Relative stability of architectural blueprints and transparencies

Emily K. Bell <ebell [at] wellesley__edu> writes

>... 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.

Here at the Canadian Centre for Architecture we are sometimes faced
with same situation.  In fact, just last week our archivist decided
to deaccession a very large group of rolled transparencies on
plastic because they had been water damaged, were badly stained,
showed some image loss and were stuck together quite severely.  We
were able to determine that we do have a complete set of paper
versions of these--mostly diazotypes--so we will keep the paper
versions.

You are right that unless they are on a stable film the plastic
copies often don't do as well as paper.   Sometimes we see them
becoming extremely brittle, shrinking (and thus changing in scale
and becoming cockled) and offgassing.

We sometimes have several identical copies of a paper-based
architectural duplicate.  Then we will keep only one--the one that
is in the best condition--unless different copies have different
hand-written or drawn additions, which is often the case.

As for drawings on tracing paper, they are usually quite durable as
long as they are handled carefully--unless the tracing paper has
been made translucent by oil impregnation.  And an original
drawing--whether on tracing paper, drafting linen, or plastic
drafting film--is a priority for preservation.  Of course many
drawing on tracing paper have been poorly handled so will come to
the archive quite torn.  For researchers we may prepare these more
delicate ones in advance, unrolling them and covering them with a
sheet of mylar for the researcher's convenience and the protection
of the damaged paper.

Do you have a copy of Eleonore Kissel and Erin Vigneau's
"Architectural Photoreproductions:  A Manual for Identification and
Care"?   We follow their recommendations of separating the different
kinds of architectural reproductions from each other--either by
putting, for example, a whole group of blueprints in one folder and
a group of diazos in another, or at least by putting sheets of mylar
between the different types. It doesn't necessarily matter if the
people doing the rehousing know what kind of architectural
reproductions they are looking at--they simply have to recognize
that they are different from each other, and therefore should be
separated from each other.

As for storage conditions--ideally I think almost all of these
photoreproductions and transparencies would be better off in cold
storage and in well-ventilated containers.  You can tell by the
smells emanating from many of them that they contain chemicals that
may be causing their own degradation and that of objects nearby. But
the reality is that we don't *have* a cold storage big enough for
such large items, so we store all of ours in acid-free, neutral
housing (to avoid the risk of accidentally storing something that is
alkali-sensitive in a buffered folder), often stacked deeper than
we'd like to place them, at 20 deg. C and 40% RH.

Karen Potje
Chef, Conservation/Restauration
Head, Conservation/Preservation
Centre Canadien d'Architecture
1920, rue Baile
Montreal, Quebec
Canada H3H 2S6
514-939-7001 ext 1236


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                  Conservation DistList Instance 25:49
                   Distributed: Saturday, May 5, 2012
                       Message Id: cdl-25-49-004
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