Re: Old Postcard Silver Patina

The silver mirroring is usually the result of the silver degradation
mechanism where the silver grain (like a very slow explosion) exploding
to elemental parts and this parts (eg.: silver ions) are slowly moving from
the original place so it become to noise from information.

Because that, the chemical reduction is usually not the best method: it
can lead to fog or/and a solarisation like phenomenon. So the remove of
silver tarnish can be better about picture quality. (Naturally there are
some risk with any invasive process on an old photograph.)

There is no known method to stop this deterioration process (as I
know) but to slowing it possible by optimal storage conditions.

You can read more about on these URL-s:

Jesper Stub Johnson: Chemical treatment of black-and-white
negatives, S. 191\u2013196 > pdf (7100 KB)
http://palimpsest.stanford.edu/iada/ta91_191.pdf

Klaus B. HENDRIKS: THE PRESERVATION AND
RESTORATION OF PHOTOGRAPHIC MATERIALS IN
ARCHIVES...Paris, January 1984 pp45-46.
http://unesdoc.unesco.org/images/0005/000586/058641e.pdf

Di Pietro, Giovanna Silver mirroring on silver gelatin glass
negatives Diss. phil.-nat., 2002 (2'134 KB)
http://www.unibas.ch/diss/2002/DissB_6232.pdf
http://sul-server-2.stanford.edu/byauth/dipietro/mirroring/

Bálint Flesch

http://archfoto.atspace.com/

>
> > It looks to me like typical "mirroring" from oxidation of
> > the image silver. The silver is converted to silver oxide by
> > polutants in the air. Some of this oxide migrates to the
> > surface of the emulsion and some is converted back to silver
> > by other polutants.
> * * *
> > There are ways of removing the silver and silver oxide
> > from the surface but they carry a risk of destroying the
> > original image and there will be some fading of the original
> > image beause some of the silver is gone.
>
> Some "aggressive conservators" have reported good results with
> bleach-and-redevelop protocols, but it takes fortitude to put a valuable
> old photo through that. I did it with a St. Ansel owned by a friend and we
> were both pleased with the results. It definitely eliminated the mirroring
> without losing density. YMMV.
>
Received on Fri Jan 6 09:18:38 2006