Translation:Dictionary of French Architecture from the 11th to 16th Century/Volume 1/Abacus
ABACUS (also:"Trencher") Shelf which crowns the capital of the column. This architectural element plays a great part in constructions of the Middle Ages.
The capital receiving the springings of the arches directly, forms a corbelling intended to balance the overhang of the diagrid on the column, the abacus thus adds to the projection of the capital, giving a greater resistance; generally bevelled in the capitals of the primitive Romance time (1), it affects in flat projection, the square form according to the lower bed of the springer than it supports; it is sometimes decorated with simple mouldings and ornaments, particularly during the 12th century, on Isle-de-France, Normandy, the Champagne, Burgundy and the méridionales provinces (2). Its plan remains square during first half of the 13th century, but then it is more decorated only by profiles of a cut very-male (3), always overflowing the foliages and ornaments of the capital. The example that we give here is drawn from the chorus of the church of Vézelay, circa 1200 to 1210.
About the middle of the 13th century, when the arches are overhanging with accentuated mouldings presenting out of cut projections included/understood in polygons, the abacuses register these new forms (4). Then the foliages of the capitals overflow the projection of the abacus. (Church of Semur in Auxois and cathedral of Nevers.)
One often meets circular abacuses in the buildings of the province of Normandy, with the cathedral of Coutances, in Bayeux, in Have, the Mount-Saint-Michel; the circular abacuses appear about the middle of the 13th century: the profiles high, are deeply overhanging it, like those of the English capitals of the same time. Sometimes in the chapitaux ones of the mullions of windows (as in the Ste Chapelle of the Palate, as with the cathedral of Amiens, as in the windows of the side chapels of the cathedral of Paris), 1230 to 1250, the abacuses are circular (5).
Towards the end of the 13th century the abacuses decrease little by little by importance: they become low, thin, not very projecting during the 14th century (6), and disappear almost entirely during the 15th (7). Then, under the influence of ancient architecture, the abacuses take again importance at the beginning of the 16th century. {See:. Capial.) During the Romance period and first half of the 13th century, the abacuses do not form part of the capital; they are taken in another stone base; they fulfill really the function of a shelf being used of support and point of support with the diagrids of the arcs. Since the medium of the XIII E century until the rebirth, while losing of their importance like moulding, the abacuses, generally, are taken in the base of the capital; sometimes even the foliages which decorate the capital come to bite on the lower limbs their profiles. To the 15th century, the ornaments wrap the moulding of the abacus, which hides under this excess of vegetation. The relationship between the height of the profile of the abacus and the capital, between the projection and the contour of its mouldings and the provision of the foliages or ornaments, is extremely important to observe; because these reports/ratios and the character of these mouldings change non-seulement according to progress of the architecture of the Middle Ages, but also according to the place which the capitals occupy. To the 13th century mainly, the abacuses are more or less thick, and their profiles are more or less complicated, according to whether the capitals are placed more or less close to the ground. In the high parts of the buildings, the abacuses are very-thick, largely shaped, while in the low parts they thinner and are finely profiled.