An iridescent appearance is the visual sign of a process of chemical degeneration often characteristic of ancient glass that has been buried underground for many years. This iridescence can also be produced intentionally for decorative purposes, and in this case involves coating the glass with a thin layer of a metallic substance. There are three different ways to do this. The first method consists of heating the piece to spark a chemical reaction in metallic components that are incorporated during the fashioning of the parison. The second consists of fuming the object in vapors issuing forth from tin or silver salts held in a receptacle placed just inside the furnace door until the desired level of iridescence is achieved. These metallic salts can also be mixed with distilled water or alcohol and directly vaporized on the piece when hot. The third method consists of applying a metallic luster, essentially silver or copper based, by painting it onto a cold piece of desired form and reheating it to fire on the shine.

The first two techniques were developed by Thomas Webb in England and Lobmeyr in Bohemia during the second half of the nineteenth century, reaching their aesthetic peak in the Art Nouveau production of the American Louis Comfort Tiffany (1848-1933). Tiffany discovered new colors of surprising subtlety and complex interplay, often including in his pieces fine threads of glass which would be laid out on the marver and incorporated into the parison. The production of Loetz at the same time in Bohemia displays a wide range of decorative variations.

The French artist Fabienne Picaud has shown a great interest in these old techniques which correspond well with her master glass maker sensibilities.

DUNCAN Alastair,”Louis Comfort Tiffany”, Abrams, New York, 1992 BRAY Charles , “Dictionary of Glass- Materials and Techniques”, A§C Black, Londres, 1995