I 
KILN DRYING HANDBOOK 45 
ant, but they are hard to apply because of the high temperatures re- 
quired to make them plastic. Paraffin has proved unusually satis- 
factory as an end coating for stock during air seasoning, but it 
can not be employed in the kiln because of its low melting point. 
Cold coatings should have about the consistency of heavy sirup. 
The amount of filler required for them ranges from one-half to 4 
parts by weight to 1 of the vehicle. They, of course, must be allowed 
to dry a few hours before being subjected to kiln temperatures. 
The two best cold coatings developed at the forest products labora- 
tory are hardened gloss oil thickened with barytes and fibrous tale, 
which is very cheap, and high-grade spar varnish and barytes, a 
more expensive mixture. 
The gloss oil coating is made as follows: The oil itself should be 
a thick grade, made up (by a paint manufacturer) of about 8 parts 
of quicklime, 100 parts of rosin, and 57.5 parts of a thinner, such as 
mineral spirits. To 100 parts of the gloss oil add 25 parts of barytes 
and 25 parts of fibrous tale. One or two parts of lampblack may 
also be added if a black coating is desired. The fibrous talc helps 
to prevent the settling out of the pigment. Any paint manufacturer 
can make up this coating. It can also be mixed by the user as needed, 
if the proper grade of gloss oil is obtained. 
A list of the most usual hot dips follows. They are effective in 
the order given. 
213° coal-tar pitch (inexpensive). 
254° eoal-tar pitch (inexpensive). 
Rosin and lampblack; 100 parts of rosin to 7 parts of lampblack (mod- 
erate in cost). 
When hot dips are used, the wood should be dipped one-half inch 
into the liquid. 
Excessive shrinkage of the wood and also rough handling often 
cause the end coating to chip or to shear off, and a fresh application 
of coating material must then be made; when this is necessary, the 
weight of the sample must be corrected accordingly. To reduce 
end drying sufficiently the coating, either original or patched, must 
cover the entire end surface and must also be sufficiently thick. 
Although coating the ends of kiln samples is imperative, such 
treatment of all the stock in the kiln is desirable only in difficult 
drying and is considered economically justified solely in unusual 
cases, such as the drying of heavy vehicle parts, gunstock blanks. 
and shoe-last blocks. 
WORKING UP OPERATING DATA 
The oven-dry weight of the kiln sample is found by multiplying 
its original weight by 100 and then dividing by 100 plus the moisture 
content expressed in per cent. Assuming that the sample originally 
weighed 3.75 pounds and that the first two moisture sections aver- 
ages 25 per cent moisture, the oven-dry weight of the sample is 
3.75 pounds < 100 _ ! 
ero on 3 pounds. If the moisture content were ex- 
pressed as a decimal instead of in the form of percentage, this 
formula would be still simpler; the oven-dry weight then is 
3.75 pounds _ 
mos 3 pounds. 
