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EARLY / LATE GROWTH ("GROWTH RINGS")
use of tree growth rings to date historical events
I can no longer find it, but I used to have a cartoon which used tree growth rings to illustrate irony. It showed an incredibly old redwood tree, cut down, with some of the rings labled, much as in the picture above. The very last ring was labled "The year Ronald Regan was elected as the "Environmental President' "
Douglas fir planks, showing very strong difference between light-colored early growth and darker-colored late growth. Many trees exhibit strong growth ring patterns, and that's what makes for the big difference in grain pattern among cutting techniques (flat cut, quartersawn, rift cut, rotary cut, and so forth). Few trees have quite as stark a contrast in both color and density between early and late growth as Douglas fir, which is why I've chosen it for this example.
The separation between early and late growth can be anything from the very sharp line of Douglas fir to a very indistinct separation where the two merge together almost impreceptably. The relative thickness of early/late growth will also vary substantially, although the late grown is invariably thinner than the early growth. In some woods the late growth is a very thin line compared to a very broad early growth.
other examples of growth rings, weak and strong
Just in case you're interested, the woods shown above are: afrormosia, two samples of ash, bloodwood, cypress, guarea, genuine mahogany, philippine mahogany, hard maple, meranti, obeche, osage orange, pau amerello, two samples of pine, teak, and black walnut.
A coat rack made with Douglas fir over red oak. I have exploited the fact that the late growth is very much harder than the early growth. The piece was burned with a torch then scrubbed with a wire brush. The soft early growth just turned to ash and scrubbed right off whereas the hard late growth scortched but did not burn and did not scrub off, thus giving a nice ridged effect and a highlighted grain contrast. If you enlarge the detailed pic, you really see the 3D effect my process created. Finish is polyurethane.