UNITED STATES DEPARTMENT OF AGRICULTURE
FOREST PRODUCTS LABORATORY
MADISON 5. WISCONSIN L L A' l
I i .V r -OA7
COLOR TESTS FOR DIFFERENIA 9G-HEARTWOOD
AND SAPWOOD OF CERTAIN 1OAKS, uigi aEbORY
Three chemical color tests have been developed by which sapwood and
heartwoodof certain oaks, pines, and Douglas-fir can be readily differ-
entiated. They consist of the application of a small amount of chemical
solution across the grain of the wood. The chemical used depends upon
the kind of wood to be tested.
Test for Oaks
Two chemical solutions can be used to distinguish heartwood from sap-
wood in oak. One is Taylor' s concentrated Benzo Yellow pH indicator,
a chemical used for making acidity tests. Its reaction to the more acid
heartwood and to the less acid sapwood produces the characteristic color
differentiation. The heartwood stains red and the sapwood yellow. A
minute or longer may be required for the full development of color.
Occasionally the red heartwood color occurs mainly in the wood rays,
and in such cases a hand lens will aid in observing it.
A 0. 1 percent solution of methyl orange in water works the same way.
Methyl orange is more easily obtained than Benzo Yellow.
The chemicals have been found to give generally good results with Oregon
white oak, white oak, chestnut oak, swamp chestnut oak, northern red
oak, black oak, scarlet oak, and roble (Quercus copeyensis), a Costa
Rican species of oak. They are apparently about equally effective on
green and on seasoned wood. Indefinite or erratic results may be ob-
tained, however, when they are applied to wood treated with preserva-
tive chemicals, to wood exposed to long weathering, or to wood infected
by stain or decay fungi, molds, or the organisms present in "sour"
logs. Consequently, the test is not recommended for use under any of
UNIVERSITY OF FLORIDA
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Test for Pine 3 1262 09216 7377
The boundary between heartwood and sapwood is frequently difficult to
recognize with certainty in the pines. A chemical solution found to'be
effective in distinguishing one from the other in southern yellow pine,
lodgepole pine, and red pine, and which gives fairly good results with
western white pine, sugar pine, and ponderosa pine as well, can be
made as follows:
Dissolve 5 grams of benzidine in 23 cubic centimeters of 25 percent hy-
drochloric acid and 970 cubic centimeters of water. (NOTE: Concen-
trated chemically pure hydrochloric acid contains about 38 percent of
the acid; to make a 25 percent solution, pour out 25 cubic centimeters
of chemically pure concentrated acid and add to it enough water to make
38 cubic centimeters of liquid. )
Next, prepare a 10 percent solution of sodium nitrite.
When ready to make tests on wood, mix the two prepared solutions in
equal amounts. When the mixture is applied to the wood, color reaction
takes place in a few moments, the sapwood appearing yellowish brown
and the heartwood red.
The mixture does not produce useful colorations on beech, oak, larch,
the spruces, Douglas-fir, or the true firs.
Test for Douglas-fir
The heartwood and sapwood of Douglas-fir can usually be differentiated
with a 0. 75 percent water solution of sodium alizarine-sulfate (Alizarine
Red S; Alizarine carmine). This indicator, which changes color in the
pH range of about 3.7 to 5. 2, stains the heartwood and one or two adja-
cent annual rings in the sapwood yellow and the sapwood pink, or some
other shade of red. The indicator works on both dry and green wood,
and the colors are comparatively permanent. The test works best on a
freshly exposed surface. A little alcohol added to the solution will make
it wet dry wood more rapidly.
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I ASIGULTUR| MADISON