14 BULLETIN 150 0, U. S. DEPARTMENT OF AGRICULTURE 
soda, which is next added. 14 Materials that are needed to give the 
glue an adequate working life or other special properties are put in 
last, and the mixture is stirred until a smooth glue is obtained. 
Stirring for 15 to 30 minutes usually suffices. A number of formulas 
for wet-mix glues have been developed at the Forest Products Labo- 
ratory some of which, with special directions, are included in the 
appendix. 
The working life of mixed casein glues may vary from less than 
an hour to several days, according to the formula used. Most casein 
glues become noticeably thicker on standing at room temperatures, 
and the quality of joints made with such glues appears to be 
unaffected so long as they can be spread satisfactorily on the wood. 
Casein glues that remain liquid for a day frequently become thinner, 
which generally indicates a deterioration of the mixture. Glues that 
have thinned appreciably should therefore be used with caution. 
Glue mixtures that will remain liquid, even though used just after 
mixing, do not produce joints of the highest water resistance. 
PREPARING BLOOD-ALBUMIN GLUES 
Blood-albumin glues are prepared by combining the individual 
raw materials at the time of mixing. Dried soluble albumin is 
generally used in the preparation of blood glues. The proportion 
of water and other materials added varies greatly according to the 
formula used and the consistency desired for the work at hand. 
Blood glues are generally prepared by traditional and undivulged 
processes. Two blood glue formulas developed at the Forest Prod- 
ucts Laboratory, with detailed directions for mixing, are given in 
the appendix. 
In mixing blood-albumin glues cold water should be added to 
the albumin. The albumin should be allowed to soak an hour or 
more before the other ingredients are added. Even after this period 
of soaking a certain amount of insoluble material will remain, and, 
if excessive, should be strained out. Other ingredients are then 
added according to formula, and the whole is stirred until a uniform 
glue is produced. 
The working life of blood glues varies considerably with the 
amount of ammonia, lime, caustic soda, or other ingredients added 
to the dried albumin. Glues can easily be mixed which have a 
working life of from several hours to several days. As with other 
glues made from animal material, precaution should be taken to 
prevent decomposition. 
PREPARATION OF WOOD FOR GLUING 
DRYING AND CONDITIONING 
The moisture content of wood 15 for gluing should be such that 
when increased by the moisture from the glue it will be as near as 
practicable to the average moisture content of the finished article. 
Moisture changes in glued wood induce stresses which favor warping 
14 Even soaking for a few minutes is helpful, but one-half to one hour is better. Soak- 
ing periods of several hours are used to advantage by some manufacturers. 
16 Instructions for determining the moisture content of wood are given in U. S. Dept. 
Agr. Bui. 1136, entitled " Kiln-Drying Handbook," by Rolf Thelen (JO), and in other 
publications of the Forest Products laboratory. 
