Quoins are the corner stones of buildings. They play an important part in binding the walls well together at the angles, and are often made conspicuous by better or more pretentious workmanship.

In heavy masonry they frequently project an inch or two from the face of the wall (see Figs. 122, 123), and the margin is either "sunk drafted,"l moulded, or chamfered, the face being boldly worked, "rusticated" (see Fig. 122), or left with the rough "rock" or "quarry face."

The quoins of rubble walls are often in ashlar, of a better stone, with close joints - the face being either left rough or worked according to taste.2

In some descriptions of work the quoins are made of the exact height of the courses of rubble, being first set as gauges, to which the latter are levelled: but frequently the quoins are quite independent of the rubble, and irregular in every way - no two stones are of the same size or shape, and the joints abutting against the rubble are left rough and not kept vertical (see Figs. 132, 143). Stone quoins to brick walls should be the exact depth of a certain number of courses, so that they may readily bond in to the brickwork.

1 Sunk draft is a margin, as described at page 40, sunk below the general surface of the stone.

2 The different methods of working the faces of stones, and the operations of stone cutting, do not fall within this Course.

Second Quoins, such as those shown at ss in Kg. 146, are sometimes used, where the ordinary quoins are small, in order to give additional strength to the angle of the wall. The stretchers may be doubled as well as the headers.

Window Sills (see page 10) should be worked smooth, rubbed, and weathered,1 so as to get rid of the water as quickly as possible, and throated,2 to prevent it from falling on the wall below them.

An ordinary window sill is shown in elevation in Figs. 94 and 547, and also in Fig. 15 and others. The corbels yy, shown below the sill in the latter case, may be required for support of very projecting sills, but are often added only for ornament. The most usual form of section is given in Fig. 543.

A groove should be cut along the centre of the upper surface of the sill, to correspond with one in the bed of the oak sill of the window frame, into which a metal water bar or tongue (wb, Fig. 545) is inserted, to prevent wet from getting in through the joint.

With the same view of preventing the entrance of wet, the stone sill is sometimes checked out to receive the oak sill, as shown in Fig. 540, but this is an expensive construction seldom adopted.

Different methods of finishing the ends of sills are shown in Figs. 94, 541, 542, 544, 545, etc.