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white powdery substance appears on the upper sapwood surfaces of sugar-pine boards stored on crossers in sheds for drying.

PREVENTION OF KILN BROWN STAIN

The entire problem of brown stain centers upon methods of prevention, since any bleaching or decolorizing process would appear to be too costly and cumbersome.

The majority of kiln operators interviewed believe that the kiln brown stain develops during the early part of the kiln schedule. possibly within the first two or three days. Observations made by A. Hermann, of the Western Pine Manufacturers' Association, indicate that, under certain conditions at least, the brown discoloration begins to show toward the end of the run. There appears to be a wide difference of opinion, however, as to the physical causes of the defect. Some believe it is due to an acid condition of the sap influenced by the temperatures and humidities of the kiln run. Some claim the so-called sugars in the sap are responsible for the discoloration after the heat of the kiln has caramelized this substance. Others do not attempt to determine the cause, but claim that high humidities and high temperatures are responsible, while low humidities and low temperatures are effective in preventing the defect.

At three of the mills visited, where it was claimed that the brown stain had been greatly reduced by modified schedules, it was observed that slower drying and therefore longer runs resulted. In most cases the modified schedules were not entirely successful when boards were used which had been cut from "old" logs. Kehoe 3 states that "old logs when decked in the yard are more subject to brown stain than when pond stored, and the older the logs the slower the drying schedule necessary at the start of the run, if brown stain is to be avoided or lessened." At the plant he cites a preliminary steaming is not used. At the end of the run a final conditioning of five hours at the highest relative humidity obtainable is then used to minimize casehardening. In the next 24 hours the temperature is increased from 150° to 180° and there held until a relative humidity of 8 to 10 per cent is reached throughout the kiln, at which point the stock is ready to be removed. Mr. Kehoe believes "that high temperatures and the resulting rapid transfusion at the beginning of the run when the stock is green are the causes of brown stain in all western soft pines."

Morse finds kiln brown stain more common in the top courses of edge-piled boards where the moisture content is also much lower than in the bottom courses.

He holds that dryness rather than moisture is a very important factor in producing brown stain and recommends high humidities in order to equalize the moisture content in all the boards and to prevent casehardening. Morse believes in stopping the run before the stock becomes dry enough to cause the brown color to appear.

If the boards are removed from the kiln while fairly moist, the substances dissolved in the water within the wood, though fairly concentrated at this stage of drying, may not be concentrated enough

Kehoe, A. J., Prevention of Brown Stain: Timberman 25: 62; May, 1924. KilnDrying Western Yellow Pine: Am. Lumberman, p. 68: May, 1924.

Morse, G. A., New Theory of Kiln Stain: Timberman 27: 74, 76; March, 1926.

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FIGURE 6.-A, Southern yellow pine board clear of stain. B, the same species of wood discolored by blue stain

to be altered in color by the action of heat. It appears also that as long as the majority of the heat is being used in changing the water in the wood to vapor no change in color takes place in the concen trated solution, but as soon as a certain low moisture content of the wood is approached sufficient heat is available to cause the material left in the wood to turn brownish in color.

From the facts already gathered it seems reasonable to suppose that slower drying during the early part of the run, resulting in a slower diffusion of the liquid containing the coloring matter, would prevent or reduce its concentration at the points of evaporation. A reduction of temperatures at the end of the run when the moisture content becomes low enough to allow the material in solution to concentrate would suggest itself as another angle of attack.

At some mills the practice is to cut the green stock thicker than usual and thus allow for considerable planing, which removes the outer brown-stained wood. At one mill in California, where the pine stock is given a preliminary air-seasoning of from 20 to 30 days and then kiln-dried, no brown stain develops. This observation, in connection with the fact that brown stain is less frequent in air-seasoned than in kiln-dried stock and that air-seasoned stock is subjected to slower drying at lower temperatures and humidities, appears to favor slow drying and low temperatures and humidities in kiln practices. Also, the temperatures are low at the time when concentration of the material in solution takes place. A great deal of experimental work needs to be done before a beginning may be made in the control of kiln brown stain. So long as the fundamental causes of this stain are unknown, control methods can not be expected to give uniform and satisfactory results.

BROWN SAP STAIN

The brown-colored stain due to fungous infection of sapwood was observed on pieces of western yellow pine box boards in shipments from a western State to Madison, Wis., and described as "scorch of pine lumber. The next collection came from Dr. J. S. Boyce, who sent samples of western yellow pine from Oregon showing brown sap stain and blue stain in the sapwood. It is common in jack pine (P. banksiana) and red pine (P. resinosa) of the Lake States and in western yellow pine throughout western Montana, northern and central Idaho, eastern Washington, Oregon, California, and British Columbia. It was observed in a few cases in sugar pine at California mills, and a stain closely resembling it was noted in western white pine at a large Idaho mill. One collection was made of this sap stain in pinon pine (P. monophylla) from Arizona. From the data so far gathered the causal fungus appears to develop best in species of the yellow or pitch pine group.

