The most skilled work of the craft. The bricks, known as Rubbers, are made oversize from a clay with a high sand content and free from flaws; they are bright red and consistent in colour. The soft texture of the brick allows it to be sawn and rubbed (traditionally on a York Stone) to very accurate dimensions and moulded. The finished accuracy, with sharp arises, permits the work to be constructed with very fine 3mm joints by using a neat lime mortar which gives the characteristic white joint. Gauged work is used for high quality arches over door and window openings; for circle on circle work (see Arch Construction), and for moulded work.