I finished off the silver birch goblet I started turning from green wood a little while ago. It's been sitting in my hot water cupboard since then, which was sufficient to dry out the thin shell of the bowl, and the surface of the thicker stem.
It did not go entirely smoothly. In the course of drying out, it bowed very slightly, which made it very difficult to remount on the lathe to turn true. Unfortunately I'd already turned the shell down quite thin, and truing it up on the lathe made it thinner still.
Never mind, lesson learned for next time.