A friend of mine asked me to clean 2 old Colt revolvers for him. They both have walnut grips with the colt medallion embedded in them. The grips are very dirty and show signs of wear, but do not appear to be cracked or chipped. So, my question is, what's the best way to clean the wood and get the dirt out of the checkered grooves and the Colt medallion? Without doing any harm? Should I put a coat of finish on them?