A quoin is a column of cornerstones from the foundation to the roof. Structural quoins are weight-bearing structures laid with the brick or stone. Decorative quoins are usually made of thin finished stone cut in a 90-degree angle and attached to the outside of the corner. Quoins usually contrast with the brick or stone of the building and are placed in alternating patterns of squares and rectangles.
Mortise and tenon joints are used to connect two pieces of wood or stone to create a 90 degree angle. The basic design consists of a structural component, such as a timber or a stone slab, with a rectangular-shaped slot called the mortise. The other component has one end shaped to fit inside the slot, and is called the tenon. Wood beams may be glued or nailed together for added stability.
A pilaster is a column used in architecture to buttress walls and corners. Pilasters on the corners of buildings are called "cantons." Pilasters are a common feature of Greek Revival architecture in homes and commercial buildings in the United States. The pilaster is constructed flat on the side attached to the structure with a flat or rounded front. Pilasters are often built into the corners of brick or stone buildings to provide extra structural support.
Round corners present an aesthetic reminiscent of art deco design. Round corners depart from the traditional right angle, or 90 degree, predominant in most traditional architecture. Buildings with round corners present a sleek, modern appearance. Round corner designs utilize all available space both inside and outside the building. Some architects have designed round window corners reinforced with a steel frame.