There are many varieties of ancient glass, spanning over 2,500 years of production and successive cultures, available both on the legitimate antiquities market and in museum collections on view to the public. The vast majority of ancient glass is relatively colorless Roman blown glass (as opposed to core formed, rod formed, mold made, slumped, cast or other techniques), dating between the 1st and 4th Centuries AD, a time when blown glass was produced on a truly industrial scale.
Today, serious collectors of Roman blown glass seem to fall into 2 categories:
1. Those who prefer their glass clear, with minimal iridescence or encrustation from burial in the ground. Here is an example —
2. Those who prefer their glass brightly iridescent, with colorful rainbow effects caused by extended burial in highly acidic or highly alkaline soils. Here is an example —
These are quite understandable reasons behind these choices. Those who prefer clear, relatively unaltered glass do so mainly because they wish to view the artifacts in something as close as possible to their original condition when in use. Many collectors who prefer highly iridescent glass do so because they simply enjoy the sometimes dazzling effects created by nature’s alteration of a man made surface.
The trend even extends to some older museum collections, where curators have selected only the most iridescent examples of Roman glass, hoping for an “Ohhh” and “Ahhh” effect from visitors, while neglecting the importance of displaying Roman glass in a condition as near as possible to the original “working” condition.
It is worth noting that some examples of ancient Roman blown glass were once highly iridescent but were “cleaned” of their iridescent surfaces. This destructive practice, which essentially removes much of the mass of the artifact, was common in the 19th and early 20th centuries. Experienced collectors will often shy away from such pieces, as the stripping away of their iridescent surfaces has left them with a clear surface but paper thin and fragile.
Here are some examples on our website of both highly iridescent Roman glass:
and of relatively clear and unaltered Roman glass: