Removing stains from gold

Anil Dwivedi <anildwivedi7<-at->gmail<.>com> writes

>Gold acid purity test has badly stained a gold ornament.  Please give
>some suggestion so that the stain can be removed from the gold
>article.

If you have any details of what was applied to the object that would
help.  Any information on the composition of the gold alloy, or the
type of object would also help.

I suspect that the acid applied in the test may have stripped away
base metals in the gold alloy.  This could have left copper or other
corrosion products on the surface.  Unfortunately, even if you
polish off the corrosion, the composition of the alloy underneath
may have been changed enough to permanently alter the colour of the
gold.  If only the surface of the gold is affected, a heavy
polishing might wear through to unaltered gold, but this would be a
harsh treatment and would not be recommended.

If the gold was a thin plating, the acid could have affected the
alloy underneath, making it easier for the plating to flake off.
This damage would be permanent.

Another possibility is that the gold is actually silver with a layer
of shellac on top to make it look gold.  If the shellac coating has
been damaged, this will also alter the colour.  In this case, you
might be able to inpaint the colour loss.  In all cases though, the
acid test is likely to have permanently altered the surface in a way
that cannot be reversed.  My recommendation would be to make sure
any acid residues are gone and the surface is clean.  Other than
that, I would probably leave it and just be satisfied with being
wiser about the use of destructive testing methods.  This is the
reason such tests are done on inconspicuous areas on the back of
objects.

I hope this is of some help,

Valerie Tomlinson
Conservator
Auckland War Memorial Museum
Tamaki Paenga Hira
The Domain
Private Bag 92018
Victoria Street West
Auckland 1142
New Zealand
+64 9 306 7070 ext 7304


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                  Conservation DistList Instance 28:48
                   Distributed: Friday, May 15, 2015
                       Message Id: cdl-28-48-001
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