Re: Adjacency Effects Again

From: Sandy King <sanking@clemson.edu>
Subject: Adjacency Effects Again
Date: Fri, 09 Apr 2004 10:41:54 -0400

I suffer from "darkroom affective disorder" and too much grape juice
from Andes (Mendoza, that is) today, but let's try...

> The literature on this subject appears somewhat contradictory.
> Richard Henry notes that since the creation of adjacency effects is
> via lateral diffusion the type of agitation should in principle not
> matter, and he observes that he obtained adjacency effects with very
> vigorous and constant agitation. Yet he notes that research quoted by
> Todd reached different conclusions on the importance of agitation.

Photographic materials and processing solutions have very large number
of variables, including ones that are not observable. Individual
scientific studies are usually limited to manipulation of one or two
variables at a time, because the parameter space grows unmanageably
rapidly as the dimension increases. When two or more variables are
manipulated, there may or may not be interactions between them. Some
of these are well studied, but many are not. Incidentally, advances in
knowledge of mechanism underlying development process give us a better
model as a framework to understand some of these interactions. But
these advances made in past few decades don't appear in darkroom
literature like those you consulted. So, pieces of data you see should
be interpreted as "one dimensional" or "all else being equal" deal
unless you try to work out the interactions of multiple variables...
So, the kinds of disagreements you pointed out look more like
oversimplifications to me.

Accutance enhancement depends on (1) inhibiting action of actively
developing area to the neighboring area of slow development; (2)
facilitating action of slowly developing area to the neighboring area
of active development; or (3) both. Major factors include:
concentration of developing agent(s), concentration of oxidized
developing agent(s), concentration of silver ions (which is influenced
by bromide and antifoggants), release of H+ or OH- during the course
of redox and further breakdown of developer oxidation products,
overall rate of development, and rate of diffusion. In relation to
adjacency effect, lateral diffusion is the mechanism by which the
influences of these factors reach the neighboring area, but agitation
can change many of these factors, so I would not say agitation is
irrelevant to adjacency effect.

> Also, some sources suggest that only metol based developers give
> adjacency effects

Metol has some advantage.

> since phenidone is highly resistant to the
> restraining action of bromide.

This is not very true. It's probably fair to say the induction time of
phenidone developers is probably less influenced by bromide
concentration than say metol or pyro-soda developers. But bromide
concentration is linked to silver ion activity and this influences the
other aspects of development.

Also, when people talk about phenidone developers, they often
implicitly assume hydroquinone is used. Phenidone-ascorbate developers
can provide sharper negatives but these are rarely discussed in
literature.

In tanning developers, catechol may not impair adjacency effect as
much because oxidized species are taken out of the equation by
engaging in tanning action without making too much of potent
developing species or sulfonate. But tanning developers are considered
unimportant in modern processing and I haven't seen scientific
research on this subject.

I can't think of good references on this topic right now. But key
results in mechanism and kinetics of development are important in
thinking about variables of development process. In that aspects,
papers by people like Pontinus, Willis, Turk, et al. published papers
on electrochemical aspects of development during 1970's.

--
Ryuji Suzuki
"All the truth in the world adds up to one big lie." (Bob Dylan 2000)