Saffola (pure safflower oil) or mineral oil were suggested in a naturalist site. I copied the information awhile back and can't locate the original site again, so am pasting the original text here, but if you are having difficulty with the wood drying out, stresses changing and cracks appearing, keeping a carving of green wood covered in plastic between carving sessions will prevent rapid drying and changes in stress. Splitting as the result of drying always starts from the outside of a log as the sapwood shrinks more than the heartwood. If you cannot work on your roughed out wood for a long period of time, submerge the carving in a bucket of water and add some bleach. The outer surface color will darken over time, but it can be removed with additional carving and sanding, because the wood will still have it's natural color under the surface. It will be odor free and with no cracks. When you're finished with your carving, apply a coating of Saffola (pure safflower oil) or mineral oil. If you have the time, it's best to seal the ends of the log and let it dry naturally until the wood has stabilized. This may take months to a year, depending on the type of wood and the climate.