Re: Tartaric Acid as contrast agent in VDB?

Loris,

I have seen many claims about being able to alter contrast in VDB
(adding potassium dichromate to the sensitizer or to the water bath,
adding tartaric acid, adding other acids, etc.) but they never worked
in my tests and my belief is that these methods don't work at all,
even though some of them have been recommended in the most recent
books on alternative printing. The only thing that worked for me in
increasing contrast in VDB was to mix some ferric citrate with the
ferric ammonium citrate. This method was described by me a couple of
years back on the list and you could find it in the archives, and it
was also published by Judy Seigel in a recent number of Post-Factory
Photography.

As for your second question, I don't really know the answer. However,
VDB is a POP process so that there is some self-masking going on
during printing, which could explain in part your phenomenon.

Sandy

>I see,
>
>I thought adding some "organic" stuff (tartaric acid is organic isn't it?)
>would increase sensivity of silver-nitrate (or silver-whatever that forms
>when you mix A and B and C solutions)... Can't recall where but I remember
>reading this somewhere - considering your and Sam's test results I guess I
>misinterpreted what I read. What about my 2nd question?
>
>"One more interesting fact is that if I vary the exposure considerably
>results don't change by the same proportions. For instance once I tried 8, 2
>and 16 min. exposure with the same lith negative and only midtones and
>highlights were affected - highlights more, deep shadows almost none... As
>if the emulsion was self masking!? What can be your comments for this
>phenomenon?"
>
>Thanks,
>Loris.
>
>----- Original Message -----
>From: "Sandy King" <sanking@clemson.edu>
>To: <alt-photo-process-l@sask.usask.ca>
>Sent: Saturday, January 03, 2004 6:31 PM
>Subject: Tartaric Acid as contrast agent in VDB?
>
>
>> It has been some time since I did any VDB printing but tests I did a
>> couple of years ago in increasing the amount of tartaric acid in the
>> sensitizer in an attempt to increase contrast indicate that it did
>> not work. As best I recall sensitivity was decreased but actual
>> contrast (as evaluated by the actual exposure scale of the print as
>> judged by the results of printing a 21 step tablet) did not change at
>> all. So, the practical consequence of adding the tartaric acid may be
>> just an increase in printing times, which could explain, at least in
>> part, why your exposures appear to be so long.
Received on Sat Jan 3 12:17:36 2004