With growing demand for processed iron, there grew a corresponding demand for charcoal, which could produce a temperature many times higher than unprocessed wood, much needed for the forging of steel weapons. The forges were supplied by charcoal-burners, who spent most of the year living in the forest by their charcoal kilns – great piles of stacked wood covered in clay with just a few vents for air, where, in an oxygen-starved atmosphere the wood slowly pyrolyzed to charcoal. Each pile would smoulder and give off much smoke for several weeks, during which time it had to be delved through repeatedly. After it burned out completely, the yield of the process – charcoal – was unearthed from beneath the clay. The charcoal was then sold at a special market bearing that name, quite separate from traders in other goods. During the reign of Wenceslas IV, the charcoal-burners already had numerous rights and freedoms regarding use of the forests, and were held in relatively high esteem.
Resin was sold exclusively by wagoners and resin merchants, who themselves made pitch for greasing their wheels. The charcoal burners produced resin and pitch only as a side-line. The pitch merchants provided pitch to tanneries to impregnate leather and mixed it with tallow to grease the axles of wheels on wagons and carriages.