It's such a simple word, but generates all sorts of heated discussion when it comes to blacksmithing. There is a lot of folklore and hearsay about it, and maybe this can sort some of it out for the reader.

It all starts as vegetation. About 100 years worth of vegetation will form one foot of peat. It takes about 4 feet of peat and another 400 years to make one foot of coal. Further aging time, heat and pressure result in the various grades of coal that we have today. These grades are generally classed as follows (from lowest grade to highest grade):

Peat, Lignite, Sub-bituminous, Bituminous, Semi-bituminous, Semi-anthracite, and Anthracite.

Peat, Lignite, and Sub-bituminous are extremely high in moisture, but a bit low in fixed carbon, and burn relatively cool. Semi-anthracite and Anthracite are low in moisture, have plenty of fixed carbon, and burn plenty hot, but lack the necessary volatility and coking properties needed. That leaves us with Bituminous coal for the forge.

Yes, we all basically know this, but Bituminous coal varies widely in quality and gradings. The following table represents a good range of typical analysis results for forge coal:

• Carbon (high) 55-65%
• Moisture (low) 2.5-3.0%
• Ash (low) 3-8%
• Sulfur 1-2%
• Volatility (high) 30-40%
• BTU (high) 13,500-14,500
• Coking Button (free swell index) 6

  note: It has been my experience that the lower the volatility, the lower the Coking Button. This can be very important to those who wish to do a lot of welding at the forge.

Your coal dealer should be able to provide you with the typical analysis of the grades of Bituminous with which they deal. Compare it to what you found here and make your decision accordingly.

Written by Dave B. This e-mail address is being protected from spam bots, you need JavaScript enabled to view it