Corsi Collection of Decorative Stones

Class III
Gypsums (Gessi)

There are several types of gypsum, but the one which can be used for decorative purposes is called compatto. It is also known under the names of alabastrite and alabastro gessoso. It has as a base calcium sulphate, and it does not effervesce in acids. There are entirely opaque gypsums, others are translucent, and some entirely transparent. They are so soft that they can easily be marked with the fingernail, and therefore they either do not take a beautiful polish, or they soon lose it. Brongniart. 84

According to Brongniart i , 'The varieties of lamellar and compact gypsum, known under the name of gypsum alabaster, that are susceptible to taking a polish are often used as small tables or other furniture; but because of their low degree hardness they do not keep their shine for long. … It is said that the ancients used this stone instead of glass in order to let a pale and mysterious light into the temples; and it is thought that this is the stone they called phengite'.

For more information about phengite, see no. 137.

Gypsum is hydrated calcium sulphate, and the fine-grained compact variety is named 'alabaster' by geologists. It should not be confused with the alabastri in this collection, which are composed of calcium carbonate. The Italian word 'gesso' translates as both gypsum and chalk, but the latter refers to the chalk used on blackboards, which is manufactured from gypsum. The rock formation that geologists know as 'the Chalk' is a limestone.

The gypsum alabasters of Volterra and Castellina Marittima have been used for sculpture since Etruscan times in the 8th century BC, an industry that faded in medieval times but was revived in the 17th century and continues to this day. Competition in medieval times came particularly from the alabaster 'factories' of the English midlands which used local gypsum deposits to mass-produce statuary for churches and monuments.

i. Brongniart (1807) vol.1, 182


544. (135.1) Gesso della Castellina in Tuscany. Entirely of dirty snow white, and opaque. (Not common).

545. (135.2) Gesso di Volterra. Entirely white and transparent. Some people have thought that this may have been the Marmor Phengite of the ancients. It is used a great deal for vases and lamps, on account of its transparency. (Common).

See note to introduction above for Phengite.

546. (135.3) Gesso di Jesi. Mixture of white, and grey, transparent. (Not common).

547. (135.4) Gesso di Matelica. Grey ground streaked with darker grey. (Not common).

548. (135.5) Another from the same place. Light grey ground waved with white. (Not common).

549. (135.6) Another from the same place. Entirely light grey with some white lateral veins. (Not common).

550. (135.7) Another from the same place. Entirely dark grey delicately flowered with whitish. (Not common).

551. (135.8) Gesso di Volpino in the Veronese area. [p136] Entirely light grey, and almost like aventurine. (Not common).

552. (136.9) Gesso di Faenza. Mixture of white and grey. Takes a poor polish. (Common).