The History and Practices of the Glassblowers in Murano

by Lucio Malvezzo

I should like to draw your attention first to this woodcut by Jacobo de Barberi, the Master Caduceus which clearly shows the Isle of Murano. The canal of the glassblowers can clearly be seen in the south crossed by the three bridges.I should like to draw your attention first to this woodcut by Jacobo de Barberi, the Master Caduceus which clearly shows the Isle of Murano. The canal of the glassblowers can clearly be seen in the south crossed by the three bridges.

The old Amurianum, as the island of Murano has been called in honour of one of the ports of Altino, grows in prestige. So much so as to be considered separate now from the other Venetian islands, enjoying a certain liberty afforded by the "Signoria" (ruling class). Such privilege is assigned in virtue of the furnaces that are installed there and consequently the economic importance that Murano has in the social fabric of the Serenissima. By verdict of the Doge and carried over by Doge Tiepolo in 1291, the island of Murano was declared a true and proper industrial area and soon became the capital of glass production in the world as it is today. The Doge is represented by a head of state and flanked by a popular council called Arengo, among the various privileges they are afforded is the so called "Libro d'Oro" or golden book where the names of the most important families are recorded. The icon of the "oselle" or the conservation of the symbol (a rooster carrying a fox on it's back and a serpent in it's beak) is the extraordinary concession that the families of Murano share with the nobility of Venice. The affinity between Venice and Murano is curiously seen in the morphology of the two cities which presents the same public squares, streets, internal canals and even the same "Grand Canal" which runs through it.

It was deemed necessary to construct an order in the productive cycle from the buying of raw materials to the formation of Glass Masters and the preservation of the product. These rules were transcribed from classic latin into a more known language. This transcription took place in the first half of the 1400's with the writing and approval of "Mariegole della arte dei verieri de Muran" (rules of the art of glass_blowing of Murano). The manuscript with a frontispiece illustrating Saint Anthony Abate , patron saint of glassblowers, is bound in a velvet and gold cover. Along with the category of glass-blower who is dedicated to the production of blown or hollowed out glass other categories were added such as; mirror-maker and window-pane maker and in particular rolled glass bound in strips of lead (leaded glass maker). There was also the category of glass flower-maker, bead and "conterie" maker. The name "conterie" or counter is come from the habit of using beads almost like currency considering the quantity and diffusion throughout the countries with which the Venetian Republic traded. All of the glass-making specialties are represented in the internal council which is elected each year and composed of furnace owners and the "Stazionieri", that is to say the sellers who are intrusted with the job of selling the final product.

Hierarchies have grown up around the furnaces that govern the production activities in the "Piazza" (local square) with the "maestri" (glass masters), "garzoni" and "garzonetti" (lackies), "serventi" and "serventini" (trainees) and not least of all the "forcelanti" (glass-cutters) who all depend on the Glass Master and to whom they pay solicitous respect seeing him not only a teacher but above all as mentor.

Murano glass has known moments of great glory over the centuries as well as periods of decline. However it has always been characterized by the Maestri's obsessive search for quality. In fact Murano's pride has always been its aesthetic quality which has often contrasted with its competition and has frustrated attempts at imitation. Throughout the history of art, the hollow blown glass of Murano has forged it's own path, it's strength being in its variation of type and class. From its poly-chromatic glazes and the gold in the cobalt blue of the Barovier cup to the lightness and transparency of its goblets; from the delicateness of the lattice-work to the originality of Murano glass; from the mosaics to the counting beads; from the panes of glass to the mirrors, it all represents the original history of glass. Just as painting and sculpture, interior design, mode and jewelery have become entwined in the history of Murano, due to the versatility of the material to adapt to other forms of artistic expression. Especially today, many artists, even ones such as myself, have felt the need to shape through the knowledgeable hands of the Maestri glass-blowers of Murano, their ideas through the magic of glass, in search of significance in their works of art in the very profoundness of the material's transparency.

