Glass beaded coin purse

Amanda Pagliarino <amanda.pagliarino [at] qag__qld__gov__au> writes

>A glass beaded coin purse (1800's) in our collection smells
>distinctly 'vinegar-like'. ...

The strong vinegar smells suggests that the object has components
made of cellulose acetate.  I have analyzed hundreds of beads on
ethnographic objects in museum collections by nondestructive
infrared reflectance spectroscopy using a portable IR spectrometer
with a fiber optic probe.  These beads were variously described as,
and looked like, glass, pearl, shell, mineral, plastic, and metal.
However, in many cases, in spite of their appearance, they were made
of cellulose nitrate, cellulose acetate, cellulose butyrate,
polystyrene, and other plastics, that very closely imitated the
appearance of the other materials.

Metal beads on the purse are described as quite corroded on their
upper surfaces and the corrosion tested positive for carbonates (but
the method of test was not stated).  It is possible the so-called
glass beads on the purse are cellulose acetate that has degraded to
produce acetic acid, which smells like vinegar (hence the name
"vinegar syndrome" attached to the deterioration of cellulose
acetate photographic film).  Acetic acid attacks metals to produce
metal acetate corrosion products.  Metal acetates react with
atmospheric carbon dioxide to produce metal carbonates.  Thus the
carbonate detected in the purse bead corrosion products may be from
this reaction.  Acetates may also be present.

The deteriorating beads are described as "fragile and tend to
separate and chip, and show fracture lines within their structure".
This description could just as easily apply to cellulose acetate
beads as to glass beads.

If the beads are not made of cellulose acetate, then maybe some
other component of the purse, such as the handle, clasps, etc. may
be made of cellulose acetate and contributing the acetic acid.  It
is possible for a cellulose acetate object to appear to be in good
shape, but still be producing acetic acid.

R. Scott Williams
Senior Conservation Scientist (Chemist)
Conservation Processes and Materials Research
Canadian Conservation Institute


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                  Conservation DistList Instance 15:38
                Distributed: Tuesday, November 20, 2001
                       Message Id: cdl-15-38-003
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