By Rebecca Ruger
Authentic and intentionally made purple glass has been produced for hundreds of years, with its popularity rising and falling as with any colored or collectible glassware. "Purple glass" is an umbrella term which may include very pale lavender and medium shades of purple, deep royal purple, violet, and dark black amethyst, among others. Lavender glass is a rather accidental color that has caused a lot of commotion in the glass bottle collector and sea glass world.
Finding that perfect piece of pale purple glass on the beach rightfully elicits at least widening eyes, if not a verbal squeal of delight as well—that’s the sea glass world’s commotion over lavender. It’s one of the few colors you can instantly and reasonably date without any historical hint save the color. You know automatically that this piece of glass was most likely made between 1880 and 1920. If you know that much, then you are also aware that it was originally made to be clear. But, because so much of the sand (key ingredient in glassmaking) contains traces of iron, clear glass cannot be achieved without neutralizing the iron because iron will typically cause some shade of light green, blue-green, or aqua color to be present in glass.
Enter the decolorizer: something added to the batch of glass to counteract the impurities—in this case, manganese. The Corning Museum of Glass says that manganese has been used as a decolorizer since possibly as early as the second century B.C. Using manganese as a purifier was so common (much later) that it became known as the “glassmaker’s soap.”
Apparently, it was not initially known that manganese in glass, affected by exposure to sunlight, UV light, or other forms or radiation, would turn the glass varying shades of purple. The sun causes manganese to oxidize, forming manganese oxide, which is still used as either a colorant or de-colorant, depending on how it’s used, and with what other elements, but also is responsible for solarized purple glass. Hence, glass containing enough manganese may naturally and slowly turn some shade of very light to medium purple after several years of exposure to the rays of the sun.
The dating of "solarized purple glass" or found lavender sea glass has been questioned enough that it warranted several pages and exhaustive research by the author Peter D. Schulz in his book, Baffle Marks and Pontil Scars: A Reader on Historic Bottle Identification. He concluded that regarding manganese use in glassmaking, “popular use seems to have begun by at least the mid 1870s and was solidly in place by 1890” and that a “practical end date for manganese use in all but specialty bottles is about 1920” but gives no definitive reason for the stoppage, though he does note that the end of manganese use generally corresponds with the end of mouth-blown bottle production.
Schulz did, however, address the popular theory held that the United States' supply of manganese largely came from Germany, and when WWI broke out all German imports were severely restricted and glassmakers were forced to find another decolorizer. He argued that Germany was not a significant source for imported manganese to begin with, citing that in 1910 Germany supplied only 2.03% of US imported manganese. Schulz does reference Frank Gessner’s 1891Glassmaker’s Hand-Book, which noted, “the use of manganese has, however, been largely abandoned in European factories in latter years,” and Schulz added, “because it changed color.”
Purple sea glass also came from art glass and pieces such as vases, bowls, tiles, and other glassware made in dark or violet colors. And, a deep-purple glass was used in the manufacture of lightbulb insulators. Pieces of the waste glass from lightbulb manufacturing plants still wash up on the beaches of Lake Erie, and glass insulators from the lightbulbs can be found on beaches around the United States.
The commotion of "sun-purpled" glass in the glass bottle collecting world? Profiteers have discovered ways to speed up the solarizing process by artificial means—irradiated, or with the assistance of a germicidal black light. These purple predators are causing antiquities confusion, damaging the history and integrity of historic glassware, and taking advantage of an uneducated consumer—and reaping the benefits by charging a much higher price online or at flea markets for a vintage or antique bottle that just one day ago was possibly still clear.
But buyer beware: the artificial "purpling" of glass usually causes a much deeper or peculiar shade as a result of strong doses of irradiation. Better safe than sorry: get your lavender glass at the beach.
There's a special kind of glass called neodymium glass that changes color depending on the lighting. In sunlight, it is a beautiful purple. In ultraviolet it is a soft blue or slate color. Learn more about this glass that changes color ›
This article appeared in the Glassing Magazine January/February 2018 issue.