Certain pieces of Kim’s art and ornaments feature glass that has a lavender or purplish hue. These pieces of glass are fairly rare to find in the river and range in shades from light amethyst to deep purple.
While some glass was intentionally turned purple by adding higher concentrations of manganese to the glass-making process, it was more common prior to the First World War for lower levels of manganese to be used to decolorize and clarify clear pressed glass. While the addition of manganese appeared to work well to remove the greenish tint that naturally occurred when making the glass, years of exposure to ultraviolet light (such as sunlight through a window pane) resulted in a chemical reaction to the manganese which slowly converted it to sodium permanganate, a compound with a characteristically purple color.
Longer periods of exposure to UV light would cause more of the manganese to react, resulting in darker shades of purple. Window panes that had turned slightly purple over many years were highly prized as antiques and, as one might expect, quickly led to the discovery of a method to speed up the process to make a quick buck.
For decades now, the practice of irradiating glass with electromagnetic radiation, such as ultraviolet light or the high energy particles produced by gamma rays and electron beams, has been employed by “antique” dealers looking to charge considerably more money for plain clear glass than it would otherwise be worth. Methods of quickly achieving the desired darker purple hue include the use of germicidal UV lamps or simply leaving the pieces outside in particularly sunny regions of the United States (these were sometimes known as “desert glass”).
In researching this topic I’ve come across several articles by collectors and dealers of EAPG (Early American Pattern Glass), all expounding the harm done to the antique glass market by the practice of artificially coloring relatively new glass just to hike up the price. Not only was the practice dishonest by tricking the buyer into thinking their piece was much older than it actually was, but it also made determining the age of any piece of purple glass in the wild much more difficult as the degree of purple tint could no longer be used as a guide to assess it’s age.
Here are a few examples of those articles:
- This color purple – an unnatural disaster
- Fake and Altered Insulators: Artificially Induced Colors
- The Truth About “Sun Colored” Glass
- Irradiation Changes Color of Glass – Real or Repo (this one goes into some technical detail about the process)
At any rate, pieces of river glass found with varying shades of purple are very rare to find, at least in our corner of the Aroostook River. The few that we have were found over several years of scouring the river bed. A method for testing the glass for authenticity (meaning, glass that was sold clear and acquired a purple color naturally over time) isn’t readily available to us, so we don’t really know how old each piece might be with any certainty.
However, authenticity by adherence to an established process isn’t really what gives a piece of river glass its value. To us, each piece of glass carries its own story that makes it unique, and any additional bits of history (like post-World War irradiated glass scams) just add to its uniqueness and character.