Bur

Bur, in an engraving, is a slight ridge of metal raised on the edges of a line by the graver or the dry point. It produces an effect like a smear, and is therefore usually regarded as a defect, and scraped off. Some etchers, however, take advantage of it to deepen their shadows, and Rembrandt made use of it in this way with telling effect. As the bur soon wears off, in valuable old proofs its presence is strong evidence of the early date of an impression.