Plastic drafting tools

I am a museum technician working for the National Park Service at
the Frederick Law Olmsted National Historic Site, in Brookline, MA.
The site is dedicated in part to Olmsted's legacy as one of the
fathers of landscape architecture.  Recently, we discovered in our
collection some historic clear plastic drafting tools that had begun
to deteriorate. The majority of them simply smell bad, something
akin to old cheese or an acidic vomit-like smell.  Most of them are
also brittle and have cracks and fractures. A few of them are badly
crazed and fragile, and crumble into tiny pieces if not handled
carefully; several were found completely degraded.  We soon began to
suspect that these tools were made with cellulose nitrate or
cellulose acetate.

The tools are primarily 30 60 90 degree triangles, 45 45 90 degree
triangles, French curves, ship's curves, and various drawing
templates (circles, squares, letters...).  Most of them are from
identifiable brands such as Kueffel and Esser, Dietzgen, Berol
Rapidesign, and Frost and Adams (a few tools retain no means to
identify their manufacturer). Most of the tools have identification
numbers for the specific style of tool within the brand name's line
of drafting tools.  With this information in hand, I have contacted
most of these companies in an attempt to discern what material these
tools were manufactured with.

I have been able to trace the Kueffel and Esser tools back to the
turn of the century, and it seems certain that these tools were made
with cellulose nitrate.  Dietzgen no longer carries any of the
shapes or styles that we have, and no one there seems to know what
type of plastic they may have used years ago. However, in a sales
catalog dated 1956, Dietzgen refers to a new plastic they use which
is "resistant to burning".  This may indicate that they had
previously used cellulose-based plastics.  The Frost and Adams
company went out of business sometime in the 1940's. The Berol
Rapidesign brand seems to be much more recent, perhaps dating to the
1960's at the earliest, and the company still manufactures nearly
identical templates today.  According the  company, they use
Butyrate plastic.  Regardless, the items made by Berol Rapidesign,
although they have deformed and cracked from improper storage, do
not appear to have any inherent vice (yet).

My question to the distribution list is; assuming that many of these
are cellulose-based plastics, what is the best procedure to follow
to conserve or preserve these items?  So far we are favoring
freezing them in our cellulose nitrate film freezers, at
approximately 22 below zero.  Can anyone recommend written sources
or individuals we can consult for advice?  The AIC referral service
has referred us to Clifford Craine and Lisa Mibach.

Tom Braun, Preservation Technician
Frederick Law Olmsted National Historic Site
99 Warren Street
Brookline, MA 02146

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                  Conservation DistList Instance 9:35
                 Distributed: Monday, October 16, 1995
                        Message Id: cdl-9-35-002
                                  ***