Until Reed sees your question:
Below are several time honored methods people use on rough-turned wood and green wood turned to size. This is assuming the blank is face turned and not end grain orientation.
Some people swear by or swear at certain methods. My own method is one of these. No sense in giving it since so many other methods work for other people. For everyone that says "this will work" there will be another who disagrees. Some say they have zero failures with their favorite method. Some accept a 20% loss. Rarely does anyone describe all the environmental conditions or even the type of wood or wall thickness they are turning.
If rough turning to thick walls to let dry then turn again to finished size, some ways people use that are successful:
- seal the entire outside with Anchorseal (basically an emulsified wax you paint on then let dry)
- seal just the end grain on the outside of the piece
- seal the entire bowl, inside and out - sometimes better for burls or wild grain.
- wrap the outside in plastic wrap. If too thick and warm and wet, this can cause mold.
- soak in denatured alcohol then dry
- put the roughed bowl in a paper bag or two and forget about if for a couple of months
- bury the rough bowl in a pile of wood shavings
- put it in a plastic bag. Every day, take it out, reverse the bag, and put it back in
- kiln dry the piece. Big productions turners like Glenn Lucas do this. Unless you are lucky this can be tricky since you have to control the heat and humidity according to a schedule.
- there may be more that I'm forgetting at the moment.
The idea is to slow down the drying. The faster it dries the faster it cracks, in general.
Moisture will go right through wax but slowly.
Melted wax is as good as anything but messy and extremely dangerous to melt if not done wisely. Nearly all wet tropical woods are immersed in hot wax.
With all of these, weigh the bowl regularly. When the weight quits changing it is dry enough to finish turn to final thickness.
If turning green wood to finished size, forget all of the above. Just turn it thin enough so the stresses from drying it won't cause cracks. No wax, plastic, or anything. The piece will warp.
For all of these it's best to have the wall thickness about the same all the way down and around the base. If the base is too thick the stresses due to shrinkage while drying can destroy the piece with cracks.
All of the above depends on the species of wood, the starting moisture content, and other factors such as the humidity and temperature and air currents in the drying place and the phase of the moon. Eastern red cedar, for example, will behave differently than walnut which will be different than red oak, etc. Too hot and too dry can be bad.
You might find the book "Turning Green Wood" interesting.
https://www.amazon.com/Turning-Green.../dp/1861080891
JKJ