Manufacturers added manganese oxide to "mask" the natural green or aqua tint caused by iron impurities in the sand used for glassmaking.
Around the start of World War I, the supply of manganese (largely imported from Germany) was cut off. US manufacturers switched to selenium , which turns a straw or amber color when exposed to the sun, marking a distinct shift in the archaeological record. 3. Common Artifact Types Archaeologists frequently recover SCA in the form of: Colored Amