Hi -
to better understand the topic:
Technology
For the black mass, Cellini prescribes 1 ounce of silver, 2 ounces of copper and 3 ounces of lead, the older Theophilus 4/7 silver, 2/7 copper, 1/7 lead. The amount of sulfur is not specified. According to Pliny, the Egyptians should have made this mass of silver and sulfur in equal parts and 1/3 copper.
These constituents are to be repeatedly melted together until the black matter which breaks down into spheres on cooling shows a uniform structure. Then it is crushed and the metal to be polished, which has been moistened with water with a little borax, is completely covered with it. About glowing coals now the Niello is melted, but scraped away after cooling, so that only the recessed areas of the plate remain satisfied. Finally, the whole thing is sanded and polished. As a result, the black filled areas contrast with the shiny metal surfaces. Galvanoplastic Niello is produced in such a way that the metal objects are coated with etching base, engraved in the latter drawings and deepened by etching. The object is then placed in the electroforming apparatus until the depressed copper has filled in the features, washes the ground and grinds and polishes the surface.
Today the powder is ready to be bought in the specialized trade. Another possibility of the process: The powder is mixed with ammonia or alcohol to a fine pulp (water would start to boil when heated and the mixture from the recess hurl). This is introduced with a spatula in the wells, with a soft flame, the metal is heated, finally brought to a more pointed with the Niello. With a sharp needle, the small lead beads can be warped on the surface. If the workpiece is cold, the Niello can be filed flat, it must be noted that due to the lead content, the file may not be mixed with metallfiling, also separate tools should be used.
History
The Niellotechnik was already known in ancient Egypt and ancient Greece. The Niello was particularly popular in the Middle Ages, outstanding examples are the Tassilokelch and Paderborn Tragaltar of Roger von Helmarshausen. An outstanding master of the early Renaissance was Finiguerra in Florence around 1450.
Around 1885-1889, the Niello work had its headquarters in Russia. Most well-known were the silver tobacco cans made in Tula, but excellent works were also made in Vologda and Ustyug Veliki. A special application finds the Niello for black filling of the numerals and graduations of the minute circle on metal clock dials as well as for enameling gold watch cases.
Some classic examples - to show a few






Some catalogue pages from Soviettime with the cheap, "instant" niello


Regards
Goldstein