Identifying early 20th century map

I am currently working on a map, most likely made in the early
1920s, paper on canvas, measuring approx 1x2m. The map depicts the
urban structure of the town of Mytilene, Greece and is drawn on a
scale 1:2000. This particular map seems to be the key that connects
the several hand-drawn town maps which were drawn on a scale 1:500.
For a more thorough view and description of one of the 1:500 maps of
this series please check

    <URL:http://www.euromed2010.eu/e-proceedings/content/full/193.pdf>

I am finding it difficult to identify how the 1:2000 map was created
and what materials and techniques were used to make it. The map is
drawn in reddish-orange, on a black background (cleaning with water
does not remove the black colour).  This means that although maps
are usually drawn in black ink on a white sheet of paper (such as
the 1:500 maps of the 1920s series), the 1920s 1:2000 map is the
exact opposite: the lines, letters, North Arrow etc, are in reddish
orange, and what should be a white background is actually black. It
gives the impression of a negative, without however being a negative
image, as all the words on it can perfectly be read.

Has anyone ever encountered such an object? Meaning, a map drawn in
red on a black background? Why would they make a map on a black
background? Could that be some kind of a reproduction technique? And
how was that done? What methods would you suggest for cleaning? Any
idea on what the reddish-orange substance used to draw its elements
is? Whom should I contact for further information? If anyone can
help, I would be more than happy to send close-ups by e-mail.

Evangelia Kyriazi
BA Hons Conservation and Restoration
MSc Geography and Applied Geoniformatics
Laboratory Associate of the Technological Institution of the Ionian
    Islands
Department of Protection and Maintenance of Cultural Heritage


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                  Conservation DistList Instance 25:37
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