Iron cannons

I am seeking information to help me to determine the right
conservation treatments for over hundred iron cannons that are
located outdoors around Suomenlinna fortress

    <URL:http://en.wikipedia.org/wiki/Suomenlinna>

Most of them are from 18th century but there are also cannons from
19th and 20th centuries. Some of them have been painted, but there
is no record left how it has been done.

The treatments should be planned taking into consideration the
northern climate by the Baltic Sea. We have four seasons with sun,
rain, wind, snow and wet snow. Temperature varies from up to +30
deg. in summer to occasional low of -30 deg. in winter. The cannons
can also be freely accessed by the visitors and many climb over them
and unfortunately, they are also damaged on purpose. Also we don't
have a laboratory at the Suomenlinna and therefore I do not have any
equipment and chemicals at the moment.

The two major problems are vandalism (graffiti made by spray can
paint and scratches on the surface) and active corrosion. Active
corrosion is partly breaking pieces off from the cannons and it
occurs on surfaces that has been scratched.

What have you found to be a good method to remove graffiti, without
harming the metal? Also experiences of removal of active corrosion
are welcome--corrosion inhibitors used, any experiences of Can Trust
or Tannic Acid treatment? (As I understand, they change the colour
of the surface and the tannic film is not so stable). What kind of
protective coating would be preferable after the treatments? Should
I consider any anti-graffiti coating? Are there any for these
conditions?

I would appreciate it if someone could help me. I have read several
articles but I am not sure how the treatments would work for these
cannons as we have such extreme climatic variations. Also there are
such a large number of cannons and the treatments have to be
performed outdoors where the cannons are located.

Noora Hirvonen
Student of Conservation of Cultural Historic Objects
+358 50 5874033
Fleminginkatu 15 A 30
00500 Helsinki
Finland


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                  Conservation DistList Instance 21:4
                   Distributed: Friday, May 11, 2007
                        Message Id: cdl-21-4-026
                                  ***