Culture

From Ancient to Art Nouveau

Decay makes beauty in an ancient bottle.

By Clay Cansler | July 13, 2017

A Roman bottle (ca. 200 CE) showing iridescence from weathering.

Science History Institute

The whirl of color and iridescence on this Roman bottle (ca. 200 CE) is the product of a thousand years of weathering. Acidic soil conditions slowly leached alkali from the glass. The alkali collected in layers that eventually separated and flaked off, leaving behind slivers of almost pure silica. The opalescent rainbow we see today is light scattered by these many slices of silica, says Stephen Koob, chief conservator at the Corning Museum of Glass.

At the most basic level, glass is made of three components: former, stabilizer, and flux. The former typically makes up the bulk of the material in glass, and the most common for­mer has always been sand (silica). Stabilizers give glass strength and make it water resistant; lime was the most common stabilizer used in ancient times and remains so today. Finally, the flux lowers the melting point of the sand and allows the glass to be shaped. It is also the alkali pulled away by acidic soil and water over time.

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Science History Institute

CHF’s ancient specimen was found in Israel, where glassmakers typically used natron as their flux. Natron is a naturally occurring mix of soda ash and baking soda mined from dried lake beds in northern Egypt. (It is also why we abbreviate elemental sodium as Na in the periodic table. Na is short for the Latin natrium, which is derived from natron.) Ancient Egyptians used natron in all sorts of ways: as a soap, an insecticide, an antiseptic, and even as a way to dry out their mummies and protect them from rot.

At the beginning of the 20th century, artist Louis Comfort Tiffany turned the natural aesthetic of decayed Roman glass into a fortune. The son of a successful jeweler, Tiffany started out as a landscape painter before turning his attention to home decor and glass art. During travels to Old World museums the young artist was taken by the beauty of weath­ered glass and wanted to incorporate the strange effects into his stained glass. Eventually he opened his own glasshouse in Queens, New York, and began producing his Favrile line of art glass. Tiffany’s chief chemist, Arthur Nash, mimicked the opalescence of ancient bottles by mixing and spraying molten glass with various inorganic colorants, such as silver nitrate and uranium oxide. When the material was exposed to heat and low-oxygen conditions (called a reducing atmosphere) in the kiln, the surface took on different types of metallic luster, depending on the colorants used.

These processes were kept top secret. Nash wrote his recipes in code and hid them in a locked leather notebook. He guarded his recipes so closely, his son later recalled, that even Tiffany didn’t know the formulas.