The basic organization of glassblowing in a furnace is called piazza. Nowadays the personnel of a piazza are composed of a glass-master, a servente, a serventin and a boy. In the past there was another position between that of glass-master and servente, called maestro fuori piazza, that has disappeared. He learnt the difficult glassblowing craft as apprentice. The first important glassblowing operation is weighing raw materials. Making a mistake can impair completely the consistency of glass.
After weighing the raw ingredients, they are put into a mixer. Then, the mixture is put into some crucibles. In each crucible there is an amalgam of different colour, that is obtained adding colouring substances to the glass mixture. Nowadays glassblowing involves furnaces which contain a crucible with a maximum capacity of about 1000 kilograms. The crucible is on an upper level, called banco. It divides the fusion chamber from the fire and it has a hole, called occhio, for the passage of the flames in the crucible.
In the walls of the furnace there are some openings, called bocche, provided with some devices that remain closed during the fusion. In front of each bocca there is a stone slab, called asio, that functions as support. Glassmakers are protected from heat by a refractory stone covered with a wooden board, that is provided with some prominent hooks for the support of blowpipes. Furnaces used to fuse glass mixture are fuelled by methane, that has replaced furnace oil for a long time. The substance fuses at 1400°C and this operation lasts nine hours. At 17 the glass mixture is put into a crucible at 1250°C. The load having finished, the temperature of the furnace increases to 1400°C in order to “fine out” glass and eliminate gas bubbles which come out from the liquid. This operation finishes at 2. Then the temperature is reduced to 1000°C so that glass isn’t too much liquid to be “gathered”.
At 7 glass has the proper consistency to be worked. After obtaining a mass of glass, the serventin takes a lump of incandescent material with a pipe, he presses and rolls it on an iron leaf (it was made of marble a long time ago), called bronzin, in order to make it solid and homogeneous.