Alum has been used in many ways since ancient times. As a wood and flame retardant, as an additive for dyeing and tanning, and even for medical purposes. In Egypt, fragments of construction wood have been excavated which were treated with alum as early as 450 BC. The Romans dyed their togas with madder root (Rubinia tinctorum) and alum. Since the Middle Ages, alum has been used to make goat and sheepskin leather durable and supple. Alum was used externally for skin diseases, internally for intestinal diseases, as well as a haemostatic agent, the so-called shaving stick.
Alum is a salt of sulphuric acid, a so-called double sulphate, because it is a mixture of two sulphates. All double sulphates of monovalent and trivalent metals are called alum, but the most common is potassium aluminium alum, or potassium alum for short.
Alum is not found in nature in its pure form. It has been extracted from alum stone (alunite) since ancient times. It is found near active volcanoes or in desert areas, in humid climate it is washed out. In ancient times natural deposits were exploited at active volcanoes such as Vesuvius, Lipari, Stromboli, Volcano and Sicily. In the Middle Ages it mostly came from Arab countries. When 1462 Giovanno di Castro discovered rich deposits in Tolfa near Civitavecchia, the first alum plant in Europe was established there. As the mine belonged to the Papal States, Pope Pius II tried to establish a monopoly together with the House of Medici. The Easter bull of 1463 threatened to ban all those who imported or bought unchristian alum.
Shortly after 1500, alum extraction from black shale (alum shale) was discovered. Black shale is much more common and numerous new alum works were established in Europe. This led to the collapse of the papal monopoly in 1510.
Alum production collapsed shortly after 1800 as the newly emerging chemical industry replaced alum with cheaply produced sulphuric acid. Either the alum was replaced by sulphuric acid, or alum was produced from sulphuric acid in factories. Thus, black shale mining ended and mines were closed down and are now destroyed.
However, due to the chemical activity of alum shale, stalactites and stalagmites of diadochite formed very quickly in the mines. Thus several rediscovered mines were used as show mines because of the speleothems.