A picot is a loop of thread created for functional or ornamental purposes along the edge of lace, ribbon, crocheted, knitted or tatted material. These loops vary in size, according to their intended function and to their creator's artistic intention.
The word picot is pronounced [pē' kō]. It is a diminutive derived from the French verb piquer, meaning 'to prick'.
To create a picot in tatting, the first half of a double stitch is made. However, instead of pulling that half-stitch taut against the stitch before it, the half-stitch is pinched against the foundation thread and held some distance from the stitch before it. The distance at which the half-stitch is held indicates the final size of the picot. The second half of the stitch is formed, and this stitch is slid down the foundation thread and into place next to the stitch before it. The resulting picot is then anchored between two double stitches. It is also possible to anchor the picot between the two halves of a full double stitch. See Carrie Carlson's clear instructions for picot stitching.
Where picots formerly were used largely for ornament, they are now used functionally as well. In tatting, the picot is the site of the join between two rings, chains, or other pieces of work. This means that rather than creating some volume of independently-tatted rings or chains and then sewing or tying them together, an integral system of picots can be used to join these rings and chains as the work progresses.
In older tatting and crocheting patterns, picots were sometimes specified as purls, purl stitches, or pearl stitches. These specifications are not to be confused with the reverse stitch known as a purl in knitting.
Nicholls, Elgiva. Tatting: Technique and History. Dover Books, 1984 edition. ISBN 0-486-24612-4.