RE: Shell Life of Van Dyke Sensitizer

[Keith Gerling <kgerling@ameritech.net>]

Sandy,

Recently I had an experience which I thought was odd.  I was mixing up a
batch of Van Dyke sensitizer for the first time in a couple of years.  I do
not recall how I mixed it before, but 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
the solution.  After stirring for several minutes, I gave up and warmed the
solution in a microwave.  Within a minute, the solution looked fine: the
dark greenish solution appeared as I had originally expected it to look.  I
made a couple of prints, and they looked OK.  The next day, however, I had
the same situation on my hands that you report: a nice silver plating on the
inside of my bottle.  I still get the same kind of results I had before the
plating.  (I won't say that I still get good results, because I have always
got a weak DMAX with Van Dyke, but that's another story....)

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

Keith

-----Original Message-----
From: Sandy King [mailto:sanking@clemson.edu]
Sent: Saturday, August 18, 2001 12:46 PM
To: alt-photo-process-l@sask.usask.ca
Subject: Shell Life of Van Dyke Sensitizer


Hi folks,

This morning I pulled out an old bottle of Brown Dyke Sensitizer,
mixed about a year ago, that had been left for many months with a
small quantity of sensitizer in the bottom, to a depth of about 3/4".
What I found was a perfectly beautufly coating of silver plating on
the inside of the bottle (but very shiny when views from the outside
through the amber colored plastic). Given the fact that the silver
has left the solution and formed a nice plating on the side of the
bottle makes it pretty obvious that the shelf life of this particular
bottle was quite a bit less than a year.

Which brings me to this question. What is the effective shell life of
Van Dyke sensitizer, assuming that it is kept in a brown, tightly
capped bottle, and stored at room temperature in the dark, or in very
subdued light?

Any comments about this, or other specific information about storing
this sensitizer, appreciated.

Sandy King