Madretinte translates to "mother tint" in English.  Madretinte is a form of smalti but super saturated with the dye oxides used to color the glass.  Used primarily in creating filati.  For example, using the Buccaro Blue, you can add varying amounts of white to obtain different shades of blue filati.

The shape of the pieces is similar to Ravenna or "B" cut smalti.