The freshly cut cork planks, or " tables," as they are called, have a natural transverse curve, corresponding with the shape of the tree from which they have been peeled. In order to flatten them, they are either heaped one upon another (with the concave side downwards) in deep trenches, plentifully moistened with water, and pressed beneath huge boulders ; or, simply placed with the convex side towards a fire, and kept there till the heat has removed the warp. Previously to this operation, the variously sized " tables " will have been reduced as nearly as possible to uniform dimensions of about 3i ft. long by 1 ft. wide. The next step has for its object the closing of the pores of the cork, as non-porosity is the quality which chiefly determines the value of the article. The finest kind is compact and firm, without being hard, of even texture or grain, and slightly pink in colour. The most common method of filling up the cavities in crude cork is by placing the tables before an open fire, and heating them till the surfaces are partially charred or singed, the heating being conducted with great care, and the sides changed constantly. The objection to this process is that it causes the secretion of an empyreumatic oil, which is given off, and may be taken up by any liquid with which it cornes in contact. An attempt was made to avoid this evil by using young cork, whose texture was already so close as not to require heating ; but this was attended with little success, as the young cork was too thin for ordinary purposes, and could only be used by cementing several layers together. A much better plan, now often followed, is to boil the tables, scrape the surface, and then dry them in the sun. The pores are more effectually closed, and the sun-dried variety has none of the blackness of that dried by artificial heat. The " tables " are tied in bundles for transport to market.
Cork is not the only product of the cork oak. The inner hark of the tree contains about 12 per cent. of tannin, whose properties resemble those of catechu rather than the tannin of most other vegetable matters. It affords scarcely any of the light fawn-coloured deposit called " bloom," and it is doubted whether it is susceptible of conversion into gallic acid. It is not in favour with tanners, principally because it imparts a dark colour to leather on which it is used, and also because it yields no bloom. Its tanoin is more easily extracted than that present in English oak bark, and, when used, it is generally mixed with the latter, or with valonea. Marseilles annually imports large quantities of it ; in Italy, it is almost exclusively used in tanning sole leather ; and, years ago, Ireland imported 8000 to 10,000 tous annually. It is only produced where the.trees are most abundant, as its collection entails theirdestruction. (See Tannin.) The uses of cork among ourselves are pretty generally known ; but some of its applications where it is indigenous seem sufficiently curious. In Spain, beehives, kitchen pails, pillows, and window lights are made of it ; in Portugal, it forms the roofing of houses, linings for garden walls, and fences for poultry yards ; in Italy, images and crosses are carved out of it, footpaths are paved with it, and it is sometimes used in the buttresses of village churches ; in Turkey, it forms cabins for the cork cutters, and coffins for the dead ; ,in Morocco, it appears in the form of drinking vessels, plates, tubs, and house conduits ; and in Algeria, shoes and wearing apparel, saddles and horse shoes, armour and boats, landmarks and fortifications, furniture, stable-racks, and doorsteps, all consume their share. In England, its greatest and most important application is the manufacture
of stoppers for bottles and other vessels, which are always known as " corks." Until recently, these corks were all cut from the " tables " by hand, and, though several machines have been invented for the purpose, many are still manufactured by manual labour. The workman sits at a bench, which has a ledge round it, to prevent the corks falling off. The knife (Fig. 509), which has a very thin and sharp blade about 6 in. long, tapering, and with a trun cated end, is either placed edge uppermost in a notch en the bench, or is held in the hand. By a few dexterous circular cuts, the cork is turned out of the table, the size corresponding with the thickness of the latter. Wine-corks, &c. are cut across the grain ; bungs are cut with it. The Duchy of Olden burg, in Germany, employs probably more hands in the cork cutting industry than any other country in the world, the yearly product amounting far into millions. The work is performed at home by the whole family, after the fashion of the tenement-house cigar makers. Prices vary, but 5s. per diem is reckoned good wages ; for the family to earn this sum, they must be skilled hands, and work hard for twelve hours. The spongy nature of cork necessitates that the edge of any instrument used to cut it should he brought into contact with it by a very drawing stroke, and the edge becomes dulled so quickly that it needs rubbing on a very fine-grained stone after every few strokes.
The chief obstacles in tbe way of employing machinery for cork-cutting are the rapidity with which the edge of the cutter becomes dull, and the necessity for providing the means of adjusting the cutter so as to economize the cork, by making slight deviations from the cylindrical form where such are rendered desirable hy the shape of the crude block, in order to entail the least possible waste.
The cork-cutting machine shown in Fig. 510 requires only one attendant, who works by hand, and releases the finished cork by a tbot lever. It will cut corks or bungs either parallel or tapered, being provided with a second motion for taking off a seeond cut when required, and a stop pin for gauging the thickness of the cut and tbe diameter of the cork at once. It will make corks and bungs from in. to 4 in. diameter, and from in. to 3 in. long. T1,e chucks are thirty-one in number, varying from in. to 3i iu. diameter, the larger ones made of gun-metal, and the smaller of beet wrought iron. The manipulation of the machine is easily learnt, and from 30 to 40 gross of corks can be turned out per day of ten hours.