smalti refers to the coloured vitreous paste from which tesserae for wall mosaics are obtained. It is basically ordinary glass coloured with metal oxides. The molten glass is pressed flat to form the circular discs known as pizze. These are broken up into tesserae after they have cooled. Smalti is weather resistant and easy to cut, its choice of colours is nearly unlimited and they vary according to the type of oxide used in their making.
Flat rectilinear tesserae made by pouring molten opaque colored enamel onto a steel slab, allowing it to cool, and then cutting it into small flat or cubed pieces called tesserae. The s malti are composed of silica, an alkaline substance such as soda or potash, lead, metal oxide coloring agents, and tin oxide for opacity. Opaque tesserae were desirable to avoid a shiny reflective surface when using mosaics as copies of paintings in St. Peter's Basilica. Smalti means “enamels”( smalto means enamel) in Italian, but used in English as a singular term, enamel. We say micromosaics are made of enamel, not “enamels.”.