X-ray radiography

I have recently X-rayed 4 oil paintings on canvas. These landscapes
are dated to the latter half of the 17th century. In each case the X
radiograph shows quite strong lines of dense material across the
subject which I assume is caused by the uneven application of the
ground layer using a knife or similar tool. The alternative
suggestion has been that this might have something to do with the
glue lining although it's hard to see how glue of standard
composition could appear so dense. Has anyone come across this
feature in X-rays of other 17th century paintings?

Another strange feature in one of the paintings is present in some
trees outlined against the sky. In normal light these are dark
against the light tone of the sky. In X-ray the effect is reversed
and the trees appear light against a dark sky. Can anyone explain
this to me?

Kate Lowry
National Museum Wales
Cardiff UK


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                  Conservation DistList Instance 21:59
                   Distributed: Saturday, May 3, 2008
                       Message Id: cdl-21-59-018
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