Ghiacciato (frozen) or ghiaccio (ice), is a glass with a surface having a kind of "craquelure".
The effect is obtained by plunging the semi-finished article into water for just a few seconds when it is still hot (about 800° Celsius) and then exposing it to the heat of the furnace again.This process can be repeated several times when a more marked effect is required.
The sudden cooling of the surfce, while the innermost mass is still in the molten state, determines a powerful and non uniform contraction of the volume in a thin layer, that thus exhibits apparent breakages similar to a spider's web.
The subsequent reheating of the item eliminates any residual tensions: this prevents the extensions of these surface cracks.
This technique has been known since antiquity and was much in use in the 16th Century in the production of glasses and bowls.
It was used in the early twentieth century in the production of lighting fixtures that enhance its very special features for the distribution of light.