Raised images, etc., are produced by stamping the copper. The art of engraving these steel dies is named " die-sinking." Raised designs in copper are also produced by punches or similar tools. This is named " repousse work." Raised images can also be produced on sheet copper by drawing the design with a varnish that will resist the action of acid, and then etching the exposed parts in a bath of dilute nitric acid. A similar result may be obtained by electrical action in a bath of dilute sulphuric acid, the plate to be etched being attached to the positive pole of a battery, and a plain sheet of copper to the negative pole. The process may be reversed, if desired, by carefully scraping the design on a varnished plate and depositing copper on the exposed parts in a bath for electrotyping.