Alum is an aluminum and potassium sulphate, which was used in the 16th century as a mordant in fabric dyeing. The product also had other industrial, domestic and even medicinal uses. Data on alum production exists after the 15th century, when Enrique the IV granted the privilege of mining to the Vélez and Villena marquisates. The alum industry in Mazarrón went on growing until 1592, when the mines were closed as a result of declines in exportation to European countries. Starting in 1774, the mines’ activity was centered on alum waste and sediment (named “almagras”) treatment, which were used in that period for treating in the processing of tobacco. Remains of this activity in Mazarrón have been traditional in nature and operated on a small scale until recently. This production of what locals referred to as “alum,” more generally knowned as alum stone, a white coloured product used in barber shops as an “after shave” disinfectant. The old factory still maintains some parts of its facilities, such as some of the tanks, washing, and decantation basins, stone drying areas, a waterwheel base and ovens (for cooking the material). This is the oldest factory in Mazarrón, although there are two, more recent factories also dedicated to alum production.

The red coloration of sediment is characteristic of these facilities (red ocher, referred to also as almazarrón in certain places) surrounding the facilities and giving them a particular look with this unique color, which has become emblematic and identifying for Mazarrón.