Mystery substance or process on paper

We have been unsuccessful at identifying the source of a mysterious
smoky and darkened appearance on some paper objects, related colored
drawings and engravings that were (a) archival communication from
the artist to the engraver and printer, and (b) part of a
distribution process for communication to other collectors of bird
specimens,

The darkening may be described either as an incredibly fine
particulate deposit (not visible under 40x microscope and not
particularly mobile with cotton or other surface cleaning material);
or a color change of some adsorbed material; or change in the
cellulose due to either preceding case.

No significant result was detected with XRF when comparing untouched
background paper to the darkened background area.  We hope that your
wide variety of experience and many eyes can help us recognize and
identify the culprit.  A possible clue is in the masked appearance
of some of the central images.  We have some guesses as to inventive
unorthodox processes, but your thoughts will be appreciated, and
hopefully will result in a fruitful discussion archived in the
comment thread to the blog post:

    <URL:http://siarchives.si.edu/blog/mystery-diagnosis-and-case-unidentified-bird-shadows>

Please enjoy reading Kirsten Tyree's post, and viewing the pictures
in the embedded Flickr set.  The images may all be clicked on
independently to view them high resolution.

Looking forward to hearing from you,

Nora Lockshin
Paper Conservator
Smithsonian Center for Archives Conservation
Smithsonian Institution Archives
Capital Gallery, Suite 3000, MRC 507
202-633-5913
Fax: 202-633-5927


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                  Conservation DistList Instance 27:31
                Distributed: Thursday, February 6, 2014
                       Message Id: cdl-27-31-026
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