Why has this little pot warped in this way?

[Cooper]

Why has this little pot warped in this way?
Yesterday I turned this little pot and lid from a piece of Bay, which I rescued from a shredder I happened to be passing, last summer. I expect when I turn something from green timber it to warp, which it has already. A gap of over 3mm has opened in line with the heart wood. I expected the shrinkage would be most pronounced furthest from the centre but the reverse has happened as in the little sketch. Is this because most of the heartwood has been hollowed out so it will shrink fastest and the sapwood of the sides and bottom has still got a lot of shrinking to do. (Sorry about the quality of the focus in the side view is so poor. I couldn't get the shadow to show properly with the flash.) P 5 was yesterday, P6 and P4 today.

I'm asking because if I true up the rims, so they are flat today, will I find in a month or so the the outer rings have shrunk and I will just have reversed the problem? I've made several little dishes from the same logs previously but never noticed the distortion to take this form but maybe I was just unobservant.

Thanks
Martin

 

[Chris152]

I stole this image off the net, maybe it helps in relation to the movement at the centre? I'd guess the centre of your Bay wasn't dry since last summer, and tension would have been released too?

 

[Cooper]

Thanks Chris, your diagram is exactly what I would expect but what the bowl seems to have done is the opposite shown in the heartwood section, i.e. the centre has contracted the most and the outer edge retained its thickness. Yes the wood was still very green, its such fun turning when its like that. The shavings just stream off!
Cheers
Martin

 

[Phil Pascoe]

I have seen skirting boards cup the opposite to the way you'd expect.