Murano Glass – Glossary

Calcedonio
Calcedonio Glass with multicoloured hues, translucid with opaque veins, obtained by adding to the molten mass, say colourless transparent glass, a pigmented mixture based on different oxides (generally copper, iron, cobalt and tin) and metallic silver that also contains a reducing component (carbon or whatever); the mixture is partially blended with the molten mass and the whole is then mixed after some time. The colouring effect is given both by the dissolution of the metallic oxides in the glass and by the formation of small colloidal particles of metallic silver and copper, smaller than the micro crystals.

Canna
One of the fundamental process of Muranese glassworks. A very large number of types of applications can be found for this, both functional and decorative. The extreme viscosity of the molten glass allows it to be drawn out a certain temperature, starting from the end of the blower’s pipe in long, narrows pipes. When al layer of coloured glass is superimposed over a base of opaque glass it is possible to obtain numberless variants of colour and thickness in relation to how the molten glass is drawn out. Suitably heated rods are used in decorations of vases and figures. All Murano glass factories have always used them extensively with artistic results.

Corroso
Glass whose surface is irregular to the touch due to the use of chemical agents. Technically an “acid” process is caused by the corrosion of the surface of the glass that determines the disgregation of the glass lattice with the formation of a rough layer on the surface. This non-uniform layer causes an effect of partial diffusion and reflection of light. For its execution solutions of hydrofluoric acid and ammonium fluoride in water are commonly used. By varying temperature, time in the bath and composition of the same it is possible to obtain very varied effects. The parts of the glass surface to be kept bright are coated with wax or some other organic protective agent.

Fenicio
Decoration obtained by applying threads of lattimo glass or vitreous paste round the body of the item in a festoon-like wavy pattern, obtained by means of a kind of metal comb called “maneretta” passed uniformly over the surface. This technique goes back to the ancient Egyptians and the Phoenicians to decorate flacons and ampoules.

Filigrana
One of the oldest traditional processes already in use in the XVI century. It is done by applying under heat on the surface of an item a homogeneous series of transparent colourless glass rods, with the core of coloured glass. The rods are previously arranged on a metal plate, they are heated to the melting point and a cylindrical item is then made to roll over them so that they adhere to it. The item is then finished as desired.

Incamiciato
This is a glass consisting of two superimposed layers of lattimo glass and of coloured transparent glass on occasion with the submersion of gold and silver leaf so as to obtain an opaque effect. This is a much simpler execution than that of vitreous paste that involves more complex technical problems, and began to be used during the 20s at almost all the most important factories in Murano.

Incalmo
This is an ancient glass-making technique to make objects consisting of distinct parts joined under heat. Two or more elements of different colours are prepared by modelling them into the overall shape. They are then joined together very accurately and finished as desired.

Lattimo
This is a white milky-like glass in which the opacity is provided by the presence of micro crystals dispersed in the in the matrix separated out when the molten glass is cooled down. The microcrystals do not absorb the light beams but reflect them, and thus determine both the opacity and the white colouring. In the Murano area they consist of calcium and sodium fluorides and they are obtained by adding fluorine compounds such as cryolite or fluorine spar, as well as zinc oxide and alumina, to the glassy mixture. The lattimo was introduced in the XVI century for items decorated with multicoloured enamels, especially refined and rare. It was later used as a complement to other types of process, such as the “reticello “. It fell into disuse in the early Novecento but it was given a new lease on life in the late 20s on the part of the better names of Murano glass factories, such as Barovier & C., Venini & C. and MVM Cappellin & C. The latter was the first to use it without the addition of other colours for a series of geometric vases exhibited at the 1927 Intentional Exhibition of Decorative Arts in Monza. Later, during the 50s, lattimo glass was adopted by almost all the glass furnaces on the island and attained excellent results in figures as well, as was the case of the famous “Commedia dell’Arte” figures by Fulvio Bianconi for Venini & C.

Massello
Full, not blown, glass, processed under heat by modeling a block of glassy mass applied over the tip of a metal rod. This process appears in Murano for the first time in the late 20s on the part of Flavio Poli at the I.V.A.M. furnace of Libero Vitali’s where he designed the first figures in full or “massello” glass.

Mosaico
This kind of glass is obtained melting glass pipes (=canna) of different colour: a set of pipes is prepared on a metal plate according to a given design, heating them up they melt each other. The result is a multicoloured plate that can be used for different complements.

Murrina
This is one of the oldest processes known to man the first examples go back to Roman times. Items made in this way were already existed in the XVI century. Making a murrina consists essentially in preparing a sheaf of multicoloured glass rods, arranged so that its cross-section is according to a predetermined design. It is then heated and when the melting point is reached it is drawn out until the de-sired diameter is obtained. After cooling, the rod obtained in this way is cut up into small disks of variable thickness, ranging from just a few millimetres to a couple of centimetres, whose section has the previously made design. They are now ready to be used in several ways. Their use in the production of several kinds of objects is done in two different ways: The first consists in preparing on a metal plate a set of murrine according to a given design, heating them up and then making them adhere by rotation on the surface of an item with a cylindrical shape, still connected to the blower’s pipe. After this the item is finished as usual, on occasion coating it with a layer of transparent colorless glass. The second more suitable for the execution of dishes and bowls, has the murrine arranged inside a die in refractory material, trying to fill in the empty spaces with glass powder so as to get a homogeneous mass. The whole is then heated as appropriate so that the murrine are welded together to form a single object. After cooling it is finished with the grinding wheel to remove any irregularities that may be due to heating process.

