Principal Materials

Silica, lime and soda are the three fundamental ingredients that constitute most glass. They must be combined in precise proportions. To this, aluminium, potassium, borax, magnesium and barium oxide are added to give the glass lustre and resilience.  At this point, the mixture is in powder form and must be well mixed.

Colour is achieved by adding metallic oxides. Example: Cobalt oxide produces blue; nickel oxide produces opaque white, magnesium oxide produces amethyst; chrome oxide produces green and copper oxide produces turquoise.

Fusion

This process takes place overnight in the furnace, an oven where the temperature is maintained at about 1450°C (2250°F). By the next day, the mixture will have melted into a homogenous liquid form to become molten glass. To thicken it, the oven temperature is lowered to 1150°C (2100°F).

Shaping

The artisan works with a long hollow rod called a “BLOWPIPE”. He inserts the blowpipe into the oven and uses it to “GATHER” a ball of glass about the size of an orange. The glass is kept uniform by a constant rotation of the pipe. At this point, the artisan’s skill and experience are put to the test as the glass is blown, gradually cooled and then shaped using simple wooden or steel tools. A description of the many steps in this relatively short process would be quite lengthy.

Much can be learned by observing the glassblowing process, as can our visitors, who never seem to tire of the opportunity to see our artisans at work in the studio.

Annealing

Once the object has been shaped and cooled, a delicate operation remains to be performed: annealing. This process aims to reduce, or at best, to remove the stress in the glass caused by the shaping and cooling of the material. Annealing makes the objects more resistant to breakage caused by heat and handling. To accomplish this, the objects are placed in an oven at about 520°C (950°F). The temperature is adjusted depending on the thickness of the glass. The objects are then gradually cooled.

Source: Verrerie de Villetelle, France