Determination was made from a quartered maple log. The right hand and the crutch it holds came from the extreme inner portion of the original quarter section. The back of the figure follows the rounded outer edge of the original billet. There weren't any major cracks showing when I began carving, but this billet contained a hidden flaw often found in my cache of maple - an internal crack that didn't show on the outer surface. Most cracks begin on the outer perimeter of a billet and gradually grow inward with more drying. I think this particular hidden crack may have been caused by lightning or wind damage to the living tree before it was cut. I was able to obscure this crack with a crease in the shirt on the inner side of the right collar bone.

Wood Split Prevention

The Dogwood cross section shown below illustrates the simplest way wood splits as it dries and shrinks. A log doesn't just simply get smaller as it loses moisture. Rigid vessel and fiber walls, the grain of the wood, prevent it from losing hardly any length. Ray cells, a special type of rigid support tissue that grows outward from the center prevents it from losing hardly any girth. When a log is cut, the vessels, which in the live tree were taut with water traveling up from the roots to the leaves, gradually lose that water. The vessel walls then draw a little closer together. Something has to give. If the ray cells won't let things shrink toward the middle then the only thing left to do is to shrink sideways to a line running toward the middle (tangentially).

This will happen in nearly all cases to entire round logs no matter how carefully drying is controlled. The only permanent prevention for this natural phenomenon is to replace the water in the wood with a substance that won't evaporate out. My former sculpture teacher, Olen Bryant, gave me a gallon jar of an unidentified substance which was represented to him to work as a crack preventative. That jar is sitting on the shelf behind me on my page showing a wood carving holding block. Olen couldn't remember what it was called, but I think it must be polyethylene glycol. It has the color and texture of lard up to about 90° F., at which point it turns into a clear liquid. I have used it a few times on developing splits in ongoing carvings. It works in that it causes the developing cracks to close up, but if the wood it's applied to isn't later cut away, that area won't absorb whatever finish is applied to the completed carving, making it a slightly different color than the rest of the carving. Coating a developing split with some of the same surface protection that will be applied to the finished carving will help some and shouldn't cause any later problems with surface color unevenness.

It may also help some to apply clear varnish to the end grain of green logs stored for seasoning. Cracks usually begin on the ends of logs and at the outer perimeters, where open vessels are exposed like so many microscopic hose pipes. Varnish might help more if applied to the outer portion of the end grain only, because that will slow evaporation where it happens most rapidly.

My usual prevention for splits in wood carvings is to not use entire round logs for carving. The first thing I do to any new log I obtain is split it lengthwise into half logs or maybe even quarter logs if that will still make reasonably large billets. Then as this wood dries, the outer edges can shrink around the axis of the center without cracking.

More on wood split prevention

Any small split present on an unsealed wood block will get worse with a sudden, dramatic change from high to low humidity. This can happen if a wood block is brought from an outdoor location into a heated or air-conditioned house or if the weather changes to a dry pattern after a long period of wet weather. I work in an unheated shop and do not bring unfinished carvings into the house if the heat or air-conditioner is running, so artificial changes in humidity aren't a problem for me. Natural humidity changes are another matter. Spring 2003 was unusually cool and wet. Then the weather changed suddenly to a hot, dry pattern. Soon after this weather change, a split about a sixteenth inch wide opened up on my carving in progress where before there had been only a faint, almost invisible line. I was able to make this crack close back up by doing two things. First I put tung oil varnish on the surface that was splitting to prevent further rapid drying in that area. Then I drilled some large holes on the underside of the carving and expanded these holes with a chisel to a large hollow within the thick mass that was developing the split. This gave surface area for evaporative loss and shrinkage on the interior of the carving. Within a couple of hours the split had returned to being the faint, almost invisible line it was before. Now that the carving is completed and the entire surface is sealed with tung oil varnish it is no longer so adversely affected by humidity changes.

Bark left on or stripped?

It may seem logical to leave bark on logs while they're seasoning to slow the drying rate. Bark may indeed slow the drying rate some, but the most rapid drying is at log ends, where open vessels are exposed. Wood boring beetles are more apt to find places to lay eggs in bark than in exposed sap wood. Although bark peels off more easily from partially seasoned logs than from green logs, you may find that after seasoning wood with the bark on, you will have to cut away several inches of worm damaged sapwood. Worms are not as bad about penetrating heartwood because they are repelled by tannins, the waste products of trees, which build up in the heartwood. Sometimes worms are already present in living trees before they're cut, but most often worms get started while wood is in storage.

Crack patching

Having a split in a wood carving isn't the end of the world. Splits can be patched after they are completely done developing. If you are working with green wood, another split may develop beside your patch work later on. That's why it's better not to work with green wood. Before applying a patch, any split must first have straight, parallel edges so a well measured patch can be inserted. The tools required to make those edges straight and parallel vary infinitely, but often include a hand saw and or some files. You may email me for advice on specific problems or to add your own tip to this article. Five examples of my own crack patching can be seen on this page.

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