RE: Ferric citrate in VDB formulas

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From: Monnoyer Philippe (monnoyer@imec.be)
Date: 07/23/02-09:03:47 AM Z


Sandy,

I had the same problem with cyanotypes. I just changed the iron salt from ammonium ferric citrate to ammonium ferric oxalate. This gave me a clearly higher contrast. I wouldn't be surprised that this would behave the same way for VDB.
The keyword here is the iron salt. Liam shortened the scale by using ferric citrate instead of amm. ferric citrate.
Other salts will also work and give different results, like ferric tartrate, oxalate, ... carboxylates in general. You can change the cation too and take sodium ferric citrate, potassium ferric citrate, lithium ferric citrate.
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.
Analogy: Palladium Chloride is not soluble. To dissolve it you add Lithium Chloride and warm gently ... I should dive back in my literature. If it works, let me know. It's easy to test it (sodium citrate is very commonly found). And if you're lucky, this new salt will boost the contrast.

Philippe
Belgium

|-----Original Message-----
|From: Sandy King [mailto:sanking@clemson.edu]
|Sent: Tuesday, July 23, 2002 16:15
|To: alt-photo-process-l@skyway.usask.ca
|Subject: Ferric citrate in VDB formulas
|
|
|I hope that some of the chemists on the list can offer some
|suggestions on a problem.
|
|Background. Sometime in January or February of this year I asked for
|suggestions on getting more contrast with VDB. The classic VDB
|formula as I mix it has a very long ES of about 2.45, with the result
|that most of my negatives print fairly flat. As noted earlier, adding
|dichromate to the sensitizer or to the water during development, does
|not really increase contrast.
|
|In response to my question Liam Lawless sent me the folling note.
|
|
|
|
|
|
|>Sandy,
|>
|>I've done a quick experiment and think the VDB scale can be
|shortened by 3
|>or 4 steps, without increasing printing times or diminishing
|D-max (though
|>results appear to be somewhat variable on different papers).
|To compare the
|>result with straight VDB, have a look at
|>http://www.artphoto.pwp.blueyonder.co.uk/vdb.htm/
|>
|>Instead of 9 g of f.a. citrate in the "A" solution, I used 3
|g f.a. citrate
|>plus 6 g ferric citrate. This is a very fine brown powder
|that looks like
|>powdered rust, and is not very soluble; a sludge forms at the
|bottom of the
|>mixing vessel. Increasing the tartaric acid to about 4 g in
|"B" seems to
|>help dissolve it, but some still remains. It can be filtered
|out, or just
|>take care not to shake it up before using the sensitiser.
|The "C" solution
|>still uses 3.8 g silver nitrate; the modified sensitiser has
|a paler colour
|>but coating and processing are as normal.
|
|
|
|I have found that the mixture of ferric citrate would ammonium ferric
|citrate at the ratio suggested by Liam does indeed result in a
|shortening of the VDB scale by about 3-4 steps as Liam suggested.
|However, it is *very* difficult to get the ferric citrate to go into
|solution. Liam initially mailed me a few grams of ferric citrate in a
|fine powder form which took a couple of weeks to go into solution.
|However, I later purchased some Ferric Citrate in granular form that
|has so far resisted all of my efforts to go completely into solution.
|I have heated the solution and left it standing for days on end but
|there is still a significant part of the ferric citrate that settles
|to the bottom of the bottle. Does anyone have a suggestion as to how
|to make ferric citrate go into solution at the ratio of about 6-7g of
|ferric citrate per 35ml of water?
|
|Sandy King
|
|
|--
|


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