Conservation of archaeological composite object

Robert Lodge <mckaylodge [at] aol__com> writes

>In Cons DistList 15:31, Karin Abelskamp inquired about alternative
>methods not involving heating for removing chlorides from a Roman
>iron/wood composite object.  This is not my field of expertise.
>However, a product common in the realm of industrial protective
>coatings that I have used to remove surface-reacted-surface-attached
>chlorides (and sulfates) from steel prior to coating is Chlor-rid.
>It bonds with the ions and rinses free with water.  No residues are
>left according to independent testing.  For information on the
>product, how it works, test kits, and a brief on salts contamination
>go to <URL:http://www.chlor-rid.com/>.  Perhaps it will be useful for
>the iron.

I would be concerned about using the product (Chlor-rid) mentioned
below on archaeological iron.  The Chlor-rid company notes (please
see their web page) that their product is intended to remove soluble
salts from surfaces to improve the bonding of surface treatments.
Soluble chlorides on the surface of archaeological iron would be
removed by almost any washing method commonly applied (eg, alkaline
soaks, soxhlet extraction), but the longer term problem is the
chlorides loosely bound in the corrosion products themselves.  I
don't know how effective Chlor-rid would be in reducing or
solubilizing these minerals, or in penetrating the micro cracks and
pores where the chloride corrosion cycle typically takes place.

In response to Ms Abelskamp's original question about the iron/wood
composite object, the typical treatments for waterlogged wood and
chloride contaminated iron are not compatible. While it is possible
to treat wood and iron together, both components usually suffer some
degradation from the other's treatment (e.g., high pH baths will
degrade the wood, and PEG is corrosive to iron), and neither
treatment is ever completely satisfactory. So if the object can be
disassembled (and reassembled again after treatment) without loss of
it's archaeological significance, I would do so, and treat the
components separately.

Howard Wellman
Maryland Archaeological Conservation Laboratory


                                  ***
                  Conservation DistList Instance 15:33
                 Distributed: Friday, October 19, 2001
                       Message Id: cdl-15-33-002
                                  ***