As anyone knows who has tried to sort their green beach glass by color, there seems to be an endless number of greens. The reason why is actually pretty simple.
The main ingredient in glass is sand, and one of the metallic compounds almost always found in sand is iron oxide in the form of ferrous iron. In normal concentrations, iron oxide gives otherwise clear glass a bluish-green tint. In higher concentrations, it gives the glass a yellowish-green or even dark green tint. Glass left untreated, or “natural” glass, therefore, usually ends up with a greenish tint.
Depending how thick the glass is, this green tint might not be noticeable. However, thicker pieces might appear a deeper green.
Glassmakers created their own proprietary formulas for adding compounds to natural glass to achieve desired green colors for their glass. Variations still occurred due to differences in the concentrations of impurities in the ingredients, different temperatures when melting the glass ingredients, and imprecise measurement of additives.
Put all of these variations together—impurities, thickness, temperature, measurement—and then add in different lighting situations, and you start to get an idea as to why there seem to be so many different colors of green glass. So, instead of trying to sort each and every color of green glass into its own jar, embrace the variety of colors and maybe even just let them all mix together.
This article appeared in the Beachcombing Magazine July/August 2019 issue.