Actes du deuxième colloque international de l'association Verre et Histoire, Nancy, 26-28 mars 2009

Marco Verità, Laboratorio di Analisi dei Materiali Antichi LAMA, Università IUAV di Venezia, Venezia (Italy)

Venetian innovations in glassmaking and their influence on the European glass history

∧  TopVenetian glass versus new competitors

In the second half of the seventeenth century, Venice had to meet the competition of other European glassmaking centers that were able to produce glass comparable or superior in quality to the Venetian cristallo. In Bohemia purified potash was obtained by Johan Kunckel in 1676 by lixiviation of the wood ash following the process invented in Venice for cristallo. Stabilized by the addition of a source of lime (chalk), the potash-lime-silica glass became the famous Bohemian crystal, probably clearer and brighter (higher index of refraction), and certainly less expensive than the Venetian cristallo (Kriniki et al., 2003). Lead crystal glass, a clear, colourless lead-silica glass was invented in England by Ravenscroft as an improvement of traditional naturally green or yellow coloured lead glass. Once they were available on the market, these new glasses met great success.

The production of new glasses in other European countries is at least partly connected with the Muranese glassmaking tradition. Among the various coincidences let us mention the escape of glassmakers from Murano from the second half of the sixteenth century onwards to set up glassworks all over Europe. In these factories luxury items imitating Renaissance Venetian glass were produced (façon de Venise glass). The same production methods, shapes and decoration techniques were used in Venice and in the glasshouses in Europe, so that the chemical analyses cannot distinguish between Venetian and façon de Venise glass (De Raedt et al. 2002). The techniques of Venetian glassmaking that had remained secret up to then were partly made public in the first printed book on glass technology L'Arte Vetraria by the Florentine priest Antonio Neri published in 1612. He developed his knowledge on glassmaking in Italy (Pisa and Florence, both centres were strongly influenced by the Venetian glassmaking tradition) and later in the Low Countries. This book was a great success, was translated into numerous languages, and probably inspired some of the experiments carried out by the major inventors of new types of glass in other European countries.

Venice suffered competition also from France, where in the middle of the seventeenth century the Minister Colbert set up the Manufacture Royale des Glaces de Miroirs to produce mirrors of larger sizes and in higher amounts than in Venice. Also in this case the first glass workers arrived from Murano. The French enterprise developed a new technique to make mirrors of larger size (cast-place mirrors, made by pouring molten glass paste on a large surface and then rolling it). In Venice, small mirrors continued to be made out of blown cylinders of molten glass, which masters stretched manually into rectangular shapes. The French cast-plate method of mirror making was adopted in Murano only after the mid-nineteenth century, because it strongly influenced the occupation and status of master glassblowers (Trivellato 2007).

In the middle of the seventeenth century in England, a new type of dark glass bottle, much stronger and cheaper than those available at the time began to be made in large quantities. These dark glass bottles, a real prototype of modern bottles, required raw materials and technology scarcely available in Venice.

The ways in which Venetian glassmakers reacted to these foreign innovations were recently considered by Francesca Trivellato with interesting, unexpected results (Trivellato 2007).

Efforts to renovate their traditional cristallo using new fluxes to reduce production costs while maintaining the high quality of the Venetian luxury glass are described in the contemporary recipe books. For instance, Giuseppe Briati invented a potash crystal glass to counteract the Bohemian competition. Similarly, several Venetian recipes report the addition of significant amounts of lead to the traditional soda-lime-silica glass as well as the use of a new decoloration process using arsenic (or antimony) and potassium nitrates, more efficient than traditional manganese. These attempts were not as successful as expected. Despite the renewal indicated by the documentary sources, the few analyses of eighteenth century Venetian glass available today identify the traditional cristallo made of soda-lime-silica glass.

Despite these unsuccessful efforts, talking of a decline of the Venetian glassmaking is not correct for this time. In the last three decades of the eighteenth century, Venetian glass production as a whole was twice that at the end of the sixteenth century, a period considered a high point for the Murano industry. From the middle of the seventeenth century the Venetian glass production changed substantially. The drop in production of luxury glass was counterbalanced by an increase in the production of window panes, mirrors and beads. Blown window panes and mirror plates (smaller in size than those fabricated in France) continued to be produced in large amounts. They were low in value but in high demand primarily for the Italian markets, but also for the Levant, Europe and North Africa. Beads remained a Venetian specialty. Many European states attempted to manufacture glass beads domestically. Only in Holland, however, were glass beads made in great quantity. In terms of value, glass beads were the most important Venetian glass export. They were shipped primarily to the Levant and Western Europe to be re-exported to Africa and North America (Trivellato 2007).

∧  TopConclusions

In the fifteenth century Venice became the world leader in glass production thanks to a continuous improvement of the glass quality and techniques, which lead to the invention of a new glass, the famous Venetian cristallo. This predominance continued for about two centuries, in which other innovations were introduced: for instance, the invention of new coloured glasses such as the girasole (sunflower, a semi-opaque glass made with lead arsenate) and chalcedony (McCray et al. 1996), and the famous avventurina, a glass containing small metallic sparkling particles (Zecchin P., 2005). These glasses have not been considered in this work. Of important weight in the Venetian success was the great variety of products made along with luxury glass, such as mirrors, window glass, imitation of gemstones, mosaic tesserae, and beads.

The Venetian predominance declined for various reasons, including the escape of Muranese glassmasters and the publication of the first printed book on glass technology. The Venetian glassmakers unsuccessfully tried to oppose the invention of new high quality and cheaper crystal glasses in other European countries at the end of the seventeenth century. No technological innovation took place in Venice to react to the almost industrial production developed in England (bottles) and in France (large mirrors). Contrary to common belief, recent studies demonstrate that these inventions did not lead to a decline of the glassmaking in Venice, but specialization followed. The Venetians continued to make traditional products for which they maintained a monopoly still for long. Mirrors of small sizes made from blown glass, and especially glass beads were produced in the eighteenth century in much greater amounts as compared to the golden age of Venetian glass. The Venetian glassmakers invested more in glass beads, that is, a traditional product that did not require any technological innovation but yielded high profits (Trivellato 2007).