Cleaning metal

Melissa Marsh Heaver <mmheaver [at] aol__com> writes

>In my spare time, I am on the Vestry of my local church. We have a
>nickel and silver alloy cross, c. 1957, that hangs from the ceiling.
> ...
>
>It has been taken down for Lent, and stored. We hope to have it
>cleaned and probably relacquered, as it hasn't been down in at least
>15 years. The local person the church wants to do the job is
>suggesting that it be cleaned via "sand-blasting", but with glass
>beads. Is this a wise idea, or will we be removing metal? If this
>method isn't a good idea, is there anything else we can use to clean
>it and get the grunge off?

Using glass bead blasting to clean metal will remove metal albeit
far less than using sand blasting *but* what may be more important
is the fact that on a microscopic level, the glass beads will be
plastically deforming the surface of the metal and putting tensile
stress into the surfaces. This stress can cause the straight pieces
to bend or twist thus causing the visualness of the object to be
affected. Additionally, this stress coupled with any residual stress
within the sculpture could cause a metallurgical failure over a long
period of time.

There are much safer ways to clean this object but they will most
likely take a longer time to do and be more expensive. I will let
others more versed in cleaning these two metals make suggestions.

Regards,

Jim Moss


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                  Conservation DistList Instance 17:63
                  Distributed: Tuesday, March 30, 2004
                       Message Id: cdl-17-63-004
                                  ***