All millefiori starts with cane -- long, slender rods of glass. To make cane, artists in most cases mix silica with soda and lime -- chemicals that lower the silica's melting point. The raw ingredients go into a giant melting furnace set anywhere from 2,100 to 2,400 degrees Fahrenheit (1148.9 to 1,316 degrees Celsius). After several hours, the ingredients mix to make molten glass.
Artists can color the glass with small amounts of metal oxides. These oxides include cobalt, chrome, red iron, black copper -- which actually makes the glass aquamarine -- and nickel, which makes the glass smoky green. In addition to the furnace full of clear liquid glass, artists who regularly make millefiori pieces may keep pots of molten colored glass inside the melting furnace. Others, who may not make much millefiori, might add the color later using crushed bits of glass, but more on that in a bit.
A single cane of glass starts out either as a glob of colored liquid glass from the previously mentioned pots or a glob of clear molten glass. Whichever the artist decides to use, he or she will stick a long iron rod called a punty or a pontil into the furnace to gather the molten glass on the end. The rod is heated before it goes in the furnace to help keep the glass on the end hot from the inside.
Glass has to stay liquid enough to be malleable, but cool enough to take shape. This typically means keeping the piece's heat above 1,000 degrees Fahrenheit (577.8 Celsius). To do this, an artist will frequently reheat the piece in a dedicated furnace called a glory hole. Molten glass isn't stored in this furnace and is usually kept at about 2,300 degrees Fahrenheit (1,260 Celsius). Whenever an artist needs to reheat a piece, he or she sticks the pontil with the piece on the end into this oven for a few minutes until it's malleable again.
With a glob of glass on the end of the pontil, the artist rolls it back and forth on a metal surface known as a marver. Gravity and the flat metal surface that the molten glass heats help shape the piece. Meanwhile the rolling puts pressure on the viscous glass pushing it in and out into a long, thin cylinder.
Next, the artist puts it all together. Go to the next page to find out how.