For large scale mosaics, workshops, such as those at the Vatican Mosaic Studio, originally used cubic tesserae, known as smalti, made from ground glass and baked in an oven like enamel. By the 1760s this art had been so perfected that it was possible to produce rods or threads of colored glass, called smalti filati, thin enough to be cut into the minute tesserae used on the present lot. These tiny individual tesserae, in an almost limitless palette of as many as 28,000 colors, allowed truly painterly compositions. The painstaking detail required to work micromosaics meant the smallest were set into snuffboxes and jewelry while larger tables or plaques were massive undertakings. By the 19th century, the Vatican workshop was producing such superior mosaic-work that it operated at the near exclusion of any other mosaic studio. Important and ancient Roman destinations such as the San Gregorio Magno al Celio monastery were favored by mosaicists during the 19th century. In the latter half of the 19th century, there were as many as ninety-six mosaicisti operating in Rome largely producing souvenirs of the Grand Tour in the form of tabletops, painterly plaques, miniatures and cameos.