Re: old cyanotype formulae

["alnovo@inwind.it" <alnovo@inwind.it>]

On Mon, 20 May 2002 Judy Seigel wrote:

> On Mon, 20 May 2002 CCBaggett@aol.com wrote:
>
> > Photographic Facts and Formulas  E.J. Wall dated 1924
>
> CUT
>
>  "Brighter prints are obtained by the addition of 0.5% of
> > Oxalic Acid to the above; the paper keeps better if 0.05%  of Potassium
> > Bichromate is added."
>
> Potassium bichromate as preservative for cyanotype emulsion may be true on
> the planet Mars... but my finding was that it actually made a terrible
> print under most circumstances... The variables included size added to the
> paper, and which size (gelatin or starch), also how long the emulsion was
> on the paper, and how long the size had been on the paper, among others..
> (I showed some of them in the "cyanotype issue" of P-F, #5, page
> 31).
>
> In fact I found cyanotype poster child for old formulas not printing as
> stated.... My guess is that none of the workers then had the Internet and
> didn't realize how many variables there really were. If something "came
> out" for them in one set of conditions, they assumed it was a universal.
>
> The old books are riddled with stuff like that.
>
> Judy
>

It is higly probable that the purity of the Fe. am. citr. used by Walls in 1924 were not so high, and a very small amount of dichromate (it is 0.05%) would have oxidised the traces of divalent iron, thus giving better whites in the print.

I think that the more-or-less old recipes need to be viewed in their historical context (reagents, papers, ... and tastes), and in many times we are not so able to match all these "historical" variables.

Alberto

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