This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
In soldering or brazing large work of copper, silver, etc, an open fire is used, called the braziers' hearth. For large and long work, this hearth is made with a flate iron plate about 4 ft. by 3, which is supported by 4 legs, and stands on the floor at a sufficient distance out from the wall, so that the operator can get all around it. In the centre of this plate is a depression about 6 in. deep and 2 ft. long by 1 wide, for containing the fuel and fire. The fire is depressed in this way so that the surface of the plate may serve for the support of large work, such as long tubes, large plates, etc. The rotary fan is commonly used for the blast. The twyer iron is similar to those for the common blacksmiths' forge, but with a larger opening for admitting the blast to the fire. The nose or top of this twyer iron is fitted loosely into grooves, so as to admit of easy renewal, as they are burned out in a very short time, and must be replaced to do good work. The fire is sometimes used the full length of the hearth, in which case a long or continuous twyer is employed. Occasionally 2 separate fires are made on the same hearth. In this case, they are separated by a loose iron plate.
The hood or mouth of the stack is suspended from the ceiling over the hearth with counterpoise weights, so that it may be raised or lowered, according to the magnitude of the work. The common blacksmiths' forge fire is frequently used for brazing. It is temporarily converted into a braziers' hearth by being built hollow around the fire, and the fire removed from the wall or flue, out into the centre of the hearth. But the brazing operation injures the fuel so that it cannot be again used for ordinary forging of iron or steel. For want of either the braziers' hearth or the blacksmiths' forge, the ordinary grate made be used, or it is better to employ a brazier or chafing dish containing charcoal, and urge the fire with a hand-bellows, which should be blown by an assistant, so that the operator may have both hands at liberty to manage the work and fuel. The best fuel for brazing is charcoal, but coke and cinders are generally used. Fresh coals are highly injurious to the work, on account of the sulphur they contain, and soft or bituminous coal cannot be used at all until it is well charred or converted into cinders.
Lead is equally as injurious in the fire for brazing as for welding iron and steel, or in forging gold, silver, or copper, for the lead is oxidized and attaches itself to the metals that are being brazed or welded, and prevents the union of the metals, and in all cases it renders the metal brittle and unserviceable. There are many kinds of work which require the application of heat having the intensity of the forge fire or the furnace, hut in a number of these cases it is only desirable to heat a small portion of the work, and avoid soiling the surface of the remainder and also to have the work under the observation and guidance of the operator, as in brazing or soldering small articles of jewellery, silver plate, etc. In these cases, the blowpipe with pointed flame is generally used, and in many cases the work is supported upon charcoal so as to concentrate the heat upon it.