Tracing paper

I am a postgraduate student at the University of Northumbria,
studying the conservation of fine art on paper.  I am doing research
into transparent papers and architectural drawings.  I was recently
given a sample roll of tracing paper.  The roll was tightly rolled
and had discoloured to a bright yellow.  The person who gave me the
roll said that this discolouration occurred quite often when the
rolls were exposed to the sun, she did not however have any
information about the manufacturer or retailer, as it was about
fifteen years old.

A sample of the "yellowed" roll was put it in a Melinex sleeve
(sealed on 2 sides) and placed in a plan chest drawer over night, by
the following afternoon, the paper had returned to its original
colour showing no trace of yellow.  Another sample separated from
the roll reverted to its original colour as I was looking at it.

The samples do not fluoresce under UV and do not revert to the
yellow when exposed to daylight.  There is also an acetic type smell
in the middle of the roll.

Has anyone had any experience with this before, or know why it
occurs?  I suspect it is as a result of the manufacture of the
paper.  Any information at all would be appreciated,

Alexandra Greathead
University of Northumbria
Burt Hall
Newcastle upon Tyne NE1 8ST

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                  Conservation DistList Instance 12:72
                   Distributed: Monday, March 8, 1999
                       Message Id: cdl-12-72-007
                                  ***