March 25. 1922 



HARDWOOD RECORD 



19 



wood for structural purposes where the failure of the piece is likely 

 to cause loss of life and property. For this reason blued wood, wood 

 stained by L. pesizula (grayish olive mold) and yellow stained wood 

 should be rejected in airplane construction unless careful tests indi- 

 cate otherwise. 



Several cases have been noted where blued wood steamed and 

 bent for use in the manufacture of furni- 

 ture, barrel staves and other products has 

 failed under the bending process. It would 

 be of value to determine whether the blue- 

 stain fungus in the broken bent material 

 is the cause of the failure or whether it is 

 due to wood-destroying fungi accompany- 

 ing the blue-stain. 



In the case of steam bent and other 

 products manufactured from the sapwood 

 of red gum a wood-destroying fungus 

 (Polyporus adustus) very frequently ac- 

 companies the blue stain and no doubt plays 

 an important part in weakening the wood. 



Fungi Can Revive After Long Periods of 

 Brying 



In some of the samples studied the 

 fungi in the wood had been dormant, 



that is, kept in the dry air of a room, for a considerable length 

 of time, and in one case the blue-stain fungus had remained 

 dormant for a period of seven years in the sap zone of a piece of 

 structural timber. The blue-stain hyphae, dormant in the wood for 

 a considerable period of time, are capable of reviving and sending 

 forth new hyphae on tlu' return of favorable growth conditions. 

 This fact has an important bearing on the piling of lumber for air 

 seasoning or for storage. Boards cut from the sapwood of slightly 

 blued logs should be stored and piled in such a manner as to imme- 

 diately check by rapid drying the further development of the fungus, 

 otherwise the blue-stain will spread. It is equally important to 

 keep the material dry once it has been properly seasoned, for the 

 fungus will revive and continue to spread as long as sufficient 

 moisture is present for its growth. The loss by degrading due to 

 the development of blue-stain in stacks 

 containing sapwood lumber has never been 

 estimated. Investigative work aiming at 

 the development of the best methods of 

 piling lumber to prevent blue-stain and 

 other stains which degrade lumber is 

 greatly needed and would aid in prevent- 

 ing much of this unnecessary loss. The 

 Forest Products Laboratory is engaged in 

 a study covering these points, and ac- 

 counts of the scope of this project are to 

 be found in several of the lumber trade 

 journals. 



Methods of Control 



Fig. 3. Showing the blue-stain fungus in shortieaf 

 pine decomposing the medullary ray at A, and pene^ 

 trating the cell walls at C and D. Enlarged 

 500 times 



about 



I 



The methods of control here presented 

 do not apply to the red stain of boxelder 

 which develops in the standing living tree. 

 They are suggested for use against such 

 fungi as attack the wood after the tree is 

 felled. 



There are three possible methods of combating wood stains, as 

 follows: Air seasoning, kiln drying and treatment with antiseptic 

 solutions. 



Air seasoning, if effective, is believed by many to be the cheapest 

 method to use. Eapid handling from the time the tree is cut until 

 the lumber is properly stacked in the yards will greatly aid in 

 reducing if not preventing blue-stain and other stains which appear 

 in the stacked material. Quick drying by means of a system of 

 piling which affords ample ventilation and requires the use of 

 treated stickers will prevent the fungi from securing a foothold. 



Fig, 4. Young threads or hyphje of the blue-stain 

 fungus in the wood cells of scrub pine, showing direct 

 penetration of the cell walls. Note the constrictions 

 where the threads pass through the walls. In the 

 lower center one thread is passing through a bordered 

 pit. Enlarged about SOO times 



The best methods of handling lumber to prevent stains are in the 

 process of development, and a study along these lines is under way. 

 Kiln drying appears to be an effective method of control, 

 although definite data on the effect of the various standard kiln 

 runs on the fungi in the wood and on the development of blue-stain 

 and other stains on stock after piling are not yet secured. 



Some interesting data are here pre- 

 sented for the first time as a result of pre- 

 liminary tests made by the writer to de- 

 termine the effect of temperature on the 

 vitality of the blue-stain fungus and decay- 

 producing fungi in wood. The application 

 of such data to kiln drying is evident, par- 

 ticularly in respect to the minimum amount 

 of heat and time required for the prelim- 

 inary steaming at the beginning of the 

 run in order to be reasonably certain that 

 all fungi present in the wood are killed by 

 this treatment. 



As a result of this test it has been de- 

 termined that a temperature of 140 de- 

 grees F. maintained for three hours at sat- 

 urated atmosphere (relative humidity 100 

 per cent) kills the blue-stain fungus in 

 1-inch and 2-inch stock containing blued 

 sapwood. The fungus in the 4-inch stock remained alive in the cen- 

 tral portion of the test pieces. In six hours under the above condi- 

 tions no revival of the fungus was observed in the 1-inch, 2-inch or 

 4-ineh test pieces and similarly for the !), 12 and 24-hour tests. Three 

 species of wood, paper birch, northern white cedar and eastern 

 white pine were used in the tests which are being continued. 



Ordinary kiln drying should therefore be effective in killing 

 the blue-stain fungus and thus preventing the appearance of blue- 

 stain, providing the stock is kept in a dry, sanitary condition dur- 

 ing storage. In general it is believed that steaming the stock at 

 170 or 180 degrees Fahr. for a period not exceeding an hour will 

 stop the growth of mold. This treatment heats the surface of the 

 stock sufficiently to kill the mold, and at the same time too rapid 

 drying is prevented by the saturated air. (See Forest Products 

 Technical Note No. 136.) Tests in prog- 

 ress may show that a lower temperature 

 may be used to advantage. 



The antiseptic treatment of wood with 

 solutions to prevent staining has been prac- 

 ticed for some time with varying degrees 

 of success. Sodium carbonate, sodium bi- 

 carbonate and sodium fluoride are the 

 chemicals more commonly used in this 

 method of control, which consists of dip- 

 ping the stock as it comes from the saw 

 in a heated chemical solution. In this proc- 

 ess it is again important that the stock 

 when piled should be well ventilated and 

 the stickers or crossing strips used in pil- 

 ing should be narrow and should also be 

 treated with the chemical. This insures a 

 drier condition in the boards and prevents 

 the development of stains at the point of 

 contact with the stickers. Molds are often 

 found to be troublesome under this treat- 

 ment, as the chemicals mentioned fail to prevent mold growth. 

 Where moisture penetrates the stacks of treated lumber the so- 

 dium bicarbonate not only fails to eliminate stain, but causes de- 

 terioration in the appearance of the lumber by imparting to it a 

 3'ellowish discoloration. 



It is evident that the conditions under which the stock is stored 

 after treatment are highly important factors in the control of 

 stain. Proper methods of piling and protection of stored material 

 against moisture are vital points to be considered in preventing 

 stain. 



