Stains on architectural drawings

I am a paper conservator currently working the architectural
drawings of William Henry Playfair (1790-1875). Playfair was the
principal architect of the Scottish Enlightenment and came first to
notice in 1816 when he won the competition to complete Robert Adam's
unfinished buildings for Edinburgh University ( "The Old College").

Most of the drawings I am working on at the moment are from 1818/19
and are all watercolour and ink drawings on a fairly heavy
watercolour paper with little surface texture. On roughly 10-15 out
of 200 drawings I have noticed a peculiar oil(?) staining: The
stains have got a dark yellow/light brownish tint and look sometimes
a bit like spillage. In most instances, however, they look rather
like a greasy line following exactly the outlines of the drawing. On
two occasions I came across a nearly perfect imprint of someone's
palm--produced by the same kind of oily substance, I believe.

Now, I would like to know whether anyone has got any sort of
experience with architectural drawings of that particular period,
and whether you have encountered a similar kind of staining.

I was wondering whether architects in the early 19th century were
still producing their own tracing paper by saturating sheets of
paper with linseed(?) oil or similar. If they did, would it be
possible that by producing tracings from the original drawings, some
oil from the tracing paper could have transferred onto the originals
which would then have discoloured over the years leaving a dark
yellow mark ?

Susanne Ritgen
Paper Conservator
Edinburgh University Library
George Square
Edinburgh EH8 9LJ
Scotland

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                 Conservation DistList Instance 10:106
                  Distributed: Wednesday, June 4, 1997
                       Message Id: cdl-10-106-008
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