The specific characteristics of glass is the way in which it solidifies, passing from liquid to solid by increasing the viscosity and passing from the rigid to the to the solid state which is obtained at a temperature of about 500 degrees C. (centigrade). In this interval of time, the so called "workable thermal interval", the Glass Master can give shape to objects, the finished products of which will retain the rigidity of a solid body while maintaining the transparency of liquid. Glass is composed of about 70% sand and silica which is transformed into a liquid state at a temperature of 1700 degrees C. In order to melt the silica at a lower temperature a "fondente" or "flux" which is used as a melting agent is added. This composition is incisive in glass technology not only because of the economic savings but also because it becomes a protagonist in the characteristics of Murano glass for which it is famous through out the world. The primary melting agent is soda, which has the property to lengthen the solidification time thus allowing optimum conditions in which the Glass Master may work the glass. The higher the percentage of soda the slower the glass solidifies ("slow" glass), in any case the presence of a melting agent must not be excessive, in fact there is an equilibrium that must be respected. If this equilibrium is not respected, over a period of time the glass will bring the flux to the surface and the object will become opaque (in "Muranese" terms it is said that the glass " sputa" spits out the soda). In order to limit this tendency a stabilizing agent is used: limestone or calcium carbonate. Other components which are added to the composition are nitrate and arsenic which have a refining action, facilitating the expulsion of air bubbles and making the fusion more homogeneous. If colours or opaque agents are added to the primary ingredients indicated the famous coloured or opal glass is created. The melting agents come from the Orient. In Plant ash is used as a flux containing a high quantity of potassium oxide and magnesiu. In the Syriac language these substances are known as "allume di catino" and "cenere di soria". It may be suspected that the decision to use this particular potassium based ash which was sanctioned by a Major Council edict of 1306 which prohibited the use of potassium ash made from processed ferns had a political basis. In fact such an edict ensured that the "Galee" (Venetian ships) of the Venetian patriarch would return from the Orient with their holds filled. The plant ash under went a purification process in order to obtain the "sale di cristallo" or the "sale di vetro" or glass salts, which when used together with pure silica and magnesium from Piemonte was the most precious decolorant used by Angelo Barovier in the XV Century to obtain that most precious of Murano glass: crystal. As far as silica is concerned, from 1300 to the present day stones from the Ticino river are used. The so called "cogoli del Tesin are very pure while the "cogoli de Verona are less precious because it makes the glass "zaleto" (yellow). The most famous silica is that which extracted in Istria and along the Dalmatian coast which is quoted in documents as sand from Pola and Lisa.

The most widely used furnace is the "crogioli or slow-baking furnace. These slow-baking furnaces are known by the Glass Masters, in order of size, as "palea", "ninfa" and "curisiol". The composition is loaded into an empty slow-baking furnace in two or three stages.

The first load is placed in the furnace at about 5 pm at a temperature between 1200 - 1300 degrees C. and the last load is placed in the furnace between 9 and 10 pm. The temperature then is raised to boiling point at about 1400 degrees C. in order to allow the air-bubbles to escape from the liquid and allow the amalgamation of the glass. Around 2 or 3 o'clock in the morning the temperature is lowered to around 1200 degrees C. so that at around 7 am when the days work begins again the glass has the necessary viscosity that is required by the Glass Masters. The fusion happens in a slow-baking furnace placed inside of a wood burning "fornace furnace previous to the preparation of the "fritta". This is a pre-fusion mixture of ground "cogoli" (pebbles) and ash which at a temperature of 700 degrees C. becomes a cohesive solid masse. This masse is placed in a slow-baking furnace where after a few days, or sometime after a few weeks the real fusion takes place and forms a workable glob. During the fusion the glob is removed from the slow-baking furnace many times and emersed in water.

In the Master book of 1348 it was written that a certain Bartolomeo Tataro gave a "cacia de fero" (iron instrument) to be repaired, an instrument that was used to pull the fused glass out of the pan and poured into water and then by adding complementary materials bring it back to fusion. This is the first testimony of a technical expedient that the Murano Glass Masters indicated as a practice to "traghetar (cavar) el vero in acqua" remove glass from water.

