The gypsum rocks that the furnace used to exploit emerge in the surroundings, at same level, embedded into sandstones and clays of light colour despite its continental origin from the Upper Priabonian, in the boundaries from Eocene epoch to Oligocene, about 34 Ma ago. The southern slope of Montcogul range, as seen from Artés or from Cabrianes, bottom up displays the stratigraphic sequence of the red mudstones, the light gray layers containing the gypsum of La Carrera and, above and further east, the lake limestones that hold the plain of Roques Albes, providing substantial changes in the type of continental sedimentary rocks within the thick geological formation Artés and in the colours to the landscape.
The gypsum furnace of La Carrera is made of stone and it has a detached hut. It benefits from the slope that would’ve contributed to keep the heat. The furnace itself is fully made of sandstones, though the lower entrance and the hut have also a few gypsum stones. The furnace shape is conical; it has a wide and long entrance to load firewood at the bottom, a second upper, narrow and lateral entrance to load gypsum stones, and, on top, a small hole as a chimney.
The process of cooking gypsum should’ve started building a dome of big gypsum stones leaving an air chamber below where to place the fire and strong enough to hold the remaining gypsum stones to load through the up entrance. The oven should’ve been on fire for a few days and kept hot and covered for a few more days. Once the gypsum was fully cooked and the furnace cold, the ashes and the cooked gypsum could be removed. The furnace converts natural or dihydrated gypsum [CaSO4·2H2O] into cooked o hemihydrated gypsum [CaSO4·½H2O]. Still, this cooked gypsum from the furnace must be milled to obtain plaster powder for building and decoration purposes.
The images show the gypsum furnace of La Carrera from the outside –photo 1st; the entrance on the left corresponds to the hut, the one on the right to the furnace – and its inside –photo 2nd; see the light rays coming in through the chimney hole and the up entrance- and a natural gypsum rock from the surroundings, as the ones the furnace should’ve processed –photo 3rd.
The furnace is very old and it was restored. No oral or written documentation from its operation is preserved.