a couple ways i've done it, a bowl is scooped out with a curved knife(like a crooked knife) and with gouge chisels
when green wood this works pretty well, though tools must be sharp. If green, the burl is kept in a paper bag when not carving.
When its dry, its obvioulsy tougher to work, you can burn out the interior , and then cut away the char...
or
the fastest way : there is a great little burr tool to fix on a highspeed dremel. looks like a spiked ball and it chews away rough wood quickly
it's a fantastic little time saver
