Shaping metal is an art that has been around since ancient times. Metallurgy has undergone a vast evolution since fire was first put to iron, but the classic image of the blacksmith hammering tools and weaponry has remained in our culture. In medieval times, smithing was a lifetime trade, and blacksmiths built coal fired forges that were capable of producing a wide range of metal items. Whether for medieval reenactment or personal satisfaction, it is possible to create a medieval-style forge with access to the correct resources.
Construct the hearth, or the furnace where the metal will be heated. This is the most important element of any forge or smithy, and the specifications of your hearth will depend on its intended purpose. Medieval forges were made of firebricks, bricks made of heat-resistant clay called fireclay. Fireclay and firebricks can be purchased commercially, as can fireclay mortar. Set a layer of bricks where the base of the hearth will be first - remember that if the forge is intended for smithing swords, the hearth will need to be elongated. Using mortar to adhere each layer of bricks to the layer above it, carefully construct the hearth. A typical hearth has several components, including a chamber for the coal (called the firepot) with a downwards vent beneath it that leads to the front of the hearth (the tuyere, used with the bellows). The metal to be heated is placed in a chamber above the firepot that is open to the front and often contains a small chimney or vent in top for smoke.
Install the remaining equipment, such as the anvil and the slack tub. Medieval anvils were not shaped in the "London" style that is now ubiquitous in our culture. Medieval anvils were rather of a block shape, often shaped with a square or pentagonal footprint. The size of anvil required also depends upon the desired purpose of the forge; armorers especially require large anvils to facilitate the hammering of metal plates. Many medieval anvils also included specialized protrusions for creating specific items, such as horseshoes or nails. Select an appropriate anvil style and install it at waist-height several feet from the hearth. The bellows should also be kept next to the hearth. The slack tub is simply a tub of water used to quench the hot metal; in medieval times these were typically simple barrels placed next to the anvil. Blacksmithing tools such as a hammer, tongs, chisels, fullers, and hardys should also be kept handy or hung from a nearby wall.
Make the forge operational by filling the firepot of the hearth with coal and filling the slack tub with water or brine. To create the furnace heat required for the hearth, set the coal alight and use the bellows to pump air into the tuyere (the small vent in the front of the hearth which leads to the underside of the firepot). This action pushes air through the burning coals, introducing large amounts of oxygen to the fire, which in turn increases in temperature. To make tools or weapons in the forge, place an iron "blank" (an unshaped bar of appropriate size for the item being made) into the chamber above the firepot and stoke the fire with the bellows until the iron is red hot. Carefully remove the iron with tongs and use the hammer and anvil to shape it into the correct shape. Chisels or a hardy can be used to cut the metal, and fullers can be used to create grooves, rounded corners, hollows, and other similar features. The iron should be reheated as necessary while shaping, and when the product is complete it should be placed into the slack tub to quench the metal.
Be sure to build your forge in a well-ventilated area away from inflammable materials; an outdoors area with a shelter roof is typical.
Always take safety precautions when handling fire, burning materials, or red-hot metals. Wear appropriate safety gear and take care not to drop red hot metal anywhere other than the slack tub. Also be cautious when quenching metals, as the process often creates a large amount of steam.