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PAINTING MATERIALS

Species of woods differ considerably in the ratio of their radial and tangential
shrinkages on drying. In the case of mahogany, birch, and black walnut, these
differences are relatively slight, and hence these woods are not prone to crack
extensively on drying. On the other hand, the differences between the radial and
tangential shrinkages of beech, maple, and oak are large and these woods crack

FIGURE 5. Relations of quarter-sawed and plain-sawed boards, adapted from figure I,
page 8, a drawing in 'The Identification of Furniture Woods/ Miscellaneous Circular
no. 66 (Washington, D. C.: Government Printing Office, 1926), by Arthur Koehler. At
the left is a quarter-sawed (radial) board; in the center the log with annual rings showing
at the end grain; and at the right a plain-sawed (tangential) board.
radially on drying. Since wood shrinks more tangentially than radially, quarter-
sawed lumber shrinks less in width and more in thickness than plain-sawed lum-
ber. When pieces of quarter-sawed and plain-sawed lumber are placed edge to
edge in the same panel, one may become thinner than the other with change in
moisture content* Plain-sawed lumber, also, has a tendency to cup, since the
center side is more nearly radially cut than the outside. A. Koehler (' Shrinking
and Swelling of Wood,' pp. 18-20) has published tables giving figures which permit
the comparison of radial and tangential shrinkages of a great many species of
wood. Werthan and Haslam have shown that the expansion of summer-wood
is often greater than the over-all expansion of the wood. Their data indicate that