How to dry bowls

From green blank to a bowl that stays round and whole.

Green wood shrinks as it dries, and it shrinks about twice as much along the growth rings as across them. A bowl turned to its final shape while wet will go oval, and a thick blank left to dry whole will usually crack. The usual answer is to turn twice: rough-turn the bowl while the wood is green, let the roughed-out bowl dry slowly, then turn it to its final shape.

1. Prepare the blank

Work as soon as you can after the tree is cut. Keep logs whole and the ends sealed until then.
Split the log through the middle and remove the pith (the soft centre). Bowls with the pith in them almost always crack.
Cut the blank round on the bandsaw and seal the end grain right away if you can't turn it the same day.

2. Rough-turn

Turn the outside and inside to roughly the final shape, with an even wall.
Leave the wall about 10 % of the diameter thick: around 25 mm (1″) for a 250 mm (10″) bowl. That leaves enough wood to turn it round again after it has warped.
Keep the wall even, including the bottom. A thick base and a thin rim dry at different speeds and crack.
Leave a tenon or recess so the bowl can be held again for the final turning.

3. Seal and dry slowly

Coat the end grain (the two areas on the side where you see the growth rings end-on) with end-grain sealer, wax emulsion or a thin coat of PVA glue. Some turners seal the whole outside.
Put the bowl in a paper bag, or a cardboard box with its own shavings, and keep it somewhere cool and out of sun, wind and heating. This slows the drying down so the outside doesn't dry much faster than the inside.
Turn the bag inside out or swap the shavings if they get damp, so mould doesn't start.
After a few weeks, when the weight is falling more slowly, the bowl can come out of the bag to finish drying in the open.

A common rule of thumb is about a month per 25 mm (1″) of wall thickness, but it depends a lot on the wood, the season and where you keep it. Weighing is more reliable than counting weeks.

4. Weigh until the weight stops dropping

Weigh the bowl right after rough-turning and write it on the bowl in pencil.
Weigh it again every week or so. A green bowl often loses a third of its weight or more.
When the weight has stayed the same for two or three weighings, the wood has reached the moisture of the room it's in, and it is ready for the final turning.
If you have a moisture meter: about 8–12 % for a bowl that will be used indoors.

This is what WoodDrying.net is for: register the bowl, add a weighing whenever you weigh it, and the chart shows when the line flattens out.

5. Final turning

The dry bowl will be oval. Mount it again, true up the tenon or recess, and turn it round to the final wall thickness. Then sand and finish as usual.

Other ways

Turn thin in one go. Turn the bowl to its final shape while green with a thin, even wall (around 5 mm). It dries in days and warps into an organic oval shape, often on purpose.
Soak in alcohol or dish soap. Some turners soak rough-turned bowls before drying to reduce cracking. Results vary by species.
Microwave. Short bursts on low power with cooling in between can dry a rough-turned bowl in a day or two. Weigh between rounds, and be careful: it can scorch or crack.

If it cracks

Small cracks often start at the rim or the end grain. Fill them with thin CA glue as soon as you see them, and slow the drying down (back in the bag, cooler spot). Mark the piece as failed in WoodDrying.net if it's beyond saving, so you can see later which woods and methods worked.