Don't Turn It
Apprenticeship Day 23
So I'm back in the barren wastelands of the north. I was supposed to be here a week ago, but got struck down with flu. Better late than never.
As usual, Monday started with the weekly business meeting. I got brought up to speed on what went on during the holidays, and during last week. Woodspirit Handcraft had the bowl and cup sale. Last week, before sending all the packages out, Jarrod and Jasmine lined up all the bowls and spent some time comparing them. Jarrod let me know that I missed out, it sounded like a great way to dig deep into the minutiae of bowl design. Seeing how a smaller or larger foot changes things, the difference of the same shape being taller or shorter, and so on.
This week, we'll be mainly working on lidded boxes. On February 1st there'll be a box sale and the opportunity to put your name down for a lamhog. To get me back in the swing of things, Jarrod suggested I turn a few bowls for myself this week. I had the inner nested bowl waiting for me in the freezer and Jarrod thought there was another bowl blank outside the basement window.
So I started on my little bowl. I was pleasantly surprised to find that I hadn't completely forgotten everything. Starting work with what is essentially an already roughed out bowl is a nice and easy reentry to turning. With the bowl being so small, it didn't take me too long to finish.
I couldn't find the mystical bowl blank Jarrod thought was outside. So I went to my favourite of activities: mandrel turning. An apprentice turner can't have too many mandrels. Plus with piles of boxes on the horizon, we need more with a smaller diameter. Having to be accurate to a 1/32 of an inch is a challenge, but a good lesson in tool control. I only swore a little bit when the tool dug-in while working on the tenon.
After lunch Jarrod walked me through his process of selected and chainsawing wood for lidded boxes. It's important to have the grain run straight through the box, running as parallel as possible. Straight grain throughout will help ensure that the wood shrinks evenly, with as little warpage as possible. To help achieve this, relatively small boxes have to be turned from quite large diameter wood. So Jarrod was ripping a 26" silver maple log into small boards for boxes that might end up with a diameter of just 4-5". We also cut up some birch for bowl blanks.
Back in the workshop, Jarrod showed me how to bandsaw out blanks for box bases and lids. I spent a while making four sets of those. Then I spent the rest of the afternoon turning another bowl nest. I only had time to do the outer bowl, so I'll try and finish the inner bowl tomorrow.
Okay, haven't yet mentioned why the title is harping on about mushrooms. During the morning meeting, we were talking about me prepping lamhog blanks. I've done the axe work on a whole bunch of these, many of which are in a bin bag in the basement freezer. Unfortunately, most, if not all, will have to go. We've had some issue with wood vessels cracking. Partly it's been due to the low humidity of winter, partly due to some funky wood. There was a whole batch of bowls that had an inner section of heartwood that was darker than the stuff around it. That extra dark heartwood split on all the bowls that had it. Fortunately the checks seemed limited to that discoloured area of the heartwood. Clearly the wood was compromised in some way.
So here's a little bit of science about wood and rot:
Lignin is the material that makes wood woody. Tree cells have a tough secondary wall that adds itself to the inner surface of the more flimsy primary wall. This rigid cell wall is mainly cellulose, which trees create through the sugars produced during photosynthesis. About 25% of wood is tough lignin.
When wood is left sitting outside, especially in direct contact with the ground, agents of decay start to do their work. Mainly fungi, these fantastic organisms make sure that the world isn't littered with the remains of dead plants and animals. When fungi gets into wood, it's first noticeable by the way it discolours and stains the wood. Certain kinds of early stage 'incipient decay' is sometimes referred to as spalting. The discolouration can occur without significant loss of strength in the wood. The fungi has gotten into the wood cells and is feasting upon any stored material inside the cell. Eventually though, the fungi will start to attack the cell walls themselves.
There are two main kinds of wood rot: Brown rot and white rot. Brown mainly eats away at cellulose, while white rot attacks lignin as well as cellulose. Catch white rot at the right time, and the attractive dark brown or blank zone lines are what we refer to as spalted wood.
Once you dry out a piece of wood that has begun to rot the fungi can't develop any further. Taking the wood down to below 20% moisture content halts the decay process. Properly cared for wood will last indefinitely without further decay.
Some of the wood that we had used for lamhog blanks came from birch that had been sitting in Jarrod's woodpile for a while. An informal test of how far along the decay process a piece of wood is to try and dig your thumbnail into it. If you can easily mark it with your nail, the strength has been compromised. This doesn't mean it's unusable. If you were making spoons it might be okay, but you'd need to leave it thicker to compensate for the weaker wood.
This wood seemed to pass the thumbnail test. It wasn't soft or punky. It did however smell slightly of mushrooms. Jarrod and I have had several conversations trying to figure out why certain items crack or check when others don't. Especially pieces made from wood that isn't obviously compromised. Our current theory is that the birch used for the cups which cracked was under attack from some sort of white rot. The lignin was being eaten away.
The issue with using this compromised wood for cups is that filling them with liquids causes the wood to move. The wood isn't wet long enough for fungi to start it's work again, but the liquid seeps into the wood cells, causing them to swell. The previous work of the fungi has eaten away at the lignin in the cell wall, potentially warping their shape when they fill with water. This tiny movement is enough for split to eventually form.
The only clue that the wood might have been weakened was the mushroom smell. So we're going to have to go through the freezer and pull out cup, mug and lamhog blanks that have been compromised. We might repurpose them into spoon blanks, or just dry them out and stick them in the wood stove. Fortunately Jarrod has recently purchased some veneer quality logs, so all future cups will be turned from that.