The white threads in this glass are made of lattimo, or ‘milk glass’. Its opaque white colour comes from the addition of tin oxide or arsenic to molten glass, which creates microcrystals that reflect light. Here the milk-glass filaments have been fused with the transparent glass. In Italian this technique is called vetro a fili (‘glass with threads’). In the English-speaking world it is known as ‘filigree’ glass.