The specific feature of glass, the one that distinguishes it from other materials, metals for example, is the way in wich it solidifies, that is, how it passes from the liquid state at high temperatures (1400 °C) to the rigid solid state. The solidification in glass take place slowly as the temperature decreases. It passes from the fluidity of the melted substance with ever increasing viscosity to the rigidity of the solid at about 500 °C. It is in this interval, called in the fact the working time when the glass is feirly malleable, "pastoso"(paste-like) and before it hardens completely, that the glass master can shape the object which will have all the ridigity of a solid body but recall the liquid by its trasparence.
obtain the liquid the molten substance wich on solidifying, will have the characteristics
of glass, one starts from raw materials, of which about 70% by weight is made up of sand
or silicates. The other raw materials are added to keep the temperature of fusion. The
substances which allow this lowering of temperature are thus called "fondenti"
(flux or melting agents). The materials are:
With these raw materials the transparent colourless glass known as "Murano crystal" was obtained from about 1450 on. The homogeneity and the transparency of fine blown Murano glass today are definitively guaranteed by the purity of the raw materials and glass-melting methods, that is the possibility of reaching fournace temperatures of over 1400 °C, thanks to rich fuels such as methane. At these temperature is easily reached through fuelling by methane, permits working cycle of 24 hours. The mixture of raw materials is loades two or three times into the initially empty pot. The first load goes in about 5pm, at a temperature of 1250 °C to 1300 °C. The last at 9 to 10pm and afterwards, the temperature is raised to 1400 °C to drive any bubbles out of the liquid and to let the glass become homogeneous. At about 2am it is ready and the temperature is lowered to 1000 - 1100 °C. At this temperature, the glass will, at 7am have the viscosity necessary for working.
THE GLASS OBJECT ONCE COMPLETED.
In more recent times, from the expirience of the nineteen thirties, we have blown glass with thick walls, and heavy glass objects. They were conceived as an alternative to the traditional blown glass, but in reality one can see its Venetian nature in that is modelled when hot. Some glassmakers have had noteworthy results here, and in the search for particular results within the body of the glass, such as the superimposition of glass layers of different colours ("vetro sommerso"), the inclusion of fine gold or silver leaf, and design of air bubbles, while the surfaces can be gaven a treatment of irridescence or corrosion. Hot working in the furnace covers a vaste range of products including the decorative objects sector in which there are vases, plates, bowls and sculptures in either blown or solid glass, table glasswear in ancient and modern styles and as a fairly important entity, lamps. In the lighting sector the production of the traditional eighteenth century chandelier continues without interruption. Decoration in coloured enamels and engraved gold leaf, which brought Murano glass prestige in the past, is still used both for modern models and for reproduction of ancient ones. Even now a decorator is proud of being able to reproduce a skilful copy of the "Coppa Barovier" or some other famous fifteenth century goblet. As far as the engraving is concerned, the fine line, done with the diamond, point is the one which, from the first half of the sixteenth century enhances the lightness of Venetian blownglass.
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