Rust on outdoor steel sculpture

The answer by Jonathan Farley is a good description of one method of
preventing corrosion.  However given that the material is stainless
steel, simply cleaning it regularly may be an option depending on
the surface finish (polished or matt), the particular type of
stainless steel and the location of the statue, ie marine or
industrial or dusty. However, you will need to be more aggressive to
get rid of the present corrosion rust spots before you could revert
to a regular washing routine.

Properly cleaned stainless steel stays bright because of a very thin
film of protective chromium oxide (called a passive layer).  When
exposed to air without surface deposits (such as chlorides, iron or
mild steel particles, chemical fallout, dust, etc) this passive film
will keep the object bright. Some stainless steels (eg 316 or marine
grade) are more resistant to attack but all need to be at least rain
washed and, in severe atmospheric environments, washed with clean
(low conductivity) water possibly as often as every few months.

I have no idea what is in "Zud".  After fabrication, stainless
steels are usually treated with a pickling and passivating paste or
in an acid  bath.  The chemicals are strongly acid and while the
surface is left corrosion resistant, it will almost certainly loose
any  gloss it may have had.  The problem with the suggested coating
option is that stainless steel usually has pits under corrosion
spots and if these pits trap contaminants (salts and not just water)
then atmospheric moisture will be drawn through the coating and
regenerate the rust spots.

As you may gather, my background is corrosion rather than
conservation, so if you want amplification on the outline above,
please do not hesitate to contact me with a bit more detail of age,
weather conditions, etc.. Regards,

Graham Sussex

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                  Conservation DistList Instance 11:19
                  Distributed: Monday, August 25, 1997
                       Message Id: cdl-11-19-002
                                  ***