TECHNICAL NOTE number 253 
 
 UNITED STATES DEPARTMENT OF AGRICULTURE FOREST SERVICE 
 
 FOREST PRODUCTS LABORATORY 
 MADISON 5, WISCONSIN REV4S*© Jttne~h9«n 
 
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 COLOR TESTS FOR DIFFERENTIATING HEARTWOOD 
 
 2 
 
 AND SAPWOOD OF CERTAIN OA KS , J^NESr AjNDQ R^ 
 DOUGLAS-FIR 
 
 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, 
 —J 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. 
 ?; si lytethyl orange is more easily obtained than Benzo Yellow. 
 
 q 3 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 
 these conditions. 
 
UNIVERSITY OF FLORIDA 
 
 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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