Murano glass makers held a monopoly on quality glass making for centuries (reference: Venice origins: Unique glass Christmas ornaments). They developed and refined many technologies including crystalline glass, enameled glass (or smalto, which is a material made by fusing powdered glass to a substrate), glass with threads of gold (aventurine), multicolored glass (millefiori), milk glass (lattimo), and imitation gemstones made of glass. Today, the artisans of Murano are still employing these century old techniques, crafting everything from contemporary art and glass figurines to glass chandeliers and wine stoppers. How far back does hand blown glass Christmas ornaments go? Let me know if you find the answer, I have yet to!
The process of making glass is a rather complex. Most Murano glass art is made using lamp working techniques which require a gas fueled torch to melt rods and tubes of clear and colored glass. The glass is made from silica which becomes liquid at high temperatures. As the glass passes from a liquid to a solid-state, there is an interval when the glass is soft before it hardens completely. This is when the glass master creates the shape from the material.
Other raw materials, called flux or melting agents, soften at lower temperatures. The more sodium oxide present in the glass, the slower it solidifies. This is important for hand working because it allows the glass maker more time to shape the material. The various raw materials that an artisan might add to a glass mixture are sodium (to make the glass surface opaque), nitrate and arsenic (to eliminate bubbles) and coloring or opacifying substances.