Wood slice ornaments, and why they crack.
Cut a branch into discs and hang them on the tree. Some of them will split open as they dry out, and the reason they split is the most useful thing about wood that anybody ever tells you.
- How long
- An hour of work, then two weeks of waiting.
- You need
- A branch · A fine-tooth saw · A drill · Sandpaper · String
- Messy
- A bit. Do it on a table.
Step 1. Find a branch between 40 and 60 mm across.
Thicker than a thumb, thinner than a wrist. A fallen one after a windy night is perfect and costs nothing. Straight is easier than curved. Birch gives you white bark and a pale face, cherry goes a deep red brown, and a knot in the middle of a slice is worth more than a clean one.
Step 2. Cut slices 8 to 10 mm thick.
Fine teeth, slow strokes, and let the saw do it. Clamp the branch or hold it in a vice. Nobody should be holding a round branch in one hand and a saw in the other.
Thinner than about 6 mm and the slice starts breaking along the rings while you are still cutting it. Thicker than about 12 mm and it stops looking like an ornament and starts looking like a coaster.
Step 3. Dry them slowly, in a paper bag.
Put the slices in a paper bag, fold the top over, and leave it somewhere cool for two weeks. Not a radiator. Not an airing cupboard. The bag slows the water coming out of the face of the slice so the whole disc dries at about the same rate.
Some of them will crack anyway. That is not you doing it wrong, and the next card explains exactly why.
Step 4. Drill the hanging hole 6 mm from the edge.
A 3 mm bit, straight through the face, with the center of the hole 6 mm in from the bark. Put a scrap of wood underneath so the bit breaks out into that instead of tearing the back of your slice. Closer than about 4 mm and the string tears out through the edge the first time somebody knocks the tree.
Step 5. Sand the face, leave the bark.
120 grit then 180, on the cut faces only, until the saw marks go. Leave the bark alone entirely. The bark is the reason this looks like a piece of a tree instead of a wooden disc, and it will come off by itself on the ones that were cut too late in the year.
Step 6. String them and hang them.
Garden twine, a loop, a knot. No varnish. Unfinished wood keeps the smell, and the smell is a large part of what you actually made.
Why the crack happens.
Wood is mostly water when it is alive. As it dries it shrinks, and here is the thing nobody expects: it does not shrink the same amount in every direction. It shrinks roughly twice as much going around the growth rings as it does going out from the center toward the bark.
Now look at your slice. The circumference is trying to get much shorter. The distance from the middle to the edge is only trying to get a bit shorter. Both of them cannot win, so the disc tears itself open in one place and every other part of it relaxes. One clean crack from the edge to the middle, and then it stops.
This is why a table top is never a single slice through a trunk, why a green log splits at the ends in the woodpile, and why the wood in a house that has stood for two hundred years is quiet and the wood in a house built last year is not. Once you have seen it happen to an ornament you will see it everywhere.
That is the end of this one
The word for what you just did is checking.
A crack that opens as wood dries, running from the outside in toward the center. It is not damage and it is not a defect in that tree. It is the only way a disc can stay in one piece while its outside gets shorter faster than its inside does.
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