P11,ASTER, (from the French, pilaslre, or Italian, piles tro,) in architecture, a square column, sometimes insulated, but more frequently let into a wall, and only projecting with a fourth or fifth part of its thickness.
The pilaster borrows the name of each order, and has the same proportions, capitals, members, and ornaments, with the columns themselves.
The pilasters in the Attic order are sometimes at equal distances, and sometimes coupled ; but this depends on the intereolumniation of the order below. If the Attic order be straight, and immediately over it, it must partake of the same distances, and stand over the column in the lower order.
Pilasters are made, usually, without either swelling or di minution, as broad at top as at bottom : though some of the modern architects, as M. Mansard, &c., diminish them at top, and make them swell in the middle, like columns; particu larly when placed behind columns.
Pilasters, M. Perrault observes, like columns, become of different kinds, according to the manner in which they arc applied to the wall. Some are wholly detached, and called by Vitruvius parasintcc ; others have three faces clear out of the wall ; others two ; and others only one : these are all called by Vitruvius ankc.
Insulated pilasters are but rarely found in the antique. The chief use they made of pilasters was at the extremities of porticos, to give the greater strength to the corners.
There are four principal things to be regarded in pilasters ; viz., their projecture out of the wall, the diminution, the dis position of the entablature, when it happens to be common to them and to a column, and their flutings and capitals.
1. The projecture of pilasters, which have only one thee out of the wall, is to be one-eighth of their breadth ; or, at most, not above one-sixth. When they receive imposts against their sides, their projecturc may be a quarter of their diameter. They are made to project in different proportions to their diameters, as one-eighth, one-fourth, one-half, and three-fourths ; but are never used gracefully quite square, except at angles ; and then only in massive buildings, as the portico at St. Paul's, Covent Garden.
2. Pilasters are hut seldom diminished, when they have only one face out of the wall. Indeed, where they stand in the same line with columns, and the entablature is continued over both, without any break, the pilasters arc to have the same diminution with the columns ; that is to say, on the thee respecting the column ; the sides being left without any dimi nution. When they are diminished, they have an ill effect ; where it becomes necessary to make them correspond with the lines of the columns at top, as is sometimes the case in porticos and returns, then it is better fur the architect to make them entirely of the smallest diameter of the column to which they are opposed.
Pilasters arc sometimes fluted, though the columns they accompany are not so ; and, on the other hand, the columns are sometimes fluted, when the pilasters that accom pany them are not. The flutings of pilasters are always odd in number, except in half pilasters, meeting at inward angles; where four flutings are made for three, 4. The proportions of the capitals of pilasters arc the same as to height with those of columns, but t hey differ in width, the leaves of the former being much wider ; because pilas tern, though of equal extent, have only the same number of leaves for their girt, viz., eight. Their usual disposition is to have two in each thee in the lower row, and in the upper row one in the middle, and two halves in the angles, in the turns whereof' they meet. Add to this, that the rim of the vase, or tambour, is not straight, as the lower part is, but a little circular, and prominent in the middle. In pilasters that support arches, the proportions, Palladio shows, must be regulated by the light they let in ; and at angles, by the w eight they are to sustain. For which reason, says Sir floury Wotton, a rustic superficies best becomes them.