RE: Shelf Life of Van Dyke Sensitizer

[Judy Seigel <jseigel@panix.com>]

On Sat, 18 Aug 2001, Keith Gerling wrote:
> ... this time I was following the
> directions as outlined in Richard Farber's "Historic Photographic
> Processes", which cautions one to combine the chemicals in an exact order,
> which I did.  Upon adding the Silver Nitrate solution, however, a greenish
> cloudiness formed, and it appeared that the silver did not want to go into
CUT.....
> I can't answer your question regarding shelf life, but it appears that under
> some circumstances the plating can occur within a very short timespan.
> While doing test strips with this new batch of sensitizer, I compared it to
> some pre-mixed sensitizer that I purchased from Bostick and Sullivan over
> two years ago.  The test strips looked very similar, although there was a
> tad less contrast in the older mix.
>
> The Farber instructions are as follows:
>
> 1) add 10 grams Ferric Ammonium Citrate to 10 ml distilled water
> 2) to that, add a solution of 1.5 grams Tartaric Acid and 35 ml distilled
> water
> 3) to that, add a solution of 4 grams Silver Nitrate and 35 ml distilled
> water

In the first place, those amounts are not the classic VDB formula, but
somewhat stronger, which could be part of the problem, but I suspect only
part.

In any place, that's NOT a good way to mix VDB... Each chemical should be
mixed separately in its own water, then A & B combined, and C (the silver
nitrate) added -- for a number of reasons including that if there's
something wrong with your silver (I had a contaminated batch once, a
student also had mixed with tap water, etc.) or for that matter any one of
them, you see that as you don't when you mix all together right off.

Re adding the silver so very very very slowly, that's also (I find)  one
of those superstitions. If you add a bit too fast, you'll see a white
precipitate form at the point of contact, but keep stirring & it
redissolves as rapidly as it forms.

The classic formula (as given in Post-Factory #1, which is if I may be
forgiven for saying so, generally safer than some book I haven't tested,
ESPECIALLY one with naked lady on the cover):

Sol A - 9 g fe am cit in 33 ml water
Sol B - 1.5 g tartaric in 33 ml water
Sol C - 3.8 g silver nitrate in 33 ml water.

This makes 100 ml VDB. I usually mixed 200 to 300 ml at a time, as did Bob
Schramm, who tested several formulas (among other tests) for his P-F #1
article. Of these, the "classic" (also in KOL & Nettles, among others) was
clearly the best.

It keeps indefinitely (or anyway up to 4 years) in brown glass bottle. As
it ages, you'll often see black precipitate in the solution but that
redissolves on coating. If you're not getting good D-max, you may be...

heat drying (lowers D-max, on some papers blows it right out)

not coating properly (ie, not wetting paper enough)

using stupid paper

adding gelatin size to paper

adding some cockamamie ingredient, like gum arabic, to emulsion

having bad chemicals

not using distilled for emulsion

fixing too long (2 minutes absolute MAXIMUM, after which fixer bleaches)

or fixer too strong, try 26 g am thio to (is it a litre? this from memory)
water

or possibly not washing ENOUGH in the water before putting in fixer. Do a
time test... Sometimes with thicker paper this first wash has to be longer
than 5 minutes...

etc. etc. etc. etc.

As for silver coating on inside of bottle, I too have found that happens
quite promptly sometimes.  Did NOT affect D-max. My guess is all that
silver isn't going into the print anyway (as witness milky runoff during
first wash -- that's silver chloride).

Judy

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| Judy Seigel, Editor                           >
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