Kinda depends on time of the year they are harvested. When I harvest in the spring, you can hit the bark with a hammer, and it will break the soft growing layer. The bark will come off in chunks. I got a bunch of elm burl once, just too many for all that hitting. I bought a mini jack hammer from Harbor Freight. I cut the point off the chisel so I had a 1" dia hammer. It worked great. I then pressure washed them to really clean them up. Fall harvest is really tough. If I'm turning a bowl, I leave the bark on till I get close to the final size. Then it usually peels off. If you want pen blanks, cut them close to size and with less area, the bark should peel off too.
