Relative stability of architectural blueprints and transparencies

The Wellesley College Archives have a large collection of
architectural plans, dating as far back as the founding of the
college in the 1870's, in several formats (blueprints, images on
coated fabric, "vellum" and tracing paper, clear plastic film -
possibly Mylar).  In some cases there are multiple copies of the
same image, in different formats, and the question has been raised
whether it is necessary to keep many different copies if, all else
being equal, some of them will last better than others.  Partially
this is a question of archival philosophy, and I am not an archivist
who will be making the final decision, but the aspect of the
question that I have been asked to help with is whether some types
of architectural images are more stable over the long term than
others.  I am familiar with the light sensitivity of blueprints, but
beyond that is the paper itself likely to be more durable than the
transparent or translucent drawings used to make the blueprints?
These are often on very thin tracing paper, or as-yet-unidentified
plastic films.  To me it seems that if the film is Mylar or another
stable polyester or polyethylene film, then it will last very well,
whereas if it is PVC or some other unstable film we might be better
off focusing our efforts on preserving the blueprint copy instead.
When it comes to the tracing paper versions, I don't have an
intuitive sense beyond the fact that the thinness of the paper makes
it seem less durable to me. Can anyone recommend any references that
discuss the history of these types of drawings and images, and in
particular how they behave over time? Has this kind of question come
up for anyone else?  If we do end up keeping multiple copies in
different formats, the next questions will likely center around
whether different formats require different storage strategies, so
references dealing with that kind of decision would also be welcome.

Emily K. Bell
Collections Conservator
Margaret Clapp Library
Wellesley College
106 Central Street
Wellesley, MA 02481-8203
781-283-3595
Fax: 781-283-3690


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                  Conservation DistList Instance 25:48
                  Distributed: Friday, April 27, 2012
                       Message Id: cdl-25-48-016
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