A very important use of copper, from the Middle Ages down to our own day, has been for engraving plates, both for etchings and the printing of maps. This art even antedated the invention of printing by movable types. The great artist Albrecht Dürer, who was perhaps the finest etcher of all time, worked very largely on copper plates; as did Rembrandt and countless others who have followed these illustrious examples. Other materials have been tried, but none has ever seriously challenged the pre-eminence of copper for this purpose. Steel engravings, for instance, were very popular in mid-Victorian days and gave very fine results; but a steel plate will rust if not stored carefully and is also harder to engrave. The copper used for engraving is alloyed with a very small addition of silver or arsenic to raise its annealing temperature slightly when heated.
Copper plates for the production of pictures and other illustrations date from at least A.D. 1430 in Germany, where they were employed to produce playing cards. 'The Passion of Christ' was engraved on a small copper plate in 1440 and, before this date, the engraved letters on the leather and parchment covers of manuscript books were made by letters in relief in brass stamps.
Copper plates were also adopted centuries ago as the best means of engraving maps. The first maps known to have been printed from copper plates were two Italian editions of the geographer Ptolemy, in 1472. Metal supplanted wood for this purpose because of the clarity and much finer detail that could be reproduced on the polished copper surface. There still exists an engraved copper globe of about 1493 which was made just after Columbus's first voyage to America.
Both in H.M. Ordnance Survey maps and in Admiralty charts the use of copper plates for map printing is traditional. These maps and charts require constant correction whenever new roads are cut or new soundings show different depths of water. Such corrections are easily made on a copper plate. The official practice has been to scrape or gouge out the old details, and then to carefully hammer back the portion of the plate in order to make the surface perfectly level once more, before inscribing the new features on it. Many of the Admiralty plates have been subjected to this procedure repeatedly for more than a century and still remain in use.