From: Sandy King (sanking@clemson.edu)
Date: 07/25/02-08:26:14 AM Z
Philippe wrote:
>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
Philippe:
OK, today the solution with sodium ferric citrate had cleared
completely and I mixed up a VDB solution with ferric citrate and ran
a comparison test of this solution with a classic VDB solution
containing ammonium ferric citrate. Exposure of a Stouffer TP 45 step
wedge was with BLB tubes for 10 minutes.
Results:
Classic VDB solution with AFC: First maximum black at Step 4, last
visible step at Step 20, or a total scale of 18 steps.
VDB with ferric citrate: First maximum black at Step 4, last visible
step; at Step 17, or a total of 14 steps.
Comments: The VDB with ferric citrate prints with the same speed but
with much more contrast, about four steps or two full stops. The
color is about the same, dark brown in both cases, but the maximum
density of the classic formula appears to be just a bit higher. On
the densitometer the maximum black of the classic formula with AFC
reads 1.40 while the maximum black with the FC reads 1.34.
I have just mixed a solution of 10g of ferric citrate and 10g of
sodium citrate in 35ml of water, but without the acetic acid. It
appears to be going into solution rather well so I hope to be able to
avoid the acetic acid, which may have bleached the silver in the
previous tests and caused the slightly lower maximum density reported
above.
Sandy King
>
>----- 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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