A modern three tiered furnace

The oven that was used the most in the history of Murano Glass-blowing was the "forno a tre piani" three-tiered furnace (the glass blowers constitution of 1315 ordered that the work be done with a furnace that had three openings "qui habet tres bocas"): one level for a bed of wood, the second level for the slow-baking furnace and the third level was used as a "muffola" or cooling oven which was necessary in order to lower the temperature of the glass very slowly to ambient temperature thus avoiding thermal stress which would make the finished objects more fragile and more likely to break.

To reiterate the refracted interest in innovation which even today pulses in the heart of the Glass Master, it may be enough to say that there exists in Murano a centre of glass experimentation, to which all Glass Masters turn for formulas or suggestions. Even today, those who work with chemical compositions are "L'omo de note" (men of the night). They are among the most curious personalities in the panorama of this sector. They spend their working hours at night in perfect solitude accompanied only by their thoughts, and produce a great deal of work by making their ideas fundamental to the economy of local production. They take care of many different aspects of the glass production, not just the "fondita, or the actual fusion of the glass, but also the maintenance of the furnaces, their destruction and reconstruction after the holiday periods, including the extinction and the delicate job of relighting the fires: the emptying of the slow-baking furnaces, etc. Because of the peculiarity of their work these people have little inclination to talk. For this reason I can't express the difficulty I had in interviewing anyone who would talk to me about his important role and above all about the chemical composition which is a jealously guarded secret. Doro, as my interlocutor is called, after a few minutes of talk promised to write down the formula I asked for and which the next day I would have found on the "scagno" (the Glass Master's work table) del Musta. (I understand how the names may seem strange but in the furnaces family names or registered names are almost never used, preferring nick-names or as they say in dialect "detto" or "so-called". I must say that he was true to his word and I have reproduced here some of his formulas which I will confront with those famous and historic formulas taken from the "ricettario Barbini" (Barbini's book of formulas).

Doro, in his formula book, reproduced above, gives some chemical compositions for coloured glass. As you may note the chemical industry has given a helping hand to these Glass Masters who have always empirically occupied their time with the technological aspects of the question. Naturally I quote here only one of the compositions from Barbini's book of formulas. I have chosen the composition for celeste made on April 11, 1483 and quoted his booklet: refined nitrate white earth red lead from Barileti potash arsenic antimony cotiso de Nitron nitrate There is a curious note that follows the formula: "Butar con fornasa non tanto chalda, mortesina. Sopra questa partita, quando sono stata cota, li ò dato ramina libre 22, a poco alla volta, e poi li ò dato in quatro volte libre altre 300 cotiso di nitrone, e sono venuto un celeste belisimo"(place in a cool oven, almost dying out. When it is baked cover it a little at a time with ramina libre 22 (22 pounds of copper) and then add in four times another 300 pounds of cotiso di nitrate (... nitrate). It becomes a beautiful celeste.)

The basic instruments that are used today for glass work are the same as those found in historic prints. In fact in this print figure A is indicated as "forfex italis tagliante dicta" (Italian hand cutters), figure C is indicated as "instrumentum italis borsella dictum", figure D is indicated as "borsella da fiori italis qua vitrum vellicando diversi generi flores vel ornamenta efficiunt" (Italian glass flower cutter used to make different ornamental flowers...), instruments which the contemporary masters still use today without modification and which are recognized and called: nippers, borsela and borsea for vases.

The most common wood used for the lighting of the furnaces in the beginning was, "gioco forza", Prevalently indigenous wood such as alder and willow. However the Venetian lagoon could not furnish enough wood for the furnaces and requests for wood soon spread to the mainland. In 1285 a law demanded that only "alder" wood be used for combustion even if the word "ontano" indicates generically all burnable wood other than wood used for domestic heating. In fact in documents following the declaration "honarius" the words "lignus sevlaticus" (wild wood) were substituted.

Many things have changed over the course of the centuries. Even so, a common denominator through out the history of glass-making in Murano remains the hand-made production of objects and the traditions that are passed down still today, the fruits of experience of the Glass Masters, or as the Masters say, fruits of the experience of many burns which "le incarna el mestier" marks the trade.