Modern Alabaster
When the term "alabaster" is used
without any qualification it invariably means, at the present
day, a finely granular variety of gypsum. This
mineral, or alabaster proper, occurs in England in the
Keuper marls of the Midlands, especially at Chellaston in
Derbyshire, at Fauld in Staffordshire and near Newark in
Nottinghamshire. At all these localities it has been extensively
worked. It is also found, though in subordinate quantity, at
Watchet in Somerset, near Penarth in Glamorganshire, and
elsewhere. In Cumbria it occurs largely in the New Red rocks, but at a lower geological horizon.
The alabaster of Nottinghamshire and Derbyshire is found in
thick nodular beds or "floors," in spheroidal masses known
as "balls" or "bowls." and in smaller lenticular masses
termed "cakes." At Chellaston, where the alabaster is known
as "Patrick," it has been worked into ornaments under the name
of "Derbyshire spar" -- a term more properly applied to fluorspar.
The finer kinds of alabaster are largely employed as an ornamental stone, especially for ecclesiastical decoration, and for the rails of staircases and halls. Its softness enables it to be readily carved into elaborate forms, but its solubility in water renders it inapplicable to outdoor work. The purest alabaster is a snow-white material of fine tiniforni grain, but it is often associated with oxide of iron, which produces brown clouding and veining in the stone. The coarser varieties of alabaster are converted by calcination into plaster of Paris, whence they are sometimes known as "plaster stone."
On the continent of Europe the centre of the alabaster trade is Florence, Italy. The Tuscan alabaster occurs in nodular masses,
embedded in limestone, interstratified with marls of Miocene and Pliocene age. The mineral is largely worked, by means of underground galleries, in the district of Volterra. Several varieties are recognized -- veined, spotted, clouded, agatiform, etc. The finest kind, obtained principally from Castellina, is sent to Florence for figure-sculpture, whilst the common kinds are carved locally, at a very cheap rate, into vases, clock-cases and various ornamental objects, in which a large trade is carried on, especially in Florence, Pisa and Leghorn.
In order to diminish the translucency of the alabaster and to produce an opacity suggestive of true marble, the statues are immersed in a bath of water and gradually heated nearly to the boiling-point -- an operation requiring great care, for if the temperature be not carefully regulated, the stone acquires a dead-white chalky appearance. The effect of heating appears to be a partial dehydration of the gypsum. If properly treated, it very closely resembles true marble, and is known as marmo di Castellina. It should be noted that sulphate of lime (gypsum) was used also by the ancients, and was employed, for instance, in Assyrian sculpture, so that some of the ancient alabaster is identical with the modern stone.
Alabaster may be stained by digesting it, after heing heated, in various pigmentary solutions; and in this way a good imitation of coral has been produced (alabaster coral).
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