Corrosion

Various iron alloy objects in our collection have developed
particularly aggressive and unusual patches of corrosion. The
corrosion forms a pattern of concentric circles that appear to
radiate out from very definite central points (visually resembling
the pattern formed when a bacterial culture is grown on a petri dish
or that of growth rings in a tree trunk). I have removed the
corrosion products from one of the "patches" which reveals the
circular corrosion pattern deeply etched into the metal surface.

The corrosion patches have appeared on a number of un-related
objects so that it is unlikely that the corrosion is due to
inclusions in the metal; but the corrosion seems to radiate from a
central point indicating the possible presence of a catalyst. Has
anyone encountered this form of iron alloy corrosion before? Any
comments would be greatly appreciated.


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                  Conservation DistList Instance 16:42
                 Distributed: Friday, January 10, 2003
                       Message Id: cdl-16-42-015
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