Fire-setting

Fire-setting is a method of traditional mining used most commonly from prehistoric times up to the Middle Ages. Fires were set against a rock face to heat the stone, which was then doused with liquid, causing the stone to fracture by thermal shock. Some experiments have suggested that the water (or any other liquid) did not have a noticeable effect on the rock, but rather helped the miners' progress by quickly cooling down the area after the fire. This technique was best performed in opencast mines where the smoke and fumes could dissipate safely. The technique was very dangerous in underground workings without adequate ventilation. The method became largely redundant with the growth in use of explosives.

Although fire-setting was frequently used before modern times, it has been used sporadically since then. In some regions of the world, notably Africa and Eurasia, fire-setting continued to be in use until the 19th and 20th centuries. It was used where rock was too hard to drill holes with steel borers for blasting or whenever it was economic because of cheapness of wood.

The oldest traces of this method in Europe were found in southern France (département of Hérault) and date back to Copper Age. Numerous finds exist from Bronze Age, such as in the Alps, in the former mining district of Schwaz-Brixlegg in Tyrol, or in the Goleen area in Cork, to name a few.

As for antique written sources, fire-setting is first described by Diodorus Siculus in his Bibliotheca historica written about 60 BC, about methods of mining used in ancient Egyptian gold mines. It is also mentioned in greater detail by Pliny the Elder in his Naturalis Historia, published in the first century AD. In Book XXXIII, he describes mining methods for gold, and the pursuit of the gold-bearing veins underground using tunnels and stopes. He mentions the use of vinegar to quench the hot rock, but water would have been just as effective, as vinegar was expensive at the time for regular use in a mine. The reference to vinegar may come from a description by Livy of Hannibal's crossing of the Alps, when it was said that the soldiers used vinegar in fire-setting to remove large rocks in the path of his army. The effectiveness of strong acetic acid solutions on heated limestone has been demonstrated in laboratory experiments.

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