CORK 



439 



bark, and increase its volume and elasticity, to remove the tannic acid, 

 and straighten out the curvature of the individual pieces for convenience 

 in packing. The boiling is done by placing the pieces close together, one 

 on top of another, and compressing by a heavy weight to keep them flat- 

 tened out. Boiling softens the outer bark so that it may be scraped to 

 remove the coarse and hard outer layer called " hardback." This layer 

 may vary from xs to | in., depending upon the nature and character of 

 the bark. It is done by hand with hand rasps in most cases, and reduces 

 the weight of the bark about 20 per cent. Efforts have been made to do 

 the scraping by machinery, but it is generally agreed that the hand work 



Photograph bv Nelson C. Brown. 



Fig. 117. — At a large cork factory in Seville, Spain. Under the open sheds on the right the 

 crude cork is boiled and scraped. The best cork is made into wine stoppers. 



is better, because the worker can better judge the character and require- 

 ments of the individual piece and rasp accordingly. Some pieces of 

 bark are exceedingly rough and irregular and require much more scrap- 

 ing and individual attention than others. Some parts of one piece of 

 bark may also be much more irregular than other parts. 



After scraping the bark, it is trimmed with a knife either by hand or 

 by machine, and sorted into grades. It is sorted first for thickness and 

 then for quality. There are customarily from four to five grades of 

 thickness and there are usually four sub-grades of quality to each thick- 



