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    Understanding Figure in Wood

    continued

    Figure arises from the visual variabilities of normal wood structure, namely growth rings and rays. The more uneven the grain and the larger and more conspicuous the rays, the more distinctive the figure.

    In quartersawn lumber or quarter-sliced veneer, the plane of the major cut is more or less 90 degrees to the growth rings. Depending on the longtitudinal variation of the grain, the figure will be a parallel-line pattern on the face of the board.

    The distinctive appearance of the rays, which is known as ray fleck, may vary from the intricate cross-striping of cherry to the large, showy and lustrous rays of oak, known as silver grain. To reduce the size of the ray flecks and yet produce an interesting pattern, woods such as lacewood and oak are sometimes cut just off the true radial in order to produce rift-cut or rift-sawn surfaces.

    Variability through Cutting

    If a log were a perfect cylinder with uniformly thick growth layers, the figure on the surfaces of boards cut in tangential planes would be parallel markings. Fortunately, every tree grows with enough irregularity to distort the otherwise static markings. On flat-sawn surfaces, then, the growth rings intercept the surface obliquely, forming ellipses or U-shaped or V-shaped markings down through the area of closest tangent to the rings.

    Toward the edges of a flat-sawn board, depending on how wide the board is and how much curvature is in the growth rings, the figure approaches edge grain. Where growth rings are fluted slightly, as in butternut, basswood, and sometimes black walnut, an irregular but interesting figure results.

    Rotary veneer cutting produces a continuous, repetitively merging series of tangential figure. Cone cutting, which is a method of removing a circular bevel layer of veneer analogous to sharpening a pencil, produces interesting circular pieces bearing cone figure.

    Variability through Tree Form

    The grain direction (that is, the direction of the longitudinal cells) of the average tree trunk is more or less straight, with some normal variation from strict geometric form. Wood from other parts of normal trees may exhibit interesting figure resulting from grain distortion.

    Crotches, for example, where a somewhat equal forking of the trunk has occurred, develop an unusually twisted and intergrown structure where the two stems merge. A cut passing through the center of the crotch produces feather crotch figure. If the cut is toward the outside of the crotch, a swirl crotch figure results. The term moonshine crotch is also applied to crotch figure. The stump region of the tree also produces interesting figure.

    In some species, other deviation from normal structure may occur, either as a common feature or as a rare exception, which produces interesting and attractive figure in the wood.

    Curly figure results when longitudinal cell structure forms wavy or curly grain. A split radial surface looks like a washboard. When this surface is smoothly machined to a flat plane, a cross-barred effect is produced by the variable light reflection of the cell structure intersecting the surface at various angles. In maple this is termed tiger maple, or fiddleback, because it is preferred for violin backs. Some of the most remarkable pieces of curly figure can be seen in old Kentucky long-rifle stocks.

    Ribbon or stripe figure is produced when wood that has interlocked grain is cut radially. Interlocked grain is the result of repeated cycles of spiral growth, varying back and forth from left- to right-hand spirals. Except for short pieces, such wood is virtually impossible to split. These reversing spirals create a characteristic visual effect, due in part to the variation in the length of the severed vessels at the surface.

    The lines are long where the grain direction is parallel to the surface but reduced nearly to pore diameter where the vessels intersect the surface at a considerable angle. The varying light reflectiveness of the fiber tissue also contributes to the overall appearance.

    Figure that shows short stripes is often called roe figure and the interlocked grain referred to as roey grain. Where wavy grain occurs in combination with interlocked grain so the ribbon figure is interrupted at intervals, the figure is termed broken stripe; when curly figure predominates, a mottled figure results.   >>>

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    ArchWeek Image

    Lacewood with ray fleck figure. This piece was rift-cut just off the true radial to produce interesting figure while reducing the size of the flecks.
    Photo: Randy O'Rourke

    ArchWeek Image

    Flat-sawn figure is characterized by oval, U-shaped, and V-shaped patterns. Boards (left to right) are ash, cherry, southern yellow pine, chestnut, white birch, and eastern spruce.
    Photo: R. Bruce Hoadley

    ArchWeek Image

    The jagged contours of the butternut come from fluted growth rings.
    Photo: Randy O'Rourke

    ArchWeek Image

    The continuous tangential figure of Douglas-fir plywood is typical of rotary-cut veneer.
    Photo: Randy O'Rourke

    ArchWeek Image

    Crotch-figure in mahogany.
    Photo: R. Bruce Hoadley

    ArchWeek Image

    Curly figure results when longitudinal cell structure forms a wavy pattern. When the wood is split, a washboard surface results. Curly figure is most pronounced when cut radially, as in this sugar maple.
    Photo: Randy O'Rourke

    ArchWeek Image

    The curly figure in this red maple board is produced largely by the changing angle of light reflection.
    Photo: Randy O'Rourke

    ArchWeek Image

    If spiral grain in a tree cycles one way and then the other; interlocked grain results. If a log from such a tree were turned down on a lathe, the reversing angle of the spiral grain would result as shown.
    Photo: R. Bruce Hoadley

     

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