Filigrana a reticello
and filigrana a retortoli

These two techniques, dating back to the sixteenth century, enjoyed a wide revival during the eighteenth and nineteenth centuries. They require the use of small transparent glass rods with inner threads of lattimo or coloured glass.

When the threads take on a spiral form, the technique is called filigrana a retortoli. When the threads are interwoven, then the technique is called a reticello or double filigree. To obtain the a reticello filigree, two cylinders with opposite spirals are blown and appropriately opened, and then inserted one inside the other, welding the walls together. In this way a characteristic diamond design is achieved, with a tiny bubble of air trapped at the centre of the losanges. The filigrana a retortoli technique, also known as zanfirico, involves joining the characteristic transparent canes while hot with interwoven threads incorporated into them to obtain a unique glass pattern, which is then worked and blown into the desired shape. During the 1950s, Paolo Venini and his glassmasters perfected different variations of zanfirico glass works, all showing an elegant and essential design.

Zanfirico vases, 'Paolo Venini and his Furnace'