Iron objects with tin and gold inlays

In an excavation we carried out in the Netherlands, we have found
numerous small objects.  Although most of them were completely
covered with iron encrustations, they were recognized as belt
mounts.  This was confirmed by radiography: beautiful decorations
became visible on the fittings, buckles and buckle plates,  probably
dating from the 6th century AD.

Careful cleaning of one of the fittings under the microscope made
clear that we are dealing with iron plates with tin and gold
decorations.  The iron plates were attached to the belt with iron
rivets.  The decorations show animals and geometrical patterns.  The
iron, corroding away in favor of the other metals, grew out of the
plates and largely covered the surface.  Thus, not much metallic
iron remains in the plates (our cleaned one was completely hollow at
one side), but they are still magnetic.  We performed a qualitative
chloride test on the cleaned fitting which was positive, although
not very distinctive.

Now, we are in doubt: is it really necessary to desalinate the
mounts? The test was only hesitantly positive.  Because of the
fragile character of the inlays, we are worried if they will survive
the desalination baths.  During cleaning, parts of the deteriorated
tin inlays already came off the surface and the gold parts are made
of really thin gold foil.  What is wise to do? I have protected
non-ferro and wood parts during desalination with Paraloid B44 in
alkaline sulfite solutions before, but  I haven't worked with this
type of delicate inlays.

That's why I ask your professional advice; I can imagine that some
of you must have some experience with this sort of object.  Would
desalinate or not? If yes, how long (or short), and more important,
how to protect the inlays? If not, what to do to prevent iron
corrosion?

At the moment, the cleaned fitting is soaked in demineralised water
and tested for chlorides weekly.  This way, we will get rid of at
least some of the soluble chlorides before it is clear what will be
the rest of our treatment.  Any advice is very welcome.

drs. Karin A.N. Abelskamp-Boos
Conservation specialist
ADC ArcheoProjects
The Netherlands


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                  Conservation DistList Instance 26:39
                 Distributed: Monday, February 25, 2013
                       Message Id: cdl-26-39-022
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