From: Sil Horwitz (silh@earthlink.net)
Date: 06/22/00-06:36:05 PM Z
At 2000/06/22 06:34 PM -0400, Judywrote:
>OK Sil, now we've got you where we want you --- PLEASE !! Or somebody: I
>understand the great difference in chemistry, that VDB is a silver-iron
>process, action totally different, etc. But in choosing between the two:
>
>There are serious reservations about VDB archivality -- the finely divided
>silver being easily evaporated -- or whatever. Is the salted print more
>archival? If so, that would be reason enough to choose it, unless there's
>a great difference in some other respect...???
>
>VDB is extremely easy, emulsion keeps forever so no need to mix more than
>once a year, and then just coat it on. I've never done salted paper, but I
>know there are at least two baths, possibly 3 at the time of printing.
>I've always figured there had to be a reason for so much trouble, then
>thought oh well, nostalgia is powerful.
>
>Then what about looks -- to a gum printer, needless to say, a brown print
>is a brown print. Gold-toned VDB does darken some, but still doesn't look
>that different. Does a salted paper print look very different from a VDB?
(Normally, I don't copy all of a message, but it seemed necessary here,
because I'd like to dispel some confusion.)
As you know, there are two very closely related processes: Kallitype and
VanDyke. They are similar, but very different. Kallitype uses ferric
oxalate and silver nitrate, which is then developed in various combinations
of buffered organic compounds to provide brown, sepia, blue (!), gray,
maroon, and goodness knows what else. VanDyke is much simpler, using only
ferric ammonium citrate and silver nitrate, and just washed after exposure,
then fixed, giving a pretty horrible color which definitely requires
toning. The process in both is that the ferric ion, upon exposure, becomes
ferrous which then reduces the silver compound (note that silver nitrate is
only slightly light-sensitive and in these processes it is the iron that
does the work) to very finely divided silver which is normally an ugly
yellow-brown. This color is improved by a clumping mechanism (the larger
the silver grains, the blacker the color) during development in Kallitype,
or in VanDyke by toning with gold (unlike salt prints, the toning must be
done after fixing).
OK - permanence. Very finely divided silver is reactive to all kinds of
stuff in the environment, particularly sulfur gases which are omnipresent.
In the large grains (Kallitype) there isn't as much surface to react with,
so it doesn't appear to change (but, if not gold-plated, it will
eventually). VanDyke images consist of these very finely divided silver
particles, and one must be extremely careful of using the absolute minimum
fixer necessary (you can bleach the entire print if placed in standard
fixer) and then toned with gold, which plates the tiny particles. Gold
reacts with iron, which is why the toning must be done after fixing.
Now, this is personal: I like salt prints because they are so easy to make
and if done right give a beautiful brown-black. No iron to worry about, no
concern about residuals, etc, etc. Unfortunately, there isn't much tone
control with salt prints, which is why I imagine the iron processes are
used, though VanDyke isn't as controllable as Kallitype. Probably also,
since when they were created iron salts were cheaper than silver, and these
two processes use less silver nitrate than salt prints, there was the
factor of economy; this no longer applies as in the small quantities we use
the difference in cost is negligible.
Let's face it: there are many processes, each with many variations. You use
what you are comfortable with, and which give you what you want. As I say,
this is personal, but I prefer salt prints over VanDyke because of the
better POP, ease in preparation (OK, you can't keep the sensitized paper,
but you're sure of using fresh materials each time), and greater assurance
of permanence. (To be honest, I worked with Kallitype only once, during a
group of experimental trials, and wasn't impressed with the need for all
the extra work. So I'm lazy.)
I know I haven't answered all the points brought up, possibly because I
don't think it's necessary, possibly because I don't know. I'd like to hear
other views. You may induce me to begin work on another article!
Sil Horwitz, FPSA
Technical Editor, PSA Journal
teched@psa-photo.org
silh@earthlink.net
Visit http://www.psa-photo.org/
Personal page: http://home.earthlink.net/~silh/
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