Last Updated: Nov 23, 2021     Views: 5923

Image: The addition of manganese oxide to glass compositions balances the green tint caused by the presence of iron in sand. Shades of glass bottles included decolorized bottles can be seen in this grouping of bottles in The Corning Museum of Glass Collection: 54.3.10, 70.3.337, 75.4.51, 2003.4.326, and 52.4.244

Hello! Thank you for your question. In historical container glass research, as you noted, the late 19th century until right before WWI is generally the time frame you see cited for the use of manganese as a decolorizer. However, there really isn’t any hard and fast date range, and which decolorizers were used by various companies depended on many factors.

History

Manganese has been used outside of the container glass industry as a decolorizer for much, much longer. In fact, it is generally accepted as the oldest known decolorizer.

According to the article "Solarized Glass" in All About Glass on the Museum's website,

Manganese dioxide is believed to have been first used as a decolorizer as early as about the second century B.C." Glass technology books from the 17th century refer to it as the "glassmakers’ soap" (they believed it scrubbed the batch clean of color). By the 18th century, glass technologists began to speculate that manganese didn’t so much “scrub” the color as balance the green tint caused by impurities in the batch.

By 1913, Eberhard Zschimmer (Jena Glassworks) wrote a thorough description of the most common decolorizers of the day and how they work---specifically manganese and selenium. He touched on a few others (less common) as well.

The Switch from Manganese to Selenium

With improvements in industrial processes, of course, the volume of glass products increased substantially. Automatic bottle machines were developed and their use in the early 20th century began to make manganese a less cost-effective decolorizer. Cost factors tend to drive many changes in glass formulas, with factories always looking for a less expensive alternative to increase profit margins.

By the 1920s, selenium was the primary decolorizer, but manganese was still used for some glasses, according to primary sources from the time.

In the 1940s, articles in industry publications such as Glass Industry and the Journal of the Society of Glass Technologists debate the “best” decolorizer to use during that time but most discuss selenium.

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Comments (1)

  1. Found a bottle west of Lamy, NM some years ago with aluminum, screw-on cap that was beginning to turn purple. A soda company still decolorizing with manganese. This was in the mid-1990s.
    by David Legare on Jun 02, 2019

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