Tom,
I cut a bunch of 90 degree oysters from a piece of 5" walnut about 10 years ago. I sliced it rather heavy--about 1/16", put newspaper between the pieces and sandwiched them between two pieces of ply. I changed the newspaper daily until it no longer felt damp. Then I wrapped stretch wrap around it and set it aside to wait for the right project (which never came). The last time I looked, there is some radial checking, but at the pith not at the sap and the pieces are distorted like potato chips. If I ever do want to use them, I'll have to treat them to get them to lay flat. There is some useful information on pp 82 and 83 of Pierre Ramond's book on Marquetry.