Iridescent Glass Jug

Object: JI1733
JIAAW, Cornelia St. J. Lewis Collection

Object JI1733 features a striking iridescent quality that is often found in ancient glassware. Unlike the process of achieving iridescence in modern pieces, the iridescence of this object and others like it was not an intentional design choice made by artisans in ancient times. Rather, iridescent qualities in ancient glassware are caused by weathering on the surface. This weathering process depends on several factors, including the levels of heat and humidity within the burial site, as well as the type of soil that the glass was buried in. Also at play is the chemical composition of the glass itself. All of these conditions determine to what extent alkalis, or soluble salts, in the glass are absorbed by slightly acidic water in the soil, thus, eroding the glass material. 

Once weathered to thin layers, some of which delaminate or even flake off, ancient glassware begins to refract light in ways that resemble a prism. If held at different angles and observed in different lighting, object JI1733 produces a rainbow-like effect, emblematic of the interplay of luminous colors created by its weathered surface.

-Jinette Jimenez ‘21, JIAAW Records and Collections Assistant

Corning Museum of Glass

Glass is found at archaeological excavations in a variety of conditions. The glass condition can range from pristine, where no deterioration is visible, to so heavily degraded that practically all the glass has been transformed into corrosion products. The deterioration of the glass surface is generally known as and the deteriorated area as a weathering crust.

Glass flask | Roman | Mid or Late Imperial | The Met

Cesnola, Luigi Palma di. 1903. A Descriptive Atlas of the Cesnola Collection of Cypriote Antiquities in the Metropolitan Museum of Art, New York, Vol. 3. pl. XCVIII, 6, Boston: James R. Osgood and Company. Myres, John L. 1914. Handbook of the Cesnola Collection of Antiquities from Cyprus. no. 5356, p.


What is iridescence on ancient glass? The iridescence on ancient glass was unintentional unlike what is found on modern Tiffany, Loetz, and Steuben glass. Caused by weathering on the surface, the iridescence, and the interplay of lustrous, changing colors, is due to the refraction of light by thin layers of weathered glass.

Glass perfume bottle | Roman | Early Imperial | The Met

Myres, John L. 1914. Handbook of the Cesnola Collection of Antiquities from Cyprus. no. 5176, p. 509, New York: The Metropolitan Museum of Art. Lightfoot, Christopher S. 2017. The Cesnola Collection of Cypriot Art : Ancient Glass. no. 305, p. 219, Online Publication, New York: The Metropolitan Museum of Art.

The Mystery of Iridescence in Glass

By Anna Pokorska, on 20 May 2019 If you’ve ever wandered through a museum displaying ancient artefacts, chances are you were amazed at the quality and artistry displayed in glass objects of that time. The has some incredible pieces shining with iridescent colours: However, despite the undeniable talents of ancient glassmakers, this particular effect was not intentional or even achieved during production.


Gustavus A. Eisen, Glass: Its Origin, History, Chronology, Technic and Classification to the Sixteenth Century, 2 vols. (New York: William Edwin Rudge, 1927), vol. 1, p. 369, pl. 94. Susan B. Matheson, Ancient Glass in the Yale University Art Gallery (New Haven, Conn.: Yale University Art Gallery, 1980), 74-5, no.