LATTEN, denotes iron plates tinned over, of which tea-canisters are made. Plates of iron being prepared of a proper thinness, are smoothed by rusting them in an acid liquor, as common water made eager with rye : with this liquor they fill certain troughs, and then put in the plates, which they turn once or twice a day, that they may be equally rusted over ; after this they are taken out, and well scowered with sand, and, to prevent their rusting again, are immediately plunged into pure water, in which they are to be left till the instant they are to be tinned or blanched, the manner of doing which is this: they flux the tin hi a large iron crucible, which has the figure of air oblong pyramid with four faces, of which two opposite ones are less than the two others. The crucible is heated only from below, its upper part being luted with the furnace all round. The crucible is always deeper than the plates, which arc to be tinned, are long ; they always put them in downright, and the tin ought to swim over them ; to this pur pose artificers of different trades prepare plates of different shapes ; though M. Reaumur thinks them all exceptionable. But the Germans use no sort of prepara tion of the iron, to make it receive the tin, more than the keeping it always steeped in water till the time; only when the tin is melted in the crucible, they cover it with a layer of a sort of suet, which is usually two inches thick, and the plate must pass through this before it can come to the melted tin. The first use of this covering is to keep the tin from burning; for if any part should take fire, the suet would soon moisten it, and re duce it to its primitive state again. The blanchers say, this suet is a compounded matter ; it is indeed of a black colour, but M. Reaumur supposed that to be only an
artifice, to make it a secret, and that it is only coloured with soot or the smoke of a chimney ; but he found it true so far, that the common unprepared suet was not sufficient ; for after several attempts, there was always something wanting to render the success of the operation cer tain. This whole secret of blanching, therefore, was found to lie in the prepa ration of this suet; and this, at length, he discovered to consist only in the first fry ing and burning it. This simple opera tion not only gives it the colour, but puts it into a condition to give the iron a dis position to be tinned, which it does sur prisingly. The melted tin must also have a certain degree of heat, for if it is not hot enough, it will not stick to the iron ; and if it is too hot, it will cover it with too. thin a coat, and the plates will have several colours, as red, blue, and purple, and upon the whole will have a cast of yellow. To prevent this, by knowing when the fire has a proper de gree of heat, they might try with small pieces of iron ; but in general, use teach es them to know the deg-r; e, and they put in the iron when the tin is at a differ ent standard of heat, according as they would give it a thicker or a thinner coat. Sometimes also they give the plates a double layer, as they would have them very thickly covered. This by dipping them into the tin, when very hot, the first time ; and when less hot, the second. The tin which is to give the second coat must be fresh covered with suet, and that with the common suet, not the prepared.