MICRO MOSAICS:

At the Vatican, c1600, a school developed the technique of making very fine glass strips called  "tesserae" and by pulling these into long strips where able to produce a huge range of hues in many colours. This technique gave the Roman school a much greater scope for creating a scenic mosaic scene than the Pietro Dura school based in Florence. With the rise of European tourism in the late 19th century, it became very fashionable the bring home an example of Roman  micro-mosaic work as a souvenir of a visit to Italy.