larger toward the edge where sapwood joins heartwood. The appearance of gumlike substance on the surfaces and edges and its concentration in an area bordering the juncture of sapwood and heartwood closely resemble certain characteristics of brown stain.

FIGURE 3.-Upper, kiln-brown stain in sugar pine lumber. Lower, yard-brown stain in eastern white pine showing the dark-brown color developing in stock during prolonged air seasoning and storage

These drops appear on the surfaces of the sapwood portion of the board regardless of how resinous the adjoining heartwood may be. In 1915 M. B. Pratt made a study of brown stain in air-seasoned sugar pine and found no fungus associated with the discoloration,

He came to the conclusion that the stain was of chemical origin and in some way connected with an oxidation process. "The presence of the sugary sap in sugar pine probably has something to do with the oxidizing process, resulting in brown stain, which is so common in lumber of that species. It is generally found as a distinct band between the heart and sap wood.'

KILN BROWN STAIN

Kiln brown stain is one of the most troublesome and costly defects developing in kiln-dried stock of western yellow pine and sugar pine. (Fig. 4.) It has been reported as a defect in western white pine, but in this wood it is relatively unimportant. It has also been observed in incense cedar.

Kiln brown stain has been observed to some extent in the heartwood of both western yellow pine and sugar pine but is most commonly found in the sapwood, where its characteristics resemble closely those of yard brown stain. The color variations are similar, and the white margin at edges, ends, and surfaces of boards and near the juncture of heartwood and sapwood are very pronounced. The discoloration is usually more intense just behind this white strip.

MOISTURE TRANSFUSION THEORY

Whether the age and condition of the timber seem to have more influence upon the development of kiln brown stain than does the period of time during which logs are stored either in the woods or in the pond remain to be proved. Doctor Meinecke's opinions of the former view and his further observations on kiln brown stain in western yellow pine, quoted below, are of interest.

2

The entire appearance and distribution of the stain gives one the impression that the staining matter was not formed in situ but was contained in a liquid which had moved about in currents set up by the drying process and came to a standstill, accompanied by concentration, below the white outer layer and also when it reached the heartwood. The stain is due to a pronounced staining of the walls of the tracheids, including the ray tracheids. The cell walls in the clear layers, including the broken and bent fibers of the rough surface, are unstained.

CONCENTRATION OF STAIN

Apparently the concentration of color near the ends, edges, faces, and the heartwood region can be explained on the theory of moisture transfusion from the interior of the board to points near the surfaces. While the board is drying, the water solutions move toward the areas where evaporation is taking place. The greatest evaporation usually occurs at the ends, and here the color is deeper and more often observed. The white margin is often wider at this point. The heartwood, usually containing a lower moisture content than the sapwood, induces a rapid transfusion from the sapwood adjacent to it. In this case evaporation takes place somewhat the same as if the board were cut off at the juncture of heartwood and sapwood. This explanation may well fit the case in regard to the stained areas, but

2 Meinecke, E. P., letter of June 18, 1923, on results obtained on field study of brown stain in western yellow pine at Susanville, Calif.

what of the white margins bordering the darker areas? It is my belief that these white areas represent the layers of cells in which free water was present only in the early stage of drying and later contained moisture in the form of vapor or at least under conditions

FIGURE 4.-Upper, kiln-brown stain in the sapwood of incense cedar showing the characteristic white margins at end of board. Lower, kiln-brown stain in the sapwood of western yellow pine. Note the white margin at end of sample and in the sapwood adjacent to the heartwood

unfavorable to the transportation of soluble substances. The concentration of color at the edge of this white layer indicates a deposition of the coloring matter out of solution at the point where the water changed to vapor and was therefore incapable of carrying it

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farther. This would explain the hidden type of brown stain so common in both kiln-dried and air-seasoned stock.

A few simple experiments served to substantiate the transfusion and deposit theory. Small sticks of Sitka spruce 5 inches long were placed upright in test tubes containing a brown liquid collected from test tubes in which rot fungi had been grown on wood. The brown liquid formed a water-soaked area which extended up the sticks to within 2 inches of the tops. Here appeared a definite limit to the water-soaked area, which continued to become darker day by day as the water evaporated from this region and the brownish substance was left in the wood. At the end of the test dark-brown bands, darker at the upper margin, were formed near the edges of the water-soaked areas. Sticks of sugar pine 8 inches long were similarly tested, the liquid in this case being a sugar solution. In one other case the stick was shortened so that the end was an inch below the mouth of the tube. After allowing evaporation to continue for three days, the sticks were baked in an oven at 212° F. (100° C.), causing the sugar to turn slightly brown. A heavy deposit of sugar was detected at a point about 1 inch back from the exposed ends of the sticks projecting from the tubes, leaving the inch area at the tip with little or no sugar or discoloration. The other sticks showed heavy sugar deposits at the ends, this deposit extending to the tips of the sticks. The sugar solution constantly flowing to the top of the stick, where evaporation was taking place, slowly concentrated at this point.

TEST WITH BLOTTING PAPER

A similar test was conducted using 8-inch strips of white blotting paper. After two days' exposure the ends of the blotting-paper strips which projected beyond the mouths of the test tubes showed a layer of yellowish color, where the sugar solution had concentrated during evaporation. A heavy deposit of sugar was noted at the projecting ends of the paper strips.

Experimentally it was possible to cause brown stain to appear upon a particular surface. Pieces of green western white pine and western yellow pine sapwood were wrapped in heavy waxed paper with but one end of the pieces exposed. The wrapped pieces were dried in an oven at 212° F. for 48 hours. When removed all surfaces were bright, with the exception of the exposed ends, which showed a deep-brown stain behind the usual white margins. Evaporation took place almost entirely from the exposed ends, and it was here the brown color was formed during the latter part of the drying period. Other pieces were completely wrapped in the paper, having designs cut out on one side of the wrapping and then placed in the oven. Brown stain developed in the areas on the wood exposed by these stencil-like designs. These experiments were suggested by the fact that brown stain rarely develops in areas which are in close contact with crossers or stickers.

The so-called sugar in sugar pine is not a true sugar but a chemical compound called pinite or, more properly, pinitol. Collections of a white crusty exudation from the sapwood at the ends of sugar-pine logs when tested were found to have a saccharine taste. A similar

FIGURE 5.-What sap stain may do to a board.

The sap gum board to the left is clear, without sap stain, while the one to the right is heavily blue stained. Both boards have been planed. The unstained board has been steamed prior to air seasoning while the stained board has been air seasoned without preliminary steaming