COOPER, an artificer who makes casks, coops tubs and barrels, and all kinds of wooden vessels which are bound together with hoops. It would appear, that the art of the cooper is of great antiquity, and soon attained all the perfection which it at present possesses.
But although this art is very ancient, there are some countries in which it is yet unknown; and in other countries from the scarcity of wood, or from some other causes, earthen vessels and skins lined with pitch are used for containing liquors. The Latin word dolium, is usually translated "cask;" but it was employed by the Romans to denote earthen vessels used for the same purposes. The word dolare, to "plane, or smooth," from which dolium is derived, and the word dolarius, "a cooper," may be naturally enough applied, the former to the construction of casks, which are made of several pieces of the same tree 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 the year 70 of the Christian era 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 description which they have given accords exactly with the construction of casks. The fabrication of casks, on account of the great abundance of wood, was probably very early introduced into France. When this art was first practised in Britain is unknown; 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. As the place where the junction seems to take place is the most capacious, it is commonly called the belly of the cask. In the choice of wood, old, thick, and straight trees are preferred, from which thin planks are hewn which are to be 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 parts of the work; and it is at the same time one of the most important in the fabrication of casks. In dressing staves with the plane, the workman is directed to cut across the wood; the reason of which is 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 is to constitute part of a double conoid. It must therefore be broader at the middle, and must 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 mid-
dle, growing gradually thinner towards the ends. Great experience, it is obvious, must be requisite for the nice adjustment of the different curves to the size and shape of the cask. Less attention, as it is less necessary, is paid to the rounding or dressing of the inside of the stave.
After the staves are dressed and 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 which is 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, with giving the proper curvature to the staves, consists the principal part of the cooper's art.