Turning green/wet walnut

[Leo Van Der Loo]

An explanation, very technical is here about how wood dries and why it will split doing this, the bottom part with red lines around give you the short reason it splits.
how wood dries and why it can split doing so.jpg

This gives you the brown paper bag working as a in effect a unheated kiln drying rough turned bowl blanks.
Drying rough turned blanks.jpg

[Olaf Vogel]

I have green wood drying success to vary from from tree to tree.

For my money and effort, the easiest is to slather a wax sealer on the wood after roughing it down. Pay special attention to the rim end grain.

When the wood is critical, I'll apply wax for a couple days in a row to the entire bowl. It's not the quickest solution, but for me, it's the easiest. It works *almost* all of the time with any kind of wood.

Oh yeah, you aren't working near the pith are you?

This is the cheapest, easiest and most successful solution I have found.
Additionally, I dry them in my cold cellar to slow down the process.

And I always try leave the pith in - more visual interest and I do a lot of end grain bowls.