Walk into any traditional forge and you'll quickly learn that coal is not just coal. The fuel you choose dictates how your fire behaves, how much control you have over temperature, and even the quality of the metal you take to the anvil. For a blacksmith, understanding the differences between bituminous coal, anthracite, and coke is as important as knowing your hammer technique.

Bituminous coal: the traditional blacksmith's fuel

Bituminous is the soft coal most associated with traditional blacksmithing. It contains a high proportion of volatile matter, so it lights relatively easily and produces a smoky, flaming fire as those volatiles burn off. As the coal heats, it swells and softens, caking together into a porous mass — the coke — which then burns with intense heat. This coking action lets you build a deep, hollow fire with a reducing zone just above the tuyere. You can bank wet green coal around the edges to be coked as needed. It does create clinker and smoke, so good ventilation is essential. For general forging and forge welding, bituminous coal offers excellent flexibility.

Anthracite: hard, hot, and demanding

Anthracite is a hard, high-carbon coal with very low volatile content. It is difficult to light and needs a steady, strong air blast to keep burning. Once going, it produces a fierce, clean heat with little smoke or flame. However, it does not coke or swell, so the fire tends to be shallower and less forgiving. You cannot easily shape the fire by banking green coal. Anthracite is excellent for sustained high temperatures and produces less clinker than bituminous, but it demands careful air control — too little air and it dies, too much and you burn steel. It suits bottom-blast forges with a constant blast. Finished work tends to be cleaner due to low sulphur, but the learning curve is steep.

Coke: the clean, consistent alternative

Coke is bituminous coal that has already had its volatiles driven off in a coking process. It looks like grey, porous, lightweight rock. It lights more easily than anthracite but less easily than raw bituminous coal. Once lit, coke burns with a steady, clean flame and very little smoke. It produces consistent heat and is easy to control — adjust the fire with the air blast and by adding fuel around the edges. Coke does produce clinker, though less than bituminous. It is favoured by blacksmiths who want a clean, predictable fire without the smoke and flare of green coal. Coke can be more expensive and harder to source in some areas. It is excellent for general forging, heat treating, and welding.

How fuel choice shapes fire control

Each fuel gives a different level of control. Bituminous coal offers the most flexible fire. You can build a large, deep fire for welding or a smaller, concentrated fire for detail work. The coking process creates a reducing zone that protects metal from oxidation. Anthracite gives intense, focused heat but a narrower margin for error. The fire is shallow, so you must manage the blast carefully to avoid burning thin sections. Coke sits in the middle: it lights predictably, burns steadily, and responds well to air adjustments. It produces a fire that is easy to maintain at a consistent temperature, ideal for repetitive work. In all cases, match the fire to the task — deep for welding, narrow for bending, clean for finishing.

How fuel choice affects finished work

The fuel you burn influences the surface of your finished pieces. Bituminous coal can introduce sulphur and other impurities, which may cause pitting or affect a forge weld if not managed. Smoke and soot can also deposit on the metal. Anthracite, being low in volatiles and sulphur, produces a cleaner heat, but its intense nature can lead to scaling if steel overheats. Coke gives the cleanest burn of the three, with minimal smoke and contaminants. This makes it a favourite for pattern welding and for work where a clean surface matters. However, coke can still produce clinker; if not removed it will interfere with the fire and contaminate the work. Whichever fuel you use, regular cleaning of the fire pot and careful fire management will reward you with better results at the anvil.

Practical tips for choosing and using your coal

Start with what is available locally. Bituminous coal is common in many parts of the UK, often sold as smithy coal or forge coal. Anthracite is available as small nuts or beans. Coke can be bought as foundry coke or breeze. When using bituminous, keep a bucket of water handy to wet the green coal and control the fire. Build a cave of green coal around the fire and rake it in as needed. With anthracite, start with a bed of burning coke or wood to get it going, then maintain a steady blast. With coke, light it with a torch or kindling and add fuel gradually. Always remove clinker before it builds up — it will block the air and ruin your fire. Experiment with different fuels to find what suits your forge, your work, and your style. The best fuel is the one you learn to read and control.