Edit: This is the process I use for once-turned bowls. You may need to modify it slightly for twice turned bowls due to the thicker walls.
I use the timed defrost setting.
- Weigh the bowl.
- Microwave 2 minutes on defrost.
- Turn the bowl over (not sure it matters) and defrost for 2 minutes again.
- Let the bowl sit for 1-2 hours.
- Weigh the bowl. You weigh after cooling, because the moisture gets pushed to the surface during MW. An hour or so of air drying gives you a better reading.
- If the bowl lost more than 3% weight, repeat 1-5. The 3% number is arbitrary and anecdotal but it provides a discussion point. If your bowl was 100 grams before drying, and 97 after drying one cycle, repeat steps 1-5. If your bowl only loses 1 gram the next cycle, you are done.
There are some other factors:
- Wood species and wall thickness. A very thin bowl, or one made of a wood known to move a lot, might need slower drying. It might be better to only MW for 1:30 at a time. If in doubt, slower is better.
- Weighing is better than using a moisture meter. I still use the moisture meter, but only to confirm what I already knew by weighing. A cheap gram scale is $15. (https://www.amazon.com/gp/product/B092W43Q25)
- I use my kitchen microwave. My wife doesn't love it, but she doesn't really complain. You may need to get a cheap used one for drying bowls. For the first couple of cycles, I wrap the bowl in a paper towel to catch moisture.
As always, your mileage may vary.