
> >>Thanks!
> >>
> >>Chris, do you
know how much lemon juice was Demachy adding
> >>to his
gum?
> >>
> >>Regards,
> >>Loris.
>
>
>
>
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