I'm new to hollow forms. I've done about 10 so far with good success. These two failed on me yesterday after a few days of drying in a paper bag - my standard process for drying green single turned items. Walls are 1/4", opening is 1 1/2" and they're about 8 1/2" tall. I wouldn't win any contests on wall thickness consistency all the way to the bottom but in looking at my previous ones that warped but didn't crack I made the neck thickness thinner, around the inside curve and further down the wall. In all I've read here (lots of good info) it seems 3/16 or even less is the magic thickness to shoot for when turning green. I'm assuming wall thickness and bad luck caught me on these two (pecan and elm). Going to let them finish their dance on splits and cracks and then decide if a colored epoxy fill is worth the effort. I'm not a fan of epoxy fills that are noticeable and only use it clear to fill in small knots where it blends in, but rarely. That said, on "artsy" pieces I know it's a different approach so might be something to consider.