Armor

Fernando Lorenzo Gilabert <fergilabert [at] terra__es> writes

>I am working on a collection of XV century armours. Their surfaces
>are covered with a slight rust layer. The mechanical work under
>magnifying glass is effective but too slow. I tried, successfully,
>with a weak NaOH solution (in deionized water): the corrosion layer
>became soft and I could remove it with nonmetallic tools
>(toothpick).
>
>But, is it enough to wipe and remove with cotton swabs and ethanol
>to neutralize the NaOH action? Can the decorated areas (gilded) be
>affected?

While I am sure that your method is effective, and that it should be
possible to neutralize the NaOH solution after cleaning, I am wary
of using chemicals to remove corrosion products. I generally find
that treatments of this type produce a highly unsatisfactory surface
appearance.  I have worked on armor from several collections and
visited many more, and I can say that those armors cleaned
exclusively using mechanical methods preserve more surface detail
and have a more attractive appearance.  Admittedly, you do not
propose dunking an entire armor in acid, a method I have witnessed
the unfortunate results from more than once, but I am suspect of any
chemical cleaning for armor.  That said, it is true that mechanical
cleaning is time consuming and difficult.

However, NaOH is the prime ingredient in products such as oven
cleaner and is highly caustic.  Apart from any issues with health
and safety, my feeling is that even a dilute solution poses
potential long-term problems.  Even a small amount left in contact
and not neutralized will cause eventual damage, especially if
encapsulated by wax or lacquer.  Left exposed to air, sodium
hydroxide converts to other compounds (such as sodium carbonate),
but if coated it will remain active and corrosive under the coating.
Of course, without a coating, you end up back where you started-
cleaning off rust. So, though I am sure it means more work (doesn't
it always), I feel one should always avoid the use of the NaOH in
favor of the mechanical cleaning. Respectfully,

Edward A. Hunter
Assistant Conservator
Department of Arms and Armor
Metropolitan Museum of Art


                                  ***
                  Conservation DistList Instance 16:35
                 Distributed: Monday, November 25, 2002
                       Message Id: cdl-16-35-005
                                  ***