There are many ways of annealing steel: e. heating it to redness in the open or hollow fire, and then burying it in lime, in sand, in cast - iron borings, in dry sawdust, and by packing in carbon in an iron box and heating the whole to redness. This last process is the most effectual, provided the steel is not heated to excess. A layer of coarsely powdered wood charcoal is placed at the bottom of the box, then a layer of the steel, and so on until the box is nearly full, finishing with charcoal. The lid is luted with clay or loam; the whole is then placed in a furnace or hollow fire, and gradually heated to redness. Overheating is hurtful. It is seldom necessary to keep up the heat beyond the time when the contents of the box are uniformly heated, unless the steel should contain particles of hard impure iron, when it would be necessary to keep up the heat for several hours. When the whole has arrived at the proper temperature, the box is withdrawn from the fire and buried in hot or cold ashes to become quite cool, or left in the fire, and the fire allowed to cool down.. The steel should be protected from air until it becomes cool, when it is taken out of the box, and is ready for the fitting or turning room.

It is then very soft, and free from those hard bright spots which workmen call "pins." The surface of the steel will be as free from oxidation as before it was heated, and the greater portion of the charcoal will remain unconsumed, and can be used again. This mode of annealing prevents the steel from losing its quality; but it absorbs a small quantity of caroon, which is favourable to the hardening process. Animal charcoal is sometimes used.

If time will not admit of a piece of steel being softened in a box with charcoal powder, it may be heated to cherry - redness in an open fire, then drawn out of the fire, and allowed to cool till the redness is not visible by daylight, but can be seen in a dark place, then plunged at this heat into cold water, and allowed to remain in the water until it becomes quite cool. When taken out of the water, it will be more uniform in temper than when it left the forge. This is a very expeditious way of annealing; but the steel will not be quite so soft as if it were enclosed in the iron box in contact with charcoal powder. Steel required to be annealed in such large quantities as to make it inconvenient, or the expense of enclosing it in Loxes too great, may be heated in a charcoal fire completely enveloped and protected from the air. After the steel is heated to the proper temperature, the fire and the steel may be covered with pieces of plate iron, the whole then covered with cinder ashes, and the fire allowed to go out of its own accord. It will thus be protected until it is cold. Charcoal, especially when used as fuel in the open fire, is consumed with rapidity, and therefore very expensive.

A cinder fire is less expensive; it is not so pure as charcoal, but purer than coal, and affords a very moderate heat. When the steel is at the proper heat it is taken out of the cinder fire and placed in an iron box containing coarsely powdered charcoal, which must completely envelop the steel; the box is covered up and luted with clay or loam, in order to exclude the air and preserve the charcoal for future use.

Cast - iron may be annealed in a similar manner. In the state it leaves the moulds it is always surrounded with a crust or coating, sometimes so hard that the best file will make no impression upon it, while the interior of the casting is soft and manageable. This hard crust js generally removed either by chipping with the cold chisel, or by grinding on a large grinding - stone turned by machinery. But when the shape of the casting is such that this crust cannot conveniently be so removed, annealing is the most economical process, as it makes the whole casting soft and much easier to work, but does not deprive it of its natural character. The heat requires to be kept up much longer than for steel, and the iron needs solid supports to keep it from bending or breaking by the heat. When annealed, it is more uniform in temper, consequently less liable to alter its figure by subsequent partial exposure to moderate heat. The outside is always somewhat harder than the inside, unless such processes be adopted as will extract the carbon from the former; but these processes deprive it of its natural character and make it in the condition of mallable iron, but without the fibre which is due to the hammering and rolling.

Cast - iron cutlery is enclosed in boxes, and cemented with some substance containing oxygen, such as poor iron ores free from sulphur, scales from the smith's anvil, and various other absorbents of carbon. The boxes are luted as when annealing steel or case - hardening iron; they are afterwards placed in suitable furnaces, and the cast articles are kept in a state little short of fusion for 2 or 3 days, when they are found to possess considerable malleability, and can be readily bent and slightly forged, (Ede's Management of Steel,)