I was given an old mystery fiddle a few days ago. I think it can be made playable again. The fingerboard is kind of grimey, so the first thing I want to do is clean that off. I was planning to start with a damp cloth. Is there something else I might want to try?
Since it's an old fiddle, you could also check for any 'grooves' worn in by the strings while at it...
Recently luthier showed me the grooves in my fingerboard and said he wanted to 'dress' it and I was bit skeptical, but I let him do it... neck feels smooth as silk and so easy to play, afterward! It did make a significant difference in feel and playability.
Given that it’s an old instrument, it’s quite likely that the fingerboard desperately needs to be planed. Have a luthier check it out, then you don’t have to mess with it and risk damaging the instrument with solvents yourself.
I watched a video earlier this year put out by Kennedy Violins in which they showed their process for cleaning. When it came to the fingerboard they used distilled white vinegar applied to a cloth. It works very well.