Tatting is a technique for handcrafting a particularly durable lace constructed by a series of knots and loops. Tatting can be used to make lace edging as well as doilies, collars, and other decorative pieces. The lace is formed by a pattern of rings and chains formed from a series of cow hitch, or half-hitch knots, called double stitches (ds), over a core thread. Gaps can be left between the stitches to form picots, which are used for practical construction as well as decorative effect.