Gold leaf

Lynn Campbell <campbelll [at] ccc__govt__nz> writes

>I have a query regarding gold leaf on a painting.  Our gallery has
>just purchased a painting done in 1996 supposedly painted with gold
>leaf. There is a significant amount of discolouration taking place.
>Upon enquiring from the artist whether it was really gold leaf we
>were told it was definitely real gold leaf.

Sounds to me as if this was bronze powder paint or perhaps Dutch
Metal Leaf.  Can you see joints where the leaves come together??

One can test for gold non-destructively with x-ray fluorescence.
This requires having an XRF set-up where the art work can be put in
the correct relationship to the x-ray beam and detector.  You might
find one in a university lab., in a forensics lab., or in customs
laboratories.

One can also remove with a hypodermic needle or a small scalpel a
tiny flake (too small to see) of the "gold" from the edge and
perform chemical microscopy on it.  It it's gold, it won't dissolve
in HCl or conc. ammonia.

Touchstone tests are reliable, if you can rub enough off the surface
to make a streak.

If one could collect enough of the deterioration product, one could
do x-ray diffraction on it--I bet it's copper oxide.

At which point one can start to think about what to do.  Perhaps
alkaline rochelle salt could be used to remove the copper (II)
deterioration products without damaging the paper, followed by very
thorough washing.  Other pigments will be a problem; watch out for
Prussian blue! Acidic methods are probably contraindicated.  You've
got a real problem here.  Repainting the background or commissioning
a replacement work come to mind.

                                  ***
                  Conservation DistList Instance 10:16
                 Distributed: Wednesday, August 7, 1996
                       Message Id: cdl-10-16-003
                                  ***