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 AvvenTurina
Glass of a yellow-brownish color, translucid, in which copper metal microcrystals
are dispersed to reflect a gold color, formed by devetrification (separation
from the molten mass during the cooling step). It is prepared by melting
the mixture of transparent corlorless glass with the addition of cuprous
oxide and iron and lead oxides. Melting takes place in a reducing chamber
and the molten mass should be cooled very slowly. Traditionally, to obtain
the best quality, once the mass is molten, the oven is switched off and
left to cool on its own for several days. Once room temperature is reached
the crucible is smashed and the avventurina is found under a layer of colorless
oxidized glass.
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Calcedonio
Calcedonio Glass with multicolored hues, translucid with opaque veins, obtained
by adding to the molten mass, say colorless 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 coloring 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 colored glass is superimposed over a base of opaque
glass it is possible to obtain numberless variants of color 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.
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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 colorless glass rods, with the core of colored 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 colored 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 colors
are prepared by modeling them into the overall shape. They are then joined
together very accurately and finished as desired.
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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 coloring. 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 multicolored
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 colors 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
color: 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 multicolored
plate that can be used for different complemets.
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 multicolored
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 millimeters to a couple of centimeters, 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.
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Pasta vitrea
This is a colored 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 colored
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 colored glass. The white microcrystals, in addition to making
the glass opaque, soften the color of the glass in which they are inserted,
that must contain a high percentage of coloring 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 colors 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 modeling.
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 colored 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 coloring. 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 coloring 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
colors; 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 modeled 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 colors 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
colored glass with the inclusion of air bubbles and gold leaf, more rarely
with the subsequent application of rods in pulegoso glass, coated with a
colorless 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 colors. 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 colors 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.
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