Wood contains moisture in two places - the lumens, and
on the cell walls. The first is called unbound, the second bound water. There are no ruptured cell walls with boiling for a number of reasons, chief among them being holes in walls to transfer water and nutrients laterally, second, no cytoplasm within the cells far beyond the living cells in the primary xylem. Folks boil the wood, and might get some benefit from the softening of the lignin, relieving some growth tension in nasty grain. Price is muddying the color a lot. Your walnut shimmers with secondary colors when air-cured, but is pretty universally brown when steamed in the kiln. Same thing. However, you can't get more water onto the cell walls than the fiber saturation level, so you're not hurting drying much there. When the unbound water's evaporated, and the bound water begins to, the wood shrinks. That's where the problems start. Idea is to smooth the transition from high relative humidity and saturation to low relative humidity and equilibrium with its environment come into play.
We can create a controllable minienvironment by bagging, the most common method of slowing evaporation. Bag, box, big container of similar moisture "Kiln" regulated to remove water slow enough to equalize through the wood but rapidly enough to keep it from molding.
We can coat the outside of our bowl with things that attract and hold water to keep them from checking. Liquid Dish Detergent - glycerol - is popular and pretty effective for the price. Bigger alcohols like PolyEthelene Glycol up to 1000, a solid at room temperature, both blocks the pores and attracts moisture, and is very effective. Ethyl/methyl alcohol -"DNA"- evaporates faster than water, and is therefore of no use. One I'm particularly fond of in the water-loving group, is potato starch. Rub into endgrain, like the Swedish spoon carvers.
We also use fully occlusive coatings like water emulsion wax Acrylics, or even latex paint. All more or less effective at slowing the loss, combining, to some degree, elements of the containment and expansion approaches..
But, the best thing to do is to realize that water moves through the tree through the endgrain, and is lost at up to a dozen times faster through it than through quarter, , or maybe 10 times faster than face grain, Turning to uniform thickness means nearly nothing, since it's the orientation of the grain which determines rate of loss, not thickness. Don't make a bowl too broad or flat in the bottom. Almost assured of trouble as the wood contracts, trying to make a smaller circle, and may overstress. If you need one like that, go to a surface dressing an mild containment.
All you want to bone up on - prepaid
https://www.fpl.fs.fed.us/products/publications/specific_pub.php?posting_id=18102&header_id=p
Specifically on wood structure
https://www.fpl.fs.fed.us/products/publications/specific_pub.php?posting_id=17963&header_id=p
Or how water is held and lost
https://www.fpl.fs.fed.us/products/publications/specific_pub.php?posting_id=17964&header_id=p
EDITED BY MODERATOR TO REMOVE SNARKY COMMENT TOWARDS OTHER MEMBERS. IF YOU CAN'T BE CIVIL THEN TROLL SOMEWHERE ELSE.