Pasta vitrea
This is a coloured opaque glass whose preparation is based on the same principle as the lattimo glass. In this case, however, white microcrystals are dispersed in a colored vitreous phase. Others, differently, are obtained with coloured micro-crystals dispersed in either a colorless or a colored vitreous phase. In the first case lattimo is used (microcrystals of calcium and sodium fluoride) or white enamel (amore intense white completely opaque even in a thin layer, generally obtained with micro-crystals of arsenic and lead) dispersed in a transparent coloured glass. The white microcrystals, in addition to making the glass opaque, soften the colour of the glass in which they are inserted, that must contain a high percentage of colouring agents. In the second case “cores” are used: these are semi-finished crystalline structures based on lead antimonate or stannate that are yellow or red. These are added to the molten mass just before processing because they are compounds that dissolve easily.

Pezzato (lavorazione a tessere)
This glass is like a patchwork with elements of different colours and is obtained as follows: on a metal plate a series of segments of flat rods, according to a given design are arranged. The plate is heated to take the segments back up to the melting point: at this stage the set of molten fragments is made adhere by rotation to the outer surface of the vase still on the tip of the blower’s pipe. After the pieces have been joined together, they are finished by appropriate smoothing over and modelling.

Pulegoso
Glass with a spongy appearance, with a great many air bubbles, to the point that it is almost opaque. The homogeneous and refined molten mass (with no air bubbles or impurities) is vigorously mixed in with salts (generally sodium carbonate or bicarbonate) that decompose due to the heat and liberate gases (carbon dioxide) dispersed in the form of bubbles of varying diameters.

Reticello
This is a variant of the “filigrana” already known in Murano in the XVI. It is obtained by joining two conical vases under heat, covered externally with thin coloured rods, one arranged clockwise and the other anticlockwise. A network is thus formed with a rhomboid-like mesh. The rods with different thickness, within each quadrangle, cause the characteristic air bubble.

Sabbiatura
This is a process to get the same results as the “acid” process without, however, the latter’s negative aspects, linked with the use of toxic substances. Sand or alumina powder is sprayed onto the glassware with a compressed air device. The impact of the granules on the surface causes microfractures that make it opaque. Sanding is marked to a greater or lesser extent by an appropriate adjustment of both air pressure and granule size. Used mostly on flat panes, this technique has also found application in the preparation of some drawings by masking some of its parts.

Scavo
This is a glass that imitates the effect caused by long periods spent underground, typical of glass objects found during archaeological diggings. During manufacture, a mixture of several powders is dispersed on the surface of the object at a temperature of about 800 C. These adhere irreversibly and give the special effect of opaqueness and colouring. To improve adhesion the piece is heated again. The powder mixture contains melting components (carbonates or nitrates that decompose under heat and act as binders; inert opaqueness (talcum, silica, etc.) other colouring agents. This technique was introduced in the early 50s.

Siderale
This is a glass invented in the early 50s. The procedure for its preparation was as follows: a large concentric-ring murrina was made with two alternating colours; it was then heated again and applied while hot to the item being processed. After a first finishing step, and after cooling, the item still with an irregular shape was modelled and polished at the grinding wheel with an extremely long and delicate operation. With this complex and laborious technique, a limited number of items was made, very rare and refined, that for their essential shape and decor represent the very best Muranese production, with a level of quality that compares well with that of northern Europe.

Smalti (enamels)
Enamels wide spread in Murano since ancient time. While up to the mid-nineteenth century every craftsman made his own on the basis of very particular and jealously kept recipes, it later became fashionable to adopt vitreous enamels produced on an industrial scale. They must have the following features: applied cold to the item during manufacture, they must fuse at a temperature lower than that of the glass, their colours should not fade at high temperatures and they should Ave a coefficient of expansion as close as possible to that of glass to prevent breakages during the cooling stage. Once the decoration is finished, the item is placed in a small “muffola” oven where it reaches a temperature of some 550/600 C to allow the enamel to fuse without deforming the item. In the Novecento this technique was used to make copies of ancient models, but a few exceptions.

Sommerso
This is a glass coated with a thick layer of colourless transparent glass, or with a glass which has a colour different from the one of the backing. It consists of a layer of coloured glass with the inclusion of air bubbles and gold leaf, more rarely with the subsequent application of rods in pulegoso glass, coated with a colourless transparent layer about one inch thick. Many Muranese glass factories extensively took up this technique with very considerable results.

Tessuto
A glass invented during the late 30s it is based on the traditional filigrana, technique with particularly thin rods used in this case, joined one to the other with especially refined alternating colours. On occasion to enhance the surface even further, it was lightly “battuto” at the grinding wheel.

Zanfirico
This is a glass rod executed with the same procedure as the “murrine”. A sheaf of rods of different colours is prepared with a given design, it is heated to the melting point; two metal rods are then attached at the ends of the molten mass while two maestros draw it out and impart a movement of rotation. The fluidity of the material is such that it can be twisted at will to assume its characteristic spiral-like shape inside. This type of object was already known in Murano in the XVI century with the name of “a retortoli ” glass. The current name of “zanfirico” is taken from the Venetian nineteenth century dealer Antonio Sanquirico who proposed this process anew.