I think grandpa was a frailer - which is just downpicking ususally one finger and thumb (often sone without the use of any pick) which would produce a mellow sound due to the playing style. Kyle Creed also produced a wonderful mellow sound on his homemade banjo, although he did use a metal pick on his index finger I believe. Chris Coole goes to the nail lady who puts on sturdy fake nails on index and second finger - which produce a fantastic mellow but clear tone on his open back Tubaphone banjo.