Though simple enough as regards the mere process, in practice line engraving demands a peculiar dexterity. When the outlines of the drawing that is to be copied have been traced and transferred to a plate usually made of copper,[1] the metal is attacked with a sharp tool, called the dry-point. Then the trenches thus marked out are deepened, or fresh ones are made with the graver, which, owing to its shape, produces an angular incision. The appearance of every object represented in the original must be reproduced solely by these incised lines: at different distances apart, or tending in various directions: or by dots and cross-hatchings. Line engraving possesses no other resources. Moreover, in addition to the difficulties resulting from the use of a refractory tool, we must mention the unavoidable slowness of the work, and the frequent impossibility of correcting faults without having recourse to such drastic remedies as obtaining a fresh surface by re-levelling the plate where the mistakes have been made. Etching by means of aquafortis, originally used by armourers in their damascene work, is said to have been first applied to the execution of plates in Germany towards the close of the fifteenth century. Since then it has attracted a great many draughtsmen and painters, as it requires only a short apprenticeship, and is the quickest kind of engraving. Line engravers have not only frequently used etching in beginning their plates, but have often employed it, not merely to sketch in their subject, but actually in conjunction with the burin. Many important works owe their existence to the mixture of the two processes, among others the fine portraits of Jean Morin, and the admirable "Batailles d'Alexandre," engraved by Gérard Audran, after Lebrun. But at present we are only occupied with etching as practised separately and within the limits of its own resources. The artist who makes use of this method has to scoop no laborious furrows. He draws with the needle, on a copper plate covered with a coating of varnish, suggestions of form as free as the strokes of pen or pencil. At first these strokes only affect the surface of the copper where the needle has freed the plate from varnish. But they become of the necessary depth as soon as a certain quantity of corrosive fluid has been poured on to the plate, which is surrounded by a sort of wax rampart. For a length of time proportioned to the effect intended, the acid is allowed to bite the exposed parts of the metal, and when the plate is cleaned proofs can be struck off from it.