From: Philippe Monnoyer (philippe.monnoyer@skynet.be)
Date: 07/24/02-04:03:27 PM Z
Sandy,
At this point you have a mix of
-sodium ferric citrate
-sodium ferric acetate
-acetic acid
-citric acid (reaction of acetic acid + citrate)
but all these species are separated in ions in the solution. They are Na(+),
Fe(3+), citrate(3-), acetate(-), H(+)
The color of a salt solution depends on the presence of other species in the
same solution. It make complexes that absord the light differently. For
example, a solution of iodine crystals in water or in acetone won't give the
same color. But it's still iodine.
For your process here, what matters is that you have both citrate(-) and
iron(3+) present. The citrate (or oxalate) ions are the ligth sensitive
part. Iron is the species that will take electrons from the citrate and give
it back to the nobel metal, until it is a "black" metal. The smaller the
metal particles, the warmer the tone. In chrysotype, it is even red and
blue. RH% during exposure determines the size of the particles, and the
tone. More RH% gives a faster reaction and bigger particles, and finally a
more neutral tone.
So you used this trick to have your ferric citrate in solution. It seems to
work. Good. It was only a theoretical expectation (or chemical intuition)
from me. The next issues will be:
- is it still sensitive enough ?
- is the contrast improved ?
Maybe the quantity of acetic acid added would play on both ...
Wait and see ... I'm curious
Cheers,
Philippe
----- Original Message -----
From: Sandy King <sanking@clemson.edu>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Wednesday, July 24, 2002 11:21 PM
Subject: RE: Ferric citrate in VDB formulas
> Philippe wrote:
> >
> >To answer your question, a priori, a way to dissolve ferric citrate
> >could be to add citric acid, or maybe acetic acid..., but I am not
> >sure. Or better, add sodium citrate or potassium citrate or lithium
> >citrate. This will make the coreponding salts sodium ferric citrate
> >or potassium ferric citrate or lithium ferric citrate. If one of
> >these salts is highly soluble you solve your solubility problem.
> >
> >
>
>
> I did as you suggested. To 35ml of water I added 10g of ferric
> citrate and 8g of sodium citrate, and about 2ml of acetic acid. It is
> now 24 hours later and most of the ferric citrate has in fact gone
> into solution. The color of the solution is dark green, in contrast
> to the color of ferric citrate solution by itself, which is
> brownish/red. I suspect that by tomorrow the rest of the ferric
> citrate will have gone into solution and then I will be able to test
> the speed and contrast of the solution.
>
>
> My question at this point is, how do I know if the solution is now
> ferric citrate or sodium ferric citrate? Is the green color the key?
>
> Sandy King
>
>
>
> --
>
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