Dear list members, thanks to all those who answered my question about cleaning lute soundboards. I will consider to use one of the recommended techniques. I was also not talking about slightly signs of aging but rather about the extremely dirty lutes one can often find. In my experience, many lutes are in a condition (as far as dirt is concerned) that most other instrumentalist would not tolerate. And non-lutenist friends of mine were often irritated when seeing the dirty soundboards of lutes of even well known professional players. And personally, I would like to prove that I have been practising through my playing skills rather than the dirt on my lute.
Best wishes, Stefan Ecke