Purfling is an inlay that runs several millimeters inside the edge of the belly and back. Purfling is generally made of three strips of wood glued together and is designed to prevent any damage to the edges from spreading into the plates. Regularity and good craftsmanship in executing the purfling are considered quality criteria. The purfling is usually made of two strips of wood dyed black glued to either side of a middle strip of light wood. This inlay is sometimes also used as a stylistic feature to distinguish between different schools of violinmaking.