Just wanted to add my voice in asking archaeologists and conservators to
avoid high temperature treatments on iron. These treatments, which involve
heating objects for several hours to temperatures of +350 C in an
oxygen-free atmosphere, have been described in the conservation literature
and have generated a lot of discussion. To get an idea of some of the
concerns, refer to papers in "Conservation of Iron" edited by R.W.Clarke
and S. M. Blackshaw, Maritime Monographs and Reports No. 53 - 1982,
National Maritime Museum, Greenwich.  To the best of my knowledge, heat
treatments to extract chloride from  iron  have not been used in Canada or
the US. If I am mistaken, please let me know.  Many years ago (late
1970's/early 80's) conservators at Parks Canada and CCI toyed with the idea
and rejected it based on the reasons that Chris Salter gave - loss of
information about the manufacture and history of the objects.
  At CCI we are continuing research into aqueous treatments for iron, but
are also looking at preventive conservation methods. "Preventive"
conservation  is defined as "All actions taken to retard deterioration and
prevent damage to cultural property through the provision of optimal
conditions of storage, use and handling"  (IIC-CG Code of Ethics and
Guidance for Practise, 1989).  For archaeological iron, preventive
conservation means recording by radiography and keeping the objects in the
best possible storage conditions ( low humidity and clean). An example of
preventive conservation is to ensure that metal objects do not touch each
other in their storage container. Not rocket science, but sometimes common
sense is not obvious.
   One project which CCI will be carrying out is  the practical application
of shrink-wrapping collections of archaeological iron - both treated and
untreated objects. This would reduce the dust and dirt levels in iron
storage areas, reduce the risk of metal-to-metal contact in storage, and if
the artifacts go ahead and corrode, the bits would be kept together in
their plastic package.  Conservators at the National Museum in Denmark have
been vacuum packing iron since the late 1980's with good results (Jensen et
al, "From a waterlogged site to the archaeologist's desk - new packing
methods with a minimum of handling", Archaeological Conservation and its
Consequences; Preprints of the IIC Copenhagen Congress, 1996, pp. 89-93).
Seems like a practical approach when artifacts have to be stored whether or
not they go through a treatment.    One factor we would be looking at is
the amount of heat involved in shrink-wrapping, ie: if this would affect
metal structure, given the short duration of time (much shorter than
heating objects to get a wax coating applied).
 
Judy Logan
Senior Conservator, Archaeology
Conservation Processes and Materials Research
Canadian Conservation Institute
1030 Innes Road
Ottawa ON
K1A 0M5
tel: 613 998-3721    fax: 613 998-4721   e-mail: [log in to unmask]