Sugar Maple on Sugar Maple base - March 18 - April 14, 2008 - 72.5 hours.
15.5 x 11 x 10 inches
I am frequently asked how to prevent wood from splitting. I first addressed that question on my "Frank Thoughts" page back in August of 2000. This page seems to be as good a place as any to post a more permanent discussion of the subject.
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 it 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. There is no permanent prevention for this natural phenemon short of replacing the water in the wood with some other substance that won't evaporate out. Doing such a thing is likely to affect the color and texture of the wood. The prevention I use for having 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 to split it lengthwise into at least half logs or maybe even quarter logs if that will still make reasonably large billets. Then as this wood dries further the outer edges can shrink around the axis of the center without producing many more cracks.
Determination was made from a quartered maple log. The right hand and the undetermined object 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.
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.
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