A gas forge is a metalworking forge heated with gas, often propane, although other gases may be used. Gas forges provide even, consistent, and controlled heat for blacksmithing activities ranging from shoeing horses to fabricating custom tools. Numerous companies manufacture them along with accessories. It is also possible to build a custom forge, often with inexpensive materials. Directions for building forges can be found through blacksmithing organizations and do-it-yourself publications.
Forges create a hot environment for raising the temperature of metals to make them workable. The forge includes a partially closed chamber to allow heat to rise, with openings for ventilation and access. The metalworker places items into the forge, allows them to heat to the desired temperature, and removes them to work. It may be necessary to reheat a piece several times while working on it, as the metal will cool quickly in the open air, and the blacksmith must also temper the metal appropriately.
In a gas forge, gas jets are the source of heat. The operator can adjust them to reach the desired level of heat and can also control the environment with fans and bellows. Metalworkers judge the heat of their metals by appearance and their experience; the more experienced a metalworker is, the easier it is to judge whether a piece is workable yet, on the basis of prior pieces. Tools like tongs, hammers, and anvils allow the operator to handle extremely hot metal with a low risk of injury.
The size of a gas forge can vary. Farriers carry portable forges in their trucks or vans, for example, to allow them to shoe horses on site. An industrial gas forge may be much larger. The larger the forge, the more energy is required to heat it. Consequently, companies are careful to select a size appropriate for their needs. The forge must be carefully engineered to facilitate the proper flow of air through the device.
There are safety concerns around a gas forge, including the risk of burns from sparks or direct contact with heated metal. Blacksmiths typically wear heavy clothes and protective aprons made from fire-resistant materials. Some may wear goggles for eye protection, and gloves are used to protect the hands. In a communal workshop or factory floor, there may be policies about activities around the forges, such as only allowing necessary personnel into the area when the forges are lit, to reduce the risk of injuries.