The Blacksmith's Fire

Written for the beginner, this series of pages on fire detail all the skills needed to master the use of the blacksmith's coal fire and expose a few of the more commonly held myths beginners often fall prey to. Until the smith has gained total mastery over the fire, he or she can make only the simplest of objects. Add to this that all coals cannot be expected to act the same and even coal from different parts of the same seam often burn differently from each other. A thorough knowledge of how the blacksmith's fire works and how it is used helps the smith understand how to maintain and control the fire more easily and effectively.

Much more care and deliberate effort goes into building and maintaining the blacksmith's fire than most people ever realize. Correct fire tending methods absolutely must be adhered to or the fire will quickly become very inefficient or unusable. Ignoring proper cleaning and lightning techniques makes it very difficult to start the fire.

The heart of the fire burning in an average size blacksmith’s forge, is an area roughly the size of a man’s fist, and located about 2 inches above the tuyere pipe. A layer of coke and cinders surrounds the heart of the fire and they insulate and reflect heat back into the heart. This insulating layer also protects the firepot from the intense heat of the forge fire. At least an inch or more of coke must be available to cover the top of the (heart) to reflect heat back downward, for without this reflective layer, the heart would not be able to take form.

The heart of the fire is full of loose burning coke, quite the contrary to many beginner and hobbyist’s idea that the heart is hollow. The fire is kept loose throughout its area so air may freely pass through the coke. The minute the fire is allowed to burn hollow (an igloo fire sought by hobbyists) without more coke immediately replacing the consumed fuel, there will be a corresponding and substantial drop in available heat energy with which to heat the iron. This means the iron will take longer to reach a forging heat, will scale more due to increased heat time the increased oxygen level resulting from lack of fuel, and may not be able to obtain the desired heats for forging. The heart of the fire is a mass of burning coke. In a hollow fire only the inner walls of the fire are burning and it cannot heat iron much over a red heat. In a properly maintained fire the heart  is able to reach a white hot temperature with the help of an insulating layer of coke and cinders surrounding it and preheated air blast coming up through the loose mass of burning coke beneath.

Unnecessary or excessive disturbance of the fire should be avoided. The area of burning and non-burning coke that surrounds and reflects heat into the heart of the fire may be several inches or more thick. Beneath the heart and directly in the path of the blast air from the tuyere, is a layer of loose burning coke about 2 inches thick. As blast air passes up through this burning layer it is preheated before reaching the heart. The air blast must be evenly distributed to avoid developing ‘hot spots’ (small unevenly distributed hot and cold areas) in the fire. The air must be allowed to circulate freely around and through the burning coke to supply the necessary oxygen for combustion. A clogged or packed fire will impede this airflow. Coke is very fragile and easily crushed or broken into small pieces. Poor methods of inserting iron into the fire for heating, and improper or excessive use of fire tending tools will break up or pack the coke restricting or cutting off the air flow through the fire.

Coke is the desirable byproduct of the destructive distillation of coal. Coke is almost pure carbon and is grayish-black in color and much lighter than coal. Exposure to the intense heat of the blacksmith’s fire drives off the volatile matter of the coal leaving behind coke. If soft coal is left undisturbed in a mass as the fuel is coking, the volatile matter boiling out of the coal will congeal the mass together leaving behind a solid mass of coke. The latter trait is very desirable to reduce waste and to produce the larger pieces of coke the blacksmith prefers to handle. This doesn’t mean the smith only wants large pieces of coke, rather it means large pieces are easier to move and coke is easily broken into smaller pieces for final use.

Volatile matter is driven off as a thick smoke. This smoke should be encouraged to take flame and burn so to reduce the harmful effects to our environment.

Since the coke in the forge fire is constantly being consumed during fire use, more coke must be made to replenish the fire during use. This is done by raking and shoveling more coal onto and around the edges, of the fire. Water sprinkled onto the coal prior to and during the coking process sometimes helps the mass congeal better. Some smiths pour water over their coal supply in the coal tub as well. However pouring of anything but a light sprinkle of water into or near the fire should be avoided because anytime water comes in contact with a hot cast iron firepot, the firepot will crack or break. Water poured onto a hot brick fire surface will break or deteriorate the surface of the brick also.

Undesirable compounds or elements in the coal may adversely effect the iron and prevent good welds. For those reasons the coal must be coked prior to being pushed into and used in the heart of the forge fire.

As stated above, coke is in reality, a byproduct of heating coal. The fire is constantly consuming fuel and the blacksmith must continue to feed coal and coke into a fire as it is consumed. Coal is converted to coke during the process and it is the coke that produces the higher heat needed to obtain the high heats needed to bring the iron to red and yellow heats. Coal absorbs heat and should not be allowed to enter the fire, and should be allowed time to 'coke' if it does enter the fire. Always the coal is raked onto the top of the mound of burning coke so to allow the heat of the fire to convert it to coke. Coke burns much hotter and cleaner than coal and this will be clearly visible during normal fire handling when using coal as a fuel.

Using the Fire