You may have heard the term alabaster used to describe the pristine skin of a beautiful woman or the smooth surface of statue, as in the case of The Mourners: Tomb Sculptures from the Court of Burgundy, on view at the Legion of Honor through December 31.
But alabaster is actually a common name that applies to a few different types of rocks. Translucent and waxy in appearance, alabaster rocks generally include calcium in their composition. The real name for the stone used to carve the Mourners is gypsum.
Gypsum is made up of the mineral calcium sulfate, which is classified as a chemical sedimentary rock. This type of rock was formed millions of years ago from the depths of a shallow sea as it evaporated. If the gypsum used to carve the Mourners were completely pure, the figures would be totally transparent.
But as a result of impurities in the mineral, the stone takes on the beautiful, creamy color that has come to be known as alabaster. However, some areas of the figures are more pure than others, and if you look carefully you’ll notice that some of the books that the figures hold are almost transparent.
Gypsum is so soft that a fingernail could easily scratch it. Geologists developed a hardness scale with 1 signifying the softest rock; gypsum has hardness of 1.5–2, which means that anything harder than this will scratch it. We therefore had to be careful not to wear jewelry, belt buckles or anything that might damage the soft surface of these objects as we were unpacking the figures and putting them on display.
The rock from which the Mourners are made was probably imported from northern Italy, where there is a good source of carving-quality gypsum still in use today. When the figures were carved during the Middle Ages, however, England and Spain also exported gypsum. To date, there have been no analytical studies to determine the actual source of the alabaster used to carve the Mourners.
Don't miss your opportunity to examine this fascinating substance and the beautiful figures it was used to carve. The Mourners: Tomb Sculptures from the Court of Burgundy is currently on view at the Legion of Honor.