32,^ 
Dept. Bull. 1500, U. S. Dept. of Agriculture 
Plate 9 
Photomicrographs of Glued Joints 
A.— Blood-glue joint between basswood veneers. Plies are at right angles to each other. Glue 
has penetrated some distance into the wood through the pores or large cell openings. 
B and C— Basswood plywood glued with animal glue under different gluing conditions. In B 
a slightly chilled glue and moderate pressure produced a strong joint. In C a thin glue and high 
pressure produced a typical starved joint. 
D and E.— Birch plywood glued with blood glue at 50 and 200 pounds pressure per square inch, 
respectively. In spite of differences in penetration and glue-line thickness, the joints gave prac- 
tically the same strength when tested. 
F and G.— Blood glue between white pine veneer. In F only sufficient pressure was used to 
keep the veneers in contact. The wide glue lines contained numerous air pockets. In G 200 
pounds pressure per square inch was used. Note thin glue line and variation in penetration 
between spring wood and summer wood. 
H.— Douglas fir blocks glued with casein glue. Very little penetration, a thin glue line, and 
weak joints between summer wood portions as compared with spring wood. Dark areas along glue 
lines in spring wood were produced by staining from the glue. 
I and J.— Cross and longitudinal sections of a starved joint in hard maple glued with animal 
glue. Note the hollow cylinders of glue in a part of the wood cells, caused by the glue tendrils 
shrinking. 
