Selection and Preparation of Animal Glue for Use 
Making strong joints depends primarily upon having the proper 
correlation of gluing pressure and glue consistency at the moment pressure 
is applied. With animal glue solutions, the consistency depends on the 
cooling and drying effects. For the first few minutes after an animal glue 
has been spread on the wood the cooling effect is much more important than 
the drying and this temperature-viscosity relationship varies with the grade 
and with the concentration of the glue solution. High-grade animal glues 
thicken to the proper pressing consistency quicker and at higher tempera- 
tures than do low-grade glues of equal concentration. Assuming glues of 
equal grade, one mixed with less water will thicken more rapidly than one 
mixed with a greater quantity of water. 
Warm animal glues, as they normally exist in the spreader, are 
too thin for pressing and some thickening must occur "before pressure is 
applied. The best consistency for pressing exists when the glue is thick 
enough to form short, thick strings when touched with the finger but not 
thick enough to resist an imprint or a depression readily. The thickening 
time or assembly period is usually fixed by the operating conditions that 
dictate how much time shall elapse between spreading and pressing. The 
grade of glue and the proportion of water added in mixing become, therefore, 
the variables by which the manufacturer can fit the glue mixture to his 
operating conditions. When once established, the grade and proportion of 
water should be adhered to except as temperature changes in the gluing room 
or wood require a change in the mixture. 
The following tabulation shows the grades, with the corresponding 
ratings for jelly strength and viscosity, as established by federal specifi- 
cations for animal glue for woodworking ( 1 3 ) ; 
Grade 
VI 
V2 
Jl 
J2 
SI 
S2 
As a general rule, the following division of grades is recommended 
for different uses and service conditions: 
VI and V2 for general use in veneering where assembly periods may 
be somewhat prolonged. 
Jelly strength 
Viscosity 
(grams ) 
(millipoises) 
150-194 
57-68 
195-239 
69-81 
240-284 
82-95 
285-329 
96-1C9 
33C-37U 
110-124 
375-419 
125-139 
R492 -6- 
