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Decorations could be done by engraving, intaglio, overlays, or working on the surface with tongs.
Engraving is done using awls or on the wheel: specifically, the high-relief decorations were done using minimum-waste procedures on very thick glass, with decorative motifs with natural or geometrical elements.
Overlays were carried out by applying filaments or pieces of glass onto the surfaces of hot glass: coloured filaments spiralling around a vase, as was done two thousand years before Christ, or they could be intertwined or spread out in winding curves, while the fragments or pieces of glass were lightly fused on hot glass, and which protrude or which could be flattened down and fused into the glass until it was a coloured area. In particular, bead-effect decorations were carried out by applying pieces of glass onto the surface of the glass before blowing, and during heating they fused. Afterwards, blowing deforms them thereby creating the shape of a long bead-like shape.
Another decoration that was obtained using the same method is called feathering: strips of opaque coloured glass were applied to the surface while the glass was hot and during rotation and blowing the shapes lengthened to form a spiral effect.
A faster decoration was carried out through pinching which consisted of pulling at the surface of the still hot glass and then subsequently refinishing it.
The 16th century saw the introduction of one of the most refined decorative techniques: Filigrana, or Filigree caneworking.
The filigree effect is obtained by starting with normal gob of glass that is going to be blown together with rods of threads of coloured glass and lattimo. These are formed by drawing the gob of coloured glass or lattimo and then modelling it on the bronzin slab until it forms a cylinder. It is subsequently dipped into a crucible containing fused transparent glass, to be modelled on the bronzin slab again. Following this, a second cane is attached to the end away from the “canna di levata” or extracting rod, and two glassmakers pull the canes in opposite directions so as to stretch the gob of glass into a long rod form, which has a coloured centre and an outer transparent cover. After cooling, the rods are cut into the desired lengths and are placed side by side on a plate that is placed in the oven until it reaches fusion point: the plate is taken out and the gob of transparent glass that has been modelled on the bronzin slab is rolled over it so that it attaches itself to the outer surface. This cylinder covered with glass rods is heated again and remodelled on the bronzin slab until it is pinched at one end and goes onto blowing.
Variations of filigree glass are “filigrana a reticello” and “a retortoli” with their network effect.
The first is obtained starting with two cylinders covered with canes that are slowly twisted in opposite directions and thus intertwined and blown, so that the overlapping of the two deformed filigrees going in opposite directions form a fine network effect.
The “a retortoli” effect is carried out along the same procedures of the first technique, but starts off with canes filled with coloured glass that have been twisted together within each other. These canes are made with lattimo and coloured glass: according to the final design they are placed on a refractory plate, heated and a gob of glass previously modelled on the bronzin slab is rolled over the canes. As with the “a reticello” procedure the two glassmakers then pull in opposite directions while turning it at the same time.
With regards to decorations from the 17th century, due to an evolution in techniques of working hard stone, new cutting systems have been developed that use a copper wheel mounted on a wheel.
In an imitation of antique vases, half-way through the 19th century, Venetian glassmakers started to produce murrine glass once more. The procedures to make murrine glass start off with the same canes described for filigree: an initial gob that will be the core of the cane is modelled on the bronzin slab into a cylindrical shape, and then it is covered with a layer of differently coloured glass which when put into a mould has a cross-section in the form of a star. More layers are added and modelled until the desired symmetry is reached, which is followed by the final application of another layer. The cylinder as such is continually modelled on the bronzin slab and then a glass cane is fused to one end of the cylinder which gets pulled in opposite directions by two glassmakers until a long cane with a minimum diameter is formed, while leaving the internal design intact. The cane is then cut into cross-sections with a height of 10 to 20mm to make the murrines. These disc-shaped objects form the base of the composition of the final artefact: they are carefully selected and cleaned, placed on a refractory plate, and the remaining spaces between each disc are filled with pieces of glass canes and are then placed in the oven until the entire composition fuses together.