Murano’s glass centuries-long history boasts a great variety of techniques and their improvements. Techniques can be divided into two main categories: primary processes and secondary processes.
Primary processes are those that occur by changing the initial mix before the melting process in the oven; secondary processes are those that happen after the initial mix has been created and are used to modify the final result by torching and fusing or when cold (“a freddo”) by carving or sculpting. We’ve made a “short” list of the most used and appreciated Murano glass techniques:
Fluohydric acid is used for etching the glass. The effect is similar to sandblasting but thinner and finer.
Avventurina is a translucent glass of a yellow-brown color, in which copper microcrystals are dispersed causing a golden reflection. It is prepared by melting the basic mixture for transparent colorless glass with the addition of cuprous, iron and lead oxides. After the glass melt in the chamber, the cooling process is performed very slowly: the best result is obtained by switched off the oven and leaving it to cool off on its own for several days. Once at the room temperature, the crucible has to be smashed and the “avventurina” is found under a layer of colored glass. This glass found its highest application in Murano in the mid-nineteenth century and it was often used for crafting pieces for royal families of that time.
Neodymium oxide is put in the molten glass, causing a change of color with different lighting conditions: artificial light gives warm tones, fluorescent light gives blue tones, and natural light gives lavender colors.
Cristallo di Murano
Invented by Angelo Barovier in the XV Century, the Cristallo di Murano, or “vetro bianco”, refers to a transparent and colorless glass. This glass is produced with the addition of sodium calcium and, unlike the Bohemian crystal, it is suitable for freehand crafting and blowing.
Invented by Francesco Andolfato in the ’60s, the Doublè technique is used to preserve a golden or silver decoration applied inside a glass work: a decoration is engraved on a transparent glass with the use of a wheel, is then golded or silvered, and ultimately covered with a second layer of glass. At this point, the composition is put into an oven, so the parts join each other, encasing and protecting the decoration.
In use since the XVI century, the “filigrana” (“filigree”) is done by heating up a series of colorless glass rods with a colored inner core which are arranged next to each other on a metal plate and heated up. A cylindrical mass of incandescent glass is then rolled over the rods in order for them to adhere to it. Once this process has completed, the piece is worked on and finished as desired.
Fenicio is a kind of decoration obtained by applying “lattimo” glass around the body of an item in a wavy pattern, which is obtained by using a metal comb called “maneretta” which is passed over the surface. This technique was used by ancient Egyptians and Phoenicians for decorating perfume bottles and cruets, therefore the name.
“Foglia d’oro” is a technique for including a thin 24 karats gold leaf inside of the glass. A small quantity of glass is molten, blown, shaped in a form of a cylinder and rolled over gold leaf laying on a plate in order for to attach.Afterwards, more glass is applied to the item and the leaf is enveloped in the glass. Once the master starts working on this mass, the thin gold leaf breaks and appears as a mix of golden straws.
Foglia d’oro is a technique for including a thin silver leaf inside of the glass. A small quantity of glass is molten, blown, shaped in a form of a cylinder and rolled over silver leaf laying on a plate in order for to attach. Afterwards more glass is applied to the item and the leaf is enveloped in the glass. Once the master starts working on this mass, the thin silver leaf breaks and appears as a mix of silver straws.
A bundle of multicolored glass rods is arranged so that its cross-section displays a certain design. This composition is then heated to its melting point and pulled until the desired diameter. After cooling, the rod is cut into disks of variable thickness, ranging from a few millimeters to a couple of centimeters. These disks can be used in two main ways. One possibility is to set up some murrine on a metal plate, heat them up to their melting point in the kiln and then roll a cylindrical mass of incandescent glass over them, in order for the murrine to adhere to it. Another possibility, largely used for the executions of dishes and bowls, consists in arranging the murrine inside a mold, filling the empty spaces with the glass mixture, and then heating it up to form a single object. After the cooling process, the item is finished off with the use of a grinding wheel.
Millefiori or “a thousand flowers“, is a particular kind of “murrina”, in which the cross-section of the rods used for the initial bundle is made of concentric layers of different colored glass with a star-shaped core. The use of the “millefiori murrina” is the same as the use of the “murrina”.
Molatura is a process for cold-processing glass surfaces, obtaining desired decorations. There are two main methods: one uses silicon carbon tips, has short operating times, but gives rougher results; the other, with the use of copper tips dipped in grinding powder, has longer operation times but gives more accurate and elegant results. Due to its composition, however, Murano glass does not perform greatly with such techniques.
Opalino, is a slightly different version of “Lattimo”, and it creates an effect similar to an opal, an iridescent white-blue stone.
Enamels are applied on the item while cold, and once the decoration is finished, the item is placed in a small “muffola” at 550-600°C where the enamel will fuse without deforming the item. Enamels must fuse at a temperature lower than that of the glass, their colors should not fade at high temperatures, and they should have a coefficient of expansion as close as possible to that of the glass of the item, to prevent breakages during the cooling stage.
The technique of the glass blowing dates back to the I century B.C.E. The mix of glass is put in the furnace until it melts. The blowpipe tip is heated up and is used for taking the molten glass and rolling it on a flat sheet of steel called “bronzin” (marver): this forms a cool skin on the exterior of the molten glass blob and shapes it. The Master then blows air into the pipe, creating a bubble, and if needed more glass can be cast over it to create a larger piece. Once the final size has been reached, the bottom is finalized and the blowpipe is removed from the top to provide an opening or to finalize the piece.
In the “sommerso” or submerged, a layer of colored glass enclosing air bubbles and gold leaves is coated with a colorless transparent layer of a few centimeters.
Using an air compressor, sand or alumina powder is sprayed on the glass item, causing micro fractures that make it opaque. The effect which can be controlled by changing the intensity of the air and the size of the particles, has the advantage, unlike the “etching” technique, of not making use of toxic components.
Glass fusing is a technique used to join glass pieces together by partly melting them: two or more pieces of glass are laid on top of each other or overlapped and are warmed until a temperature of 750-850°C, at which point the glass will fuse onto each other. Glasses with different coefficients of expansion cannot be fused together, for upon cooling the piece would crack.
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