Re: Tartaric Acid as contrast agent in VDB?

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 11:05:10 2004