The especial branch of goldsmithing which he practised was what the Italians still call 'niello' work, or the enamelling of designs upon precious metals. The method of doing such work is this. Upon the piece to be enamelled the design is first carefully drawn with a fine point, precisely as in silver chiselling, and corrected till quite perfect in all respects. This design is then cut into the metal with very sharp tools, evenly, but not to a great depth. When completely cut, the enamelling substance, which is generally sulphate of silver, is placed upon the design in just sufficient quantities, and the whole piece of work is then put into a furnace and heated to such a point that the enamel melts and fills all the cuttings of the design, while the metal itself remains uninjured. This is an easier matter than might be supposed, because gold and silver, though soft under the chisel, will not melt except at a very high temperature. When the enamel has cooled, the whole surface is rubbed down to a perfect level, and the design appears with sharp outlines in the polished metal. Now anyone who has ever worked with a steel point on bright metal knows how very hard it is to judge of the correctness of the drawing by merely looking at it, because the light is reflected in all directions into one's eyes, not only from untouched parts of the plate, but from the freshly cut lines. The best way of testing the work is to blacken it with some kind of colour that is free from acid, such as a mixture of lampblack and oil, to rub the surface clean so as to leave the ink only in the engraved lines, and then take an impression of the drawing upon damp paper. That is practically what Finiguerra did, and in so doing he discovered the art of engraving. Probably goldsmiths had done the same before him, as they have always done since, but none of them had thought of drawing upon metal merely for the sake of the impression it would make, and without any intention of using the metal afterwards. Within fifty years of Finiguerra's invention very beautiful engravings were sold all over Italy, and many famous painters engraved their own works--foremost among these, Mantegna and Botticelli. Early Italian art rose thus by regular steps, from the helpless, traditional, imitative work of the Romanesque and Byzantine artists to its highest development. It then passed a succession of climaxes in the masterpieces of Lionardo da Vinci, Michelangelo, Raphael and Titian, and thence descended gradually to the miserably low level of the eighteenth century.