ive been doing some carving lately to make some basswood bowls. but all the wood ive used has ended up cracking as it dries. does anyone know a way to prevent this?
ive also been coal burning maple burls, these make awesome looking bowls that have a real cool primitive feel to them.
Don’t know about the cracking, though I assume certain types of wood are more or less prone. How do you get the maple burls off the tree?
i have to go looking for a long time before i find a suitable burl. most of the time im in some woods ive never been before and see a good one. then have to come back later and try to remember where it was i saw it. sometimes i find them where they have grown almost completely away from the tree. so the have a nice round shape that comes to a small circle where it connects to the tree. thats where i saw. its better to take them in the winter otherwise you chance killing the tree. in the winter the sap isnt running so it has a better chance to heal the wound.
The wood I harvested for making bowls, I let season for a year so it would dry out more naturally. My pieces were from a chopped down tree. I sealed the ends with paint so that it would not dry too quickly and crack.
When burning, don’t let the coals get too hot. They shouldn’t be hot enough that they are on fire. Extreme heat or cold will cause cracking.
When cracks develop don’t let coals get down in the cracks or it will keep growing. Instead, put sand down in there or burn around it until you can scrape off the cracked area.
My father does a lot of turning and carving. He uses paint to seal the ends of logs and other pieces of wood to allow them to dry more slowly (checking and cracking are a result of wood drying faster in some places than others - the dry areas contract, and the fibers pull apart). He also told me there are certain specialized sealants, etc. that are specifically made for drying timber like that, but a can of latex based paint will do fine. Red Oaks (the group, not the specific species) tend to check and split more severely during drying than most others because of the way the wood is made (e.g. the way the xylem is converted into wood).
I haven’t tried any burn bowls, myself, so I can’t really give any advice.
As an arborist, I can tell you that taking burls off of trees creates a wound that never heals - it just grows over. Compartmentalization within the tree through chemical secretions that fill the dead inner cells is usually what keeps a tree from rotting over a wound. It basically creates a chemical “wall” that stops decay at that point. Some trees are better and compartmentalizing than others. Hard maples are usually pretty good at it - softer “hardwoods” are usually bad. Burls on a tree are usually not bad for the tree in and of themselves - they’re basically an over-pumped dormant bud where the tissue just went kinda nuts. Usually it’s triggered by a fungal attack or some kind of insect infestation. Sometimes they just happen for little apparent reason.
Anyway - cutting off a burl leads to an open wound - so harvesting from live trees might be something you want to re-consider. Maybe consider just taking and using the tree in its entirety. It doesn’t matter what time of year you cut it off (with the exception of oaks and elms, but that’s because of Oak Wilt and Dutch Elm Disease more than anything). Additionally, a tree cannot “bleed to death” - they may lose vigor, and it might look extreme (especially on maples), but only in cases where a tree is already weakened (such as in a drought, or dealing with a fungal/insect infestation) will a tree lose so much sap that it will die. Most of the time what kills a tree is not the amount of sap it loses, but the amount of living tissue around the trunk it loses (which is why it’s bad to peel bark off of trees). I could on, but I think I’ve sounded enough like a botany text book for today. 
~ SW