Pieces of glass in oil paint

I am currently working on a 17th century oil painting on canvas from
Urnes stavechurch in Norway. The artist is unknown, and it is likely
that the painting has been imported. The painting depicts the New
Jerusalem (also called the tabernacle of God/city of God) in an
almondshape circle. Surrounding the city are birds and plants.

The paint layer consists of a brownish ground, then a layer of lead
white and yellow (ocher), followed by a layer of small broken pieces
of glass. The glass is not mixed with the paint (as is clear from a
cross-section) but seems to be added at a later stage, possibly
while the paint is still wet. Consequently the layer of glass is
very fragile. Does anyone have some information on this kind of
painting technique? I am interested in any information on handling
and treatment of this kind of painting (personal experience or
bibliography).

Anne Apalnes Ornhoi
Paintings Conservator
The Norwegian Institute for Cultural Heritage Research/NIKU
PO Box 736 Sentrum
N-0105 Oslo
Norway


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                  Conservation DistList Instance 22:66
                   Distributed: Tuesday, May 12, 2009
                       Message Id: cdl-22-66-002
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