Post 275 –by Gautam Shah
Alabaster has been used for decorative objects since 3500BC. It is believed that one of the sources for Alabaster was Alabastron, a town in Egypt. The Greek mineral name alabastrites is derived from that town. The word alabaster relates to Greek –alabastros or alabastos, and old French –alabastre. Alabaster also connects to ancient Egyptian word a-labaste that refers to vessels of the Egyptian Goddess Bast.
When cut in thin sheets, Calcite alabaster is translucent enough to be used for small windows. It was used for glazing (when glass was rare) in Byzantine and later in Italian medieval churches. Large sheets of Aragonese gypsum alabaster are used extensively in the contemporary Cathedral of Our Lady of the Angels, Los Angeles, in 2002. It requires special cooling to prevent the panes from overheating and turning opaque. There are several examples of alabaster windows in ordinary village churches and monasteries in northern Spain. Translucent alabaster is used for craft items like lamps and chandeliers.
‘Calcite, like most carbonates, will dissolve with most forms of acid. Calcite can be either dissolved by groundwater or precipitated by groundwater, depending on several factors including the water temperature, pH, and dissolved ion concentrations. Although calcite is fairly insoluble in cold water, acidity can cause dissolution of calcite and release of carbon dioxide gas. Ambient carbon dioxide, due to its acidity, has a slight solubilizing effect on calcite. Calcite exhibits an unusual characteristic called retrograde solubility in which it becomes less soluble in water as the temperature increases. When conditions are right for precipitation, calcite forms mineral coatings that cement the existing rock grains together or it can fill fractures. When conditions are right for dissolution, the removal of calcite can dramatically increase the porosity and permeability of the rock, and if it continues for a long period of time may result in the formation of caves. On a landscape scale, continued dissolution of calcium carbonate-rich rocks can lead to the expansion and eventual collapse of cave systems, resulting in various forms of karst topography’. (from Wikipedia).
Alabaster is translucent whitish kind of gypsum. It is a soft and easy to work or carve material used for making vases, ornaments, bottles, jars, busts and ornamental objects. A three-foot vase with a relief from Warka, of 3500-3000 BC (in British Museum), busts from Sumer, of 3000 BC (Louvre), ornate triple lotus oil lamps found in the Tomb of Tutankhamen 1356 BC, and Sarcophagus of Seti I 1304 BC, are some ancient items made of alabaster. Decorative artefacts of Alabaster have been found in Sumer, Babylonia, Assyria and Roman empire. In later periods it was used in India from 6th to 13th C.
Alabaster are broadly two classes of minerals, a sulphate of lime or a pure variety of gypsum, and the other is a carbonate of lime, akin to a marble in composition. Due to the close resemblance of the two materials, in terms colour and grain, some ambiguity in distinct identification has persisted. The gypsum alabaster or the oriental alabaster is more softer, delicate and needs care in polishing. It soon tarnishes on atmospheric exposure, and affected by dust and smoke. The carbonate alabaster is little more firmer and so more suitable for larger items. This was sourced from caves where lime water drips to form natural deposits or moulded forms. It is also called onyx-marble or alabaster-onyx, or simply as onyx. There are several types of alabaster found, including pink, white, and black.
Alabaster have been modified by various treatments. To make it opaque like a marble, its translucency is reduced by immersing the completed work in a bath of water, and gradually heating, so that stone does not become dead white or chalky. The treated material is called marmo-di-Castellina. Alabaster is also tinted to accentuate the natural veins or to add colour that matches the stone or wood in the surroundings. This is done to produce make-believe coral for decorative elements like rails of staircases, handles and trims.
Alabaster was used as translucent panels before the advent of glass, in openings of monasteries in Mediterranean countries, like Greece, France, Italy and Spain. Alabaster cut into thin sheets is translucent enough for dull interior illumination.
Inspired by dull glow of Alabaster panels, Thin Marble panels have been used as exterior wall units for Beinecke Rare Book & Manuscript Library Yale University in New Haven, Connecticut. Large alabaster sheets have been used extensively in a Contemporary Cathedral of Our Lady of the Angels, 2002 AD, The cathedral incorporates special cooling system to prevent the panes from overheating and turning opaque.