RE: Old Postcard Silver Patina

Thanks Liam and all who replied. Some very interesting info.

~m

-----Original Message-----
From: Liam Lawless [mailto:liam.lawless@blueyonder.co.uk]
Sent: Friday, January 06, 2006 12:41 PM
To: alt-photo-process-l@sask.usask.ca
Subject: RE: Old Postcard Silver Patina

Here's something from an oldish book, Restoration and Photographic Copying,
Alexander Shafran, Amphoto, 1967. He's talking about rephotographing an
oxidised original, but I did once clean a mirrored print with household
ammonia and recall that it worked OK.

Liam

Exudation

Another phenomenon that occurs to old photographs should be mentioned here.
This is a peculiar one, to which the name "exudation" has been given. What
occurs is that minute metallic specks form on the surface of the old
photograph. This is due to the oxidation of the silver compounds in the
emulsion that form the picture. These specks act as miniature reflecting
surfaces that prevent our seeing the image clearly. Sometimes they are only
visible when the picture is viewed from a side angle. However, these
reflections are picked up by the copy lights and cause a glare effect that
prevents our obtaining a good copy negative of the picture image. The
negative records only the glare and not the picture that lies beneath the
layer of metallic grain.

Fortunately, these granules are on the surface of the picture and can be
removed without destroying or damaging the underlying image. They can be
removed in much the same manner as that used for the removal of dirt and
grime. That is, the layer of grain can be removed by rubbing it off with a
kneaded or Artgum eraser, or it may be washed off with a cotton swab
moistened with liquid soap or a mild solution of ammonia.

Unless the original is a small one, the use of the moistened cotton will
prove much more practical than the use of erasers. Here, too, the same care
and caution must be exercised as with the removal of dirt and grime. The
original can be coated with a layer of dirt as well as that of the exuded
silver grain. The same cleaning process will take care of both layers; it
may only require a little more effort and time.

When the surface of the original, or that part of the original we want to
copy, is in otherwise perfect condition-without cracks, damage, or dirt-the
exudation effect can also be reduced or removed by the application of a thin
coating of petroleum jelly. It acts to add a gloss to the print surface on
which the reflecting grains are lost. The petroleum jelly should be rubbed
on sparingly. If too much is used it will streak, and these streaks will be
reflected as white lines on the copy negative. This method is practical only
when the original is a small one and where there is absolutely no dirt
present.

-----Original Message-----
From: fb [mailto:aikus2@freestart.hu]
Sent: 06 January 2006 11:46
To: alt-photo-process-l@sask.usask.ca
Subject: 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 17:30:14 2006