Oh, It’s Drying Time Again…

Hewing a bowl with an axe and an adze certainly qualifies for what David Pye called “the workmanship of risk.”  The risk doesn’t end when the axe is laid down.  Anyone who is going to carve many bowls is sure to have some crack, but with a little foresight it shouldn’t occur often at all.  I’ve got another one ready to dry…

A couple days ago, I got around to hewing the 22″ x 17″ walnut bowl that I had laid out a while back.  In the photo above, it sits drying after the adze and axe work.  Inside it is a 7″ wide cherry bowl I just finished carving that gives a sense of scale.  That is all there is to my typical drying procedure.  I just sit it somewhere in the shop and check it out from time to time.  I have found that the most important steps to prevent cracking take place long before the carving begins.  Here’s my crack (and crying) prevention procedure.

Before carving:

• If I can’t use a log right away, I try to store it whole with the bark intact.  I paint all of the end grain with two heavy (slopped on) coats of leftover latex paint.  I keep the logs in the shade.  I’ve used them over a year later in some cases.
• When I’m ready to use a log, I start by cutting off a couple inches or so (depending on how bad the end checks might be) of the length from each end.  I study the end grain intently.  Any major checks may determine along what line I split the log in half.  Even the tightest, smallest checks have to be identified because the bowl will crack along these lines of weakness as it dries.  Sometimes small checks can be avoided without cutting away more log length by orienting the bowl in such a way that that area of the log will be carved away later.
• Once I am happy with the check situation, I split the log to make sure the pith, or center, of the tree will not be in the bowl.  Due to the differential between the amount wood shrinks along the growth rings compared to perpendicular to them (it shrinks much more along the growth rings, cracks usually project out from the pith.
• Due to this differential shrinkage, a bowl that is oriented in the traditional fashion (bark down) will develop some degree of crown across it’s top as it dries and the top width will increase slightly.  A bowl that is oriented bark-up will get slightly less arched and the sides will get a little closer to each other.  For us carvers, this is no problem at all — let it move, and our tools freely follow the new shape (still symmetrical usually) as we make our final cuts after drying.
• Some woods and conditions are more prone to cracking.  There are lots of charts available that show the percent of shrinkage of various wood species, but there are many other factors such as the moisture content when harvested or a tree growing under tension on a hillside.  I’ve learned a lot just by trying lots of woods and scenarios, but I still get surprised, and not always pleasantly.

During Carving:

• If I have to pause midway during the green carving stage, I always keep the piece in a plastic bag.  I don’t want any drying to occur until enough mass has been removed from the log so that it can move as it dries without cracking.
• Bulky areas are prone to problems.  I think of it this way: even with the pith gone, a half-log will still crack on the ends because the ends are losing moisture much faster than the interior.  When we carve a bowl, we reduce this differential greatly.  If we get rid of enough bulk, then the moisture can escape more evenly and the bowl can move freely as it dries.
• I try to make sure the thickness of various parts of the bowl are symmetrical, so that both sides move in the same way and dry at the same rate.  Hands and eyes do the job.

After Carving:

• I am in no hurry to dry a bowl, but I have found that drying too slowly (buried in wet chips, plastic bag rotation, etc.) can often result in mold or stains that go too deep to be removed in the final carving stage.
• I will often rub a bar of paraffin wax across the handle ends before setting the bowl aside for drying.
• I consider weather, humidity, and other conditions that might impact drying.  If I lived in Arizona, I might have to adjust my procedures!  Absolutely, I keep a drying bowl away from wind.
• If I am concerned that a bowl may dry too fast and crack, I will slow it down through a variety of methods.  Sometimes just letting it dry while sitting on top of fresh chips is enough.  Some other methods I have used successfully are burying the bowl in dry shavings, drying in a paper bag, and wrapping it like a mummy in an old bed sheet. This last one I tried recently, and it worked well.  The drying is regular, but slowed.
• You can check if a bowl has dried completely by weighing it on a kitchen scale over successive days.  When it stops losing weight, that’s as far as it will go under those conditions.  I usually just go by feel to know when I will do the final carving. Sometimes this is after two weeks of drying, often longer.  I’ll definitely wait longer before hand planing the bottom flat.
• A couple weeks in with no cracks and you’re home free.  No worries after that.

Although I rarely have a bowl crack during drying now, it is the nature of this workmanship of risk.  And besides, it may be an opportunity to try something creative:

(Apologies to Buck Owens and Ray Charles for the title of this post!)