Dear All, I have used two kinds of walnut (European and American black) for lute backs. It works as well as anything acoustically, so there's no reason not to use it. The density may be comparable to sycamore, but it is nowhere near as dense as birdseye maple. It is rather porous, but takes varnish well and is not (as far as I can see) oily. Both species have a tendency to be a cold brown, tending toward grey, but can be very attractive. One interesting feature I noticed - when ribs are bent with heat they tend to stay bent, unlike most timbers which usually have some tendency to unbend a little.
My most recent walnut lute was a 6c with holly spacers and a holly veneered neck - unfortunately the photos are on a disk I can't access at the moment but I will post them a.s.a.p. Best wishes, Martin To get on or off this list see list information at http://www.cs.dartmouth.edu/~wbc/lute-admin/index.html