Small glass phial, Egypt, c. 900 AD

Small glass phial, Egypt, c. 900 AD
Dating:800 AD–1100 AD
Material:Glass (all types)
Physical:4.7cm. (1.8 in.) - 10 g. (.4 oz.)

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Links to others of type Bottle

Glass unguentarium, Syria, 100-300 AD
Iridescent blue bottle, Syria, 100-300 AD
Iridescent bottle, Roman world, 1-200 AD
Pyriform glass bottle, Roman, 100-400 AD
Pyriform glass bottle, Roman, 80-150 AD
Translucent glass bottle, Roman, 1-100 AD
  Beneath its lovely iridescent coat, this glass phial was blown from pale green transparent glass. The bottom is flat. The body is square, with slightly concave sides. The shoulder is almost completely horizontal, with rounded edges. The neck starts cylindrical, then flares out into a sort of funnel mouth, presumably providing a good fit for a stopper. The mouth is rimless, apparently flame-rounded.

“Square, thick walled bottles of this kind are very common finds of the ninth to eleventh century CE. They are conveniently stored, and served to transport perfumes and cosmetic oils along the trade routes of the islamic world. Complete examples have been found at Bet She’an and are dated to the ninth century CE- the Abbasid Dynasty” (Israel 2003:365).

Israel Museum #77.31.1033

Glass Iridescence
The iridescent effect that so often enhances immeasurably the beauty of ancient glass was not planned by ancient glass artisans. Instead, it is the combined result of weathering processes and the properties of light. The rainbow effect you commonly experience in daily life, such as on soap bubbles or drops of oil spread on water, stem from the same action: light bouncing on a extremely thin transparent film.

When a glass bottle is new, there is no such thin film. The wall of the bottle is homogenous. But “as glass is exposed to water in its burial environment, some of its [chemical] components can be dissolved by the water and carried away (leached out). This generates a thin surface layer of glass that has a different composition that the undegraded bulk of glass. Often, there is a think layer of air between the corroded surface and the bulk” (Bezúr 1999).

When ordinary white light strikes the bottle, some of the rays bounce off the top surface of the thin film, and some go through the thin film and then bounce off the glass-air interface between the thin film and the underlying glass. When the rays coming back from the bottom of the thin film reemerge into open air, they combine with those that simply bounced off the surface. But since they have been delayed by their additional travel, their waves are no longer in phase (in synch). When these two streams of out-of-phase white light combine, some of the wavelengths cancel out (and therefore those colors disappear), and other wavelengths are reinforced (and therefore those colors become very intense), thus turning white light into vivid random colors.

Glass artists of the late 19th Century, such as Louis Comfort Tiffany, admired the iridescence of Roman glass, and devised ways to produce it deliberately by placing the glass piece while still very hot in an oven filled with vapors (tin and iron chlorides) that would alter the surface and create a thin film of different composition, yielding an iridescent effect that did not require a thousand years to develop.

A more thorough technical discussion of the phenomenon by Aniko Bezúr of the University of Arizona Department of Materials Science and Engineering is available from

Bibliography (on Glass Iridescence)

Bezur, Aniko
1999 Online Notes on Iridescence ( University of Arizona, Department of Materials Science and Engineering, Tucson, AZ.

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