I wood say that all "natural" wood(s) darken over time, finished by whatever method. OIL type finishes seem to age quicker than say urathane, stained or not. I think this is caused by oxidation / UV degration, of course dirt, sweat and oil etc. certainly darken wood but I've refinished stocks that are "clean" but once touched by sandpaper a fine darker layer is removed and a lighter colour comes to the surface. This is one reason if I can get away with removing old finish with a stripper and steel wool thats the way I go, it all depends on the situation. JMHO - FWIW --- John Can.
