I put it on the end grain. Put on 2 layers. If you've already cut it into a bowl blank to be safe cover all but the bark. I still lose some with the end grain sealer but it helps a lot.
I prefer parrafin wax for saving blanks. If I've cut it into a bowl blank and plan to save it for a longer time I cover all but the bark with wax. If I think I'll get to it fairly soon I cover just the end grain portions. If it's in log form I coat the ends with wax. I do this with the wax in an electric skillet. If you leave the pith in you still stand a good chance of losing it. Keep your eyes on it and when it starts to check cut it up and do something with it. If you can't turn it cut it into squares such as 4x4, 3x3, etc as long as the log. Coat the ends with wax and put them up to dry. I've saved a lot of wood this way.