History Murano Venetian Glass Art

The fluxing agents of Muranese glassmakers. Part 1
The first reference in Venetian documents to "allume" (vegetable ash obtained by burning some coastal plants) used as a fluxing agent is in 1275, when the Republic Council prohibited the exportation of glass, ash and sand. This was the first out of a long liet of prohibitions issued by the Senate in order to protect glass art. Apart from a period of a few decades in the XV century, when Verona, Bergamo and Brescia were permitted to receive a small amount of "allume" per year, such a prohibition was valid until the serenissima fall. The last reference comes from the glassmakers' Capitolare of 1766, where the ter "allume" has disappeared and the fluxing agent is distinguished in "rocchetta" (bulk ash) and "polverino" (a less valuable powder ash).

The fluxing agents of Muranese glassmakers. Part 2
The 3rd recipe of the munuscript 797 in the State Archives in Florence mentions "allume catino" and "soda di Soria" togeter with Provençal ash used as fluxes to make "cristallino". Half century later, Vannuccio Biringuccio wrote thet ground pebbles and "cali" weed ash (of different origins) should be used to make glass. In 1544 the Senese naturalist P.A.Mattioli wrote that the "kali" weed could be found also on Venetian shores and Bernardo Cesio stated in 1636 that "allume catino" could be obtained from a plant growing o coastal areas near Comacchio. Towards the ed of the Cinquecento the Muranese glassmakers began to use the Spanish "barilla", even if it gave the glass a light blue colour, as pointed out by Antonio Neri

The fluxing agents of Muranese glassmakers. Part 3
Saltpetre entered the scenery of the Muranese glassmaking in the last decade of the seicento and soon became an indispensable element for the production of Bohemian style crystal glass and most of enamels and rods for bead making. In order to enable the Muranese glassmakers to faceforeign competition, since 1739 the Venetian Republic allowed many glassmakers (Giuseppe Briati as first) to obtain saltpeter (used to prepare gunpowder) at cost price

The fluxing agents of Muranese glassmakers. Part 4
In the eighteenth century, Muranese glassmakers used potassium nitrate as a flux for high-quality glass and they tried to introduce potassium carbonate (with not as good results), which they obtained from wood like german glassmakers. The "ash from Sicily" was the main flux used in Murano between in the second half of the 18th up to the end of the 19th centuries. Yet, its costs and the difficulties of supply induced the glassmakers to use local raw materials, often of poor quality. They used brickklin ash for sheet glass manifacturing, the main activity on the island in the 18th century. It was not purified and the sheets were opaque, with plenty of bubbles and a low resistance. The Venetian Republic supported the cultivation of "roscani", a kind of coastal and lagoon plants from which ash of varying quality could be prepared, but it was used only for common glass products

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