U of S | Mailing List Archive | alt-photo-process-l | Re: archivalness of gum

Re: archivalness of gum

My brain cells are completely stabilized with lots of spirits
but now you are testing how stabilized I am... Ok let's get

Water dispersible couplers are unlikely to be used today due
to their inferior color reproduction and difficulty of
synthesizing and purifying. These are surfactant-like bulky
molecules and they are pretty difficult to purify to the
usable degree. Difficulty in synthesis and purification is
directly reflected to the amount of resources and energy
wasted for the inefficient manufacturing, and I do not believe
that saving on the solvent in oil protect system would warrant
such a large offset. Oil soluble couplers, on the other hand,
are much easier to make and superior in color reproduction.

The mechanisms of dye deterioration vary. In older material,
magenta is most easily faded by light but not yellow and cyan,
which faded even in the dark via reduction or
hydrolysis. Therefore, the longevity of old color material
depends a lot on the storage temperature, humidity and light
exposure. Formaldehyde was used in the final bath to
inactivate unreacted magenta couplers, which can get oxidized
to cause stain and/or magenta fading.

Today's color material uses almost everything we can imagine
within practical limits to improve permanence. They have UV
barrier layer(s) and that's one of the reasons why magenta dye
lasts much longer today. (Another being improvement of the dye
coupler itself.) Emulsions also incorporate antioxidants that
slow down fading of the dye image. So, color material after
1980 went through several generations of improvements that
changed the relative weakness of each color image and the most
susceptible mode of threat to the image stability.

Some couplers are dispersed with new carrier material, such as
poly(acrylamide) and these tricks have improved the stability
(both in dark and light) of cyan couplers considerably.

In case of color material, residual bleach has a large impact
on the stability of the dyes. Modern color bleach baths are
formulated with some tricks to minimize this.

Residual thiosulfate in color film is usually not a problem
since fixing and washing are done at an elevated temperature,
and color fixer is usually neutral pH and does not contain
hardener. In old color material, if there is a significant
amount of residual thiosulfate, it may affect cyan image but
not magenta.

Surely some of these technologies can be applied backward to
the old Agfa system, if anyone is willing to make the Agfa
system again, and improve permanence over the old Agfa
system. But the water dispersible couplers themselves do not
make dyes that are as permanent as those from modern couplers,
and those couplers are not as efficient so that more silver,
more developing agent, and more couplers would have to be
used to make the image of same density range. Plus, like I
said earlier, making water dispersible couplers by inefficient
synthesis processes and purification would use more resources
and energy.

I must say that your old color material not experiencing much
color shift or fading is very lucky. I see some color slides
from 1960s in fairly good condition but they are dark stored
Kodachrome and they still have noticeable (but correctable)
color shift.

From: jfulton <jfulton@sfai.edu>
Subject: Re: archivalness of gum
Date: Fri, 21 Dec 2007 22:40:39 -0800

> In other words, the dyes formed could be destroyed through
> UV interactions (my presumption) . . . like today's sprays,
> which ward off UV destruction in digital prints . . . could
> be protected by a 'shield'. The 'shield' then was partially
> cleanliness via thorough washing and removal of chemicals of
> destruction like the thiosulfates, but it was also the
> formaldehyde, which hardened the dye cloud, protecting
> it. My theory, which seems to be substantiated due to the
> 1960's images being still here and with not bad color though
> kept in drawers, is that I used then a hypo-eliminator and
> washed twice as long and hardened w/formalin (which, oddly,
> I still have).