Rembrandt excelled in the technique of etching. Like engraving, etching is an intaglio printmaking method, meaning that the image is incised below the surface of the plate (as opposed to relief prints, such as woodcuts). Etched lines are not cut with a burin, but are bitten with acid. The copper plate is covered with an acid-resistant ground, usually of wax or resin, and the artist draws the image into the ground with a stylus. Acid is then applied, which eats into the exposed areas. The longer the plate is exposed to acid, the deeper the bite and therefore the stronger the line. Different depths are achieved by covering some lines with acid-impervious varnish and biting others for a longer period of time. The ground is then removed and the plate inked for printing.