COOPER (Dutch kuiper), an artificer who makes casks and coops, tubs, barrels, and all kinds of wooden vessels which are bound together with hoops.
The art of the cooper is of great antiquity, and soon attained all the perfection which it at present possesses.
There are some countries, however, in which it is as yet unknown; and in others, from the scarcity of wood and other causes, earthen vessels and skins lined with pitch are used for containing liquors. The Latin word dolium, usually translated a cask, was employed by the Romans to denote earthen vessels used for the same purposes. The word dolare, to chip with an axe, to hew, from which dolium is derived, and the word dolarius, a cooper, may naturally enough be applied, the former to the construction of casks, which are made of several pieces of wood planed and fitted for joining together, and the latter to the artificer himself.
Pliny ascribes the invention of casks to the people who lived at the foot of the Alps. In his time they lined them with pitch. From A.D. 70, in the time of Tiberius and Vespasian, the art of constructing vessels of different pieces of wood seems to have been well known. Indeed, previous to this period, Varro and Columella, in detailing the precepts of rural economy, speak distinctly of vessels formed of different pieces, and bound together with circles of wood, or hoops. The fabrication of casks, on account of the great abundance of wood, was probably very early introduced into France. It is uncertain when this art was first practised in Britain; but it seems not improbable that it was derived from the French.
The figure of a cask is that of two truncated cones, or rather conoids, joined together; for the lines are not straight, as in the cone, but are curved from the vertex to the base. The part of greatest circumference is called the belly of the cask. In the choice of wood, old, thick, and straight trees are preferred, from which thin planks are hewn, and then formed into staves. In France the wood is prepared in winter: the staves and bottoms are then formed, and they are
put together, or, in the language of the artificer, the cask is mounted, in summer. Planing the staves is one of the most difficult, and at the same time most important parts of the work. In dressing staves with the plane, the workman is directed to cut across the wood, in order probably to prevent the instrument following the course of the fibres, which may not always be in the same plane with the surface of the stave, and thus render it of unequal thickness.
In the formation of the staves, it ought to be recollected that each must constitute part of a double conoid. It must therefore be broader at the middle, and gradually become narrower, but not in straight lines, towards the extremities. The outside of the staves across the wood must be wrought into the segment of a circle, and it must be thickest near the middle, growing gradually thinner towards the ends. Great experience is requisite for the nice adjustment of the different curves to the size and shape of the cask; but less attention is paid to the rounding or dressing of the inside of the stave.
After the staves have been dressed and are ready to be arranged in a circular form, it might be supposed necessary, for the purpose of making the seams tight, to trim the thin edges in such a manner that the contiguous staves may be brought into firm contact throughout the whole joint, or sloped similar to the arch-stones of a bridge. But this is not the practice usually followed by the artificer. Without attempting to slope them so that the whole surface of the edge may touch in every point, he brings the contiguous staves into contact only at the inner surface; and in this way, by driving the hoops hard, he can make a closer joint than could be done by sloping them from the outer to the inner side. In this, perhaps, and in giving the proper curvature to the staves, consist the principal part of the cooper's art. Machinery is now frequently employed in preparing the staves.