A slip consists of extremely fine grained clay particles which are sorted out from the clay matrix by soaking in water. Typically a slip is a clay suspended in water. It is often applied to exterior and interior vessel surfaces of unfired pottery as a method for strengthening the bonds between coils, to create a smooth surface or to hide a dark or rough body. Most commonly slips are used to give a pot a finer surface, or a different colour to that of the main body of the ceramic. The use of slips dates to the first development of ceramics. In China slip coating is especially common during the Song Dynasty. Vessels can also be decorated by having designs painted with slip in low relief, in same or a contrasting color as the ground, or by having designs incised or excised (carved ) in or through the slip.