There are several terms associated with the treatment of edges. The most basic is a cut edge; this is literally what it means. A large sheet of glass is either "cut" using a scribe and break technique or cored for circular pieces. The edges are left as is which can leave sharp edges. The next edge type is swiped or seamed edges which means that all the sharp edges are removed. The final type is a ground edge which provides an even mounting surface and gives a uniform cosmetic appearance to the perimeter of the optic. The better the treatment of the edge, the less likely it may become chipped in handling. Edge chips are not permitted within the optics' stated clear aperture. Edge chips are typically defined for optical windows and first surface mirrors to have maximum values of 0.25 to 0.5mm.