All that is happening is that the wood is moving due to a gradient in
relative dryness from one area to the next. That is, you are exposing wood
that has been at varying distances from the previous outer edge or end of
the board, thus they are at, probably very minor, differences in moisture
content with the most moisture likely at the center of the board. Various
areas dry at various speeds and warping results. There are also different
stresses in even the cleanest og grained boards. Cutting the board alters
the stresses and warping results. Rough turn the platter and let it
acclimate. While I would leave a wet bowl for at least three months, a piece
such as this I would leave for 48 to 72 hours. Hope it helps.

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God bless and safe turning
Darrell Feltmate
Truro, NS Canada
www.aroundthewoods.com