An overview of the working techniques used in making glass art would surely begien with the Roman period, even though the first techniques and their development originate in the Eastern area of the Mediterranean, where the oldest finds in glass known today were found.
The composition of the mixture was simpler and less refined in that the materials used were primarily those that were easy to obtain. The first elements were glazes or fused products such as silicates, alkalis and carbonates, with secondary elements being material that added colour and glass fragments.
The former were obtained with sand and broken down minerals, such as sandstone and quarzite for the silicates, and the ashes and burnt plants or mineral soda made up the alkalis: sea shells found in the sand provided the necessary calcium to make the glass less soluble in water. The secondary elements consisted of various oxides and metals added to change the colour of the glass.
With the invention of blowing (1st century B.C.), working techniques divided up into two types of production.
Before the blowing technique, heat processes were used that employed an ideally formed container that was made so that the piece could be modelled.
Blowing revolutionized the production of glass objects; indeed, it reduced working times, and brought with it the widespread use of glass objects, which until that time had been done so only by the elite who could afford to do so.
After drawing up a design, the glassmaker would gather up the fused glass gob with a blow-pipe and keep it rotating on a metal plate, the so-called “bronzin”, so as to define its proportions. This stage was very important for the following blowing because it made the glass even and compact, something necessary to the correct expansion of the surfaces. The gob was then lengthened with tongs, by rolling it with a rod that was mounted on the work table, and then went on to the blowing process: this is carried out both by modelling and through the use of instruments with different times and methods depending on the object to be produced. Once the “container” was blown, it was reheated and in the meantime the glassmaker began working on related handles and legs required. Once these latter details were finished they were attached with heat onto the body of the container, making sure of their alignment and symmetry, and then the entire object was reheated.
The blowing technique can be varied using moulds: for example, to get a ribbed effect a cap-shaped glass covering was applied and the composition was blown in a open ribbed mould.
Mould blowing was usually used to give objects special shapes: the moulds were made of clay, wood, stone or metal and could be of one piece or of several pieces, according to the specific shape to be created.
A working technique that dates back to the 16th century is that of “crackle glass”, which created objects with irregular surfaces full of fissures, while still maintaining its transparency. The effect was obtained by putting the semi-finished product from blowing in cold water and immediately reheating it so as to close up the surface fissures. Once the surface effect was stabilized, the piece was blown and modelled into the desired shape.
Among the typical techniques from the 20th century, let us look at four: “incalmo”, “primavera glass”, “pulegoso glass ” and “overlaying”.
Incalmo is a technique that permits the creation of pieces composed of two different pices of different colours: the two single elements are modelled separately and then joined, using an “incalmo”, where they are attached and fused along the edge. This technique is very delicate because the the final fusion point must not be visibile, and as such the two pieces must be modelled so that they fuse together perfectly.
Primavera glass and pulegoso glass are two products created by the inventive minds of two master Venetian glass makers, Ercole Barovier and Napoleone Martinuzzi.
Primavera glass is a simlar product to crackle glass (or glass ice) with a translucent surface covered in fissures; pulegoso glass is opque due to the very high concentration of bubbles of different sizes. Pulegoso glass is made by adding organic substances that decompose and release gas bubbles.
The overlaying technique is ideal for creating pieces with elevated thickness so as to confer a sense of depth to the object. A first glass gob is modelled and blown to give an elementary form of the final shape, and then it is immerged in a crucible containing transparent glass and is taken out to drip off the excess. The piece is modelled and if desired, applications can be used and then it can be newly coated and blown. The pieces play off transparency and colouring of the final layers for a relief effect and one of depth.