Gunny and Keith are correct. I have had excellent success with a cotton ball wrapped in a piece of old T shirt. I use 192 proof alcohol, rub the stock down with a few drops of olive oil. I do not add any shellac but you sure could. The alcohol dissolves the old shellac, the oil keeps it from sticking. You are just following the same process as doing a French Polish finish. I have done several stocks that had a Shellac finish with great results.