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Subject: Pink fingerprints on photographic print

Pink fingerprints on photographic print

From: Giovanna DiPietro <dipietro<-a>
Date: Friday, August 26, 2005
Tim Vitale <tjvitale [at] ix__netcom__com> writes

>I have seen a few pink fingerprints on B&W prints before, but I've
>never had to define the source.

I have never seen such color in the fingerprint, but, back at the
time of my PhD on silver mirroring, I examined lots and lots of
mirrored photographs. I noticed that the color of "silver
mirroring"can range from blue to bronze, green and violet. Silver
mirroring is silver sulphide (Ag2S) but the size and shape of the
mirroring particles can vary a lot. I took TEM micrographs of bronze
and blue looking silver mirroring and observed that in the bronze
areas the particles were bigger and  more distant from each other.
In the blue areas, the particles were smaller and very close to each
other, forming almost a continuous film.

There are different mathematical models to predict the color of a
layer of particles in gelatin. One generally has to know the index
of refraction of the particles (therefore the chemical composition)
and also the size, shape and average distance of the particles. If
the particles are very close to each other, it is possible to
successfully predict the color by assuming they are a continuous
film. If they are spaced apart, it is necessary to consider the
scattering of light of each particle and, possibly, the interference
of the light scattered by each particle. A continuous layer of Ag2S
particles gives rise to a bluish color but I do not know how it
would be for a continuous layer of AgCl (or any other compound)
particles .

Giovanna Di Pietro, PhD
Institute for the Conservation of Monuments
Research group for Conservation Science and Technology
Swiss Federal Institute of Technology Zurich
ETH Honggerberg, HIL D 33
8093 Zurich
+41 1 633 63 03
Fax: +41 1 633 11 60

                  Conservation DistList Instance 19:11
                  Distributed: Friday, August 26, 2005
                       Message Id: cdl-19-11-002
Received on Friday, 26 August, 2005

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