Field observations lead to the conclusion that this fungus enters logs held in storage for a considerable period. The stain is usually observed extending 1 to 4 feet inward from the ends of boards and from a few inches to 2 or 3 feet in the wood surrounding injuries or dead-branch knots. It has not been observed developing in lumber piled in the yard for air-seasoning.

Hubert, E. E., Some Wood Stains and Their Causes: Hardwood Record, 52: 17-19. Illus. Mar. 25, 1922.

When thin sections of the brown-colored sapwood were examined under the microscope the wood cells showed a large number of tangled brownish threads developing within them. These threads were more densely grouped in the ray cells and account for the flecking observed as one of the characteristics of brown sap stain. No evidence was found that the fungus attacked the wood cell walls. This fungus apparently obtains its food from the cell contents in a manner similar to the blue-stain organisms.

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The numerous brown stains are difficult to distinguish one from the other, and because each type presents a different problem in prevention the characteristics of each need to be learned in greater detail. The following key, therefore, may prove helpful in identifying the various brown stains found in wood:

KEY FOR THE IDENTIFICATION, BY COLOR, OF THE BROWN STAINS IN WOOD

A. Stains found in both sapwood and heartwood, caused by agencies other than fungi_.

A-1; A-2; or A-3.

A-1. Yellow to dark-brown stains in air-seasoned stock_ A-1-a.
A-2. Yellow to dark-brown stains in kiln-dried stock_ A-2-a or A-2-b.
A-3. Yellowish to blackish brown stains, mostly super-

ficial, due to machine burning or other causes-- A-3-a or A-3-b.
A-1-a. In eastern white pine, sugar pine, and western yellow

pine, caused by chemical action in wood__YARD BROWN STAIN.
A-2-a. In sugar pine, western white pine, and western yellow
pine, caused by certain combinations of temperature
and relative humidity during kiln-drying--KILN BROWN STAIN.
A-2-b. In white pine and other woods, as a result of too high
temperatures during kiln-drying, causing a scorching
or charring of the wood____

-----KILN BURN.

A-3-a. In many woods a dark-brown to blackish surface stain
due to machine burning by saw or planer----MACHINE BURN.
A-3-2. In many woods, particularly those of light color, a yellow-
ish brown to blackish-brown surface discoloration in
irregular patches and outlines due to the accumulation,
condensation, or dripping of water on surfaces__WATER STAIN.

B. Stains found in sapwood only, caused by fungi__-_-_

B-1. Chocolate-brown stain penetrating deep into sapwood of boards cut from old logs; streaked, irregular, flecked. In ends of boards or logs of western yellow pine, jack pine, red pine, and to some extent in the white pines-

STAINS PRODUCED BY FUNGI

B-1.

BROWN SAP STAIN.

The numerous stains caused by the class of fungi commonly known as molds vary in color from yellow, pink, red, purple, or brown to blue, green, and black. The molds in question are usually found on sapwood. They are characterized by cottony or downy-sometimes powdery-surface growths of various colors. Some of them cause no interior staining of the wood but by their variously colored surface growths produce blemishes which are readily planed off and in some cases can be brushed off. Other molds, such as the bluestain fungi, cause stains deeper in the wood which can not be surfaced off. (Fig. 5.)

* Hubert, E. E., The Brown Stains of Lumber: Timberman, 27: 61; August, 1926.

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The deeper stains are due to growth within the wood of minute threads of fungi. In some cases the wood structure is apparently stained by some coloring matter produced by these fungous threads. The mold fungi are very small plants which absorb their nourishment from the wood they inhabit, feeding principally upon the cell contents. As the threads grow they pass from one wood cell to another, usually through the wall of the wood fiber itself.

BLUE STAIN

Blue stain or blue sap stain is so well known that no special effort is here needed to familiarize lumbermen with this defect.

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FIGURE 7.- Showing the threads of a blue-stain fungus in shortleaf pine, decomposing the medullary ray at A, and penetrating the cell walls at C and D, mainly through natural openings. Enlarged about five hundred times

Blue stain is often found in the same piece of sapwood containing brown sap stain. This grayish-blue to bluish-black stain develops, with but few exceptions, in the sapwood of a great many woods. Occasionally a bluish stain is found in the heartwood of Sitka spruce and a very few other species where moisture conditions are favorable. The blue sap stain establishes itself in the freshly cut log, develops in stored logs, and continues to develop in the lumber cut from such logs. It also appears with unbelievable suddenness and in great amounts in lumber freshly piled. Lumber and other wood products once seasoned and again moistened may also become bluestained. A very peculiar and troublesome type of sap stain is often encountered in the seasoning of thick stock. This defect, which

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