§ 103 Niello Work
Niello, which may be described as a design traced and painted on silver, as one paints and traces delicately with the pen, was discovered by the goldsmiths as far back as the time of the ancients, there having been seen in their gold and silver plates incisions made by tools and filled up with some mixture.281 In niello the design is traced with the stylus on silver which has a smooth surface, and is engraved with the burin, a square tool cut on the slant like a spur from one of its angles to the other; for sloping thus towards one of the corners makes it very sharp and cutting on the two edges, and its point glides over the metal and graves extremely finely.282 With this tool is executed all graving on metal, whether the lines are to be filled or are to be left open, according to the pleasure of the artificer. When therefore they have finished their graving with the burin, they take silver and lead and fuse them into one substance over the fire; and this when completely amalgamated is black in colour, very friable, and extremely fusible.283
The next process is to pound this substance and put it over the engraved silver plaque which must be thoroughly clean, then to bring it near to a fire of green wood, blowing with the bellows that the rays of the fire may strike upon the niello, which by virtue of the heat melts and flows filling up all incisions that the graver has made. Afterwards when the silver has cooled, the worker proceeds to remove carefully the overplus with scrapers, and with pumice stone to grind it away little by little, rubbing it with the hands and with a leather till it is reduced to the true flat and the whole is left polished. The Florentine Maso Finiguerra worked most admirably in this craft in which he was really extraordinary, as is testified to by some paxes284 of niello in San Giovanni of Florence that are esteemed wonderful.