Murano's furnaces have burned without interruption since 1291, when Venice's Great Council exiled all glassmakers to the island to prevent fires from consuming the wooden city. The decree transformed a safety measure into monopoly: for five centuries, Murano held Europe's only knowledge of cristallo, a soda-lime formula so clear it rivaled rock crystal. Artisans who fled faced assassination. Those who stayed became nobility, their daughters permitted to marry into patrician families despite guild-class origins. The glass blowing Venice tour tradition connects directly to those medieval workshops. Twenty-three active fornaci still operate on Murano today, their methods largely unchanged from Renaissance techniques documented in Antonio Neri's 1612 treatise L'Arte Vetraria. A maestro gathers molten silica on a hollow cane, inflates the gather with precise lung pressure, and shapes it with wooden paddles soaked in water to prevent charring. The entire sequence—from gathering to annealing—must occur within eight minutes before the glass drops below working temperature. Timing separates apprentices, who train for fifteen years, from masters. Contemporary Murano production balances heritage with commercial survival. After twentieth-century competition from Bohemian and Asian manufacturers eroded market share, the Consorzio Promovetro introduced the Vetro Artistico Murano trademark in 1994, certifying that each piece originates from island furnaces using traditional methods. Factories like Seguso and Barovier & Toso now operate as living museums, offering demonstrations that decode techniques: the sommerso layering that traps color between clear glass shells, the zanfirico rods twisted into spiral canes, the avventurina formula containing copper crystals that sparkle like night water. Most glass blowing Venice tour experiences include boat transfers from Venice proper, since Murano sits 1.5 kilometers across the lagoon. Combined itineraries often add Burano's lace workshops and Torcello's seventh-century basilica, creating a full-day circuit of craft islands. Factory visits typically begin with furnace demonstrations—temperatures reach 1,400 degrees Celsius—followed by showroom access where finished works range from five-euro trinkets to five-figure chandeliers. The €5 demonstration fee supports working artisans, a model that keeps Murano's furnaces lit in an era when cheaper alternatives flood global markets.