Permanence of RC papers

Darius Himes <dhimes<-a t->midas< . >bwc< . >org> writes

> I am currently researching the longevity of resin-coated
> photographic papers. Can anyone suggest any publications dealing
> with this topic, and also in relation to the longevity, in an
> archival environment, of traditional fiber-based photographic
> papers, such as those currently on the market (Ilford Multigrade,
> Brilliant, Cachet, etc.)? With many thanks,

The short answer is that there really hasn't been anything written.
Part of the problem is that papers have changed quite a bit in the
past several years. We also tend to find, at least within the
industry, that there are two schools of thought. One is that if you
store the material properly there is no problem. The other side says
that many places can't store them properly and therefore must take
other action.

RC has had a number of problems in the past including
polyethylene/emulsion cracking, silver image deterioration, and
staining from oxidized, migrated, incorporated developers. The
industry has tried to address these problems as best as it could.
With the incorporated developers for example, many companies have
added anti-oxidants into the paper (which is sandwiched between the
two layers of polyethylene) and into emulsions. Some companies are
doing away with incorporated developers altogether (except in those
papers that absolutely must have them (that is, rapid access machine
processable papers.)

If asked what I would chose for archival use, I would recommend a
fiber base paper over RC. At the very least, there seems to be a
benefit to having a porous support. It is thought that air
pollutants entering a fiber base paper seem to be able to escape to
the paper support and away from the emulsion making the photograph a
little less susceptible to oxidation damage. In an RC base,
migration of pollutants through the polyethylene is very slow so the
pollutants tend to stay in the emulsion where they can attack the
silver. As far as I know, no one has proven this, but it seems to be
the reigning theory within the research field. In addition, there is
still question about the titanium dioxide in the base. It is the
best whitener for this paper, but in the presence of UV light, it
forms a singlet oxygen which was responsible for both the cracking
and silver deterioration problems. The industry has addressed this
problem by adding anti-oxidants mainly. (UV absorbers must be used
carefully otherwise you eliminate the benefits of optical
brighteners -- although optical brighteners in themselves act as a
UV protectant too.)

This has helped the problem greatly. In general, there is little
concern with the cracking problems now. (Although preservatives
don't last forever. Even a Twinkie won't last forever.) It is
possible that with infinite money, the industry could make papers
even more stable. However, the industry (or at least a few of the
companies I know) have determined that people just aren't willing to
pay very much of a premium for very much greater stability than is
currently available. It makes no sense to spend a lot of money on
research if the general market doesn't really care.

As for the silver image? Silver is not as noble as most people
think. For some reason people accept having to polish the silverware
(and other such things) and yet still expect the photographic silver
to last at least for hundreds of years. If anything, the
photographic silver is in such small pieces that it's surface to
volume ratio makes it significantly more vulnerable than a silver
platter or tea set. *ANY* black-and-white, silver based image (not
including thermally processed) that you want to last must be post
treated in sulfur, platinum, gold, or selenium to form more stable
compounds. This includes negatives (which people tend to forget) and
even motion picture film. It is the only way (unless you can ensure
that the air in the storage environment will always be relatively
dry and free of all oxidants.) With films, the images don't tend to
change in tone very easily and therefore it tends to be easy to
recommend any of the above treatments. Most of them require high
levels of conversion for adequate protection. Photographic prints,
however, tend to change in tone very easily and the only
recommendation that can be made is to try different combinations of
paper and stabilizers until one is found that provides both a
pleasing image tone and good protection.

As a side note, I might add that long washes with fiber base papers
can result in uneven removal of the optical brighteners. In the
worst cases, you may see yellowish streaks. It isn't yellow. What
you're seeing is the natural white of the paper and baryta. The
yellowness is caused because the optical brighteners in the other
areas make the the rest of the image look so white and bright that
white is no longer perceived as white.

In summary:

    1.  Process in accordance with the manufacturers instructions.
        (Test your hypo or use fresh. Wash well, but don't over do
        it.)

    2.  Post-treat in sulfur, selenium, gold or platinum.

    3.  Store in accordance with national or international standards
        (or at least do the best you can.)

-Douglas Nishimura
Image Permanence Institute

                                  ***
                  Conservation DistList Instance 11:28
                Distributed: Tuesday, September 23, 1997
                       Message Id: cdl-11-28-005
                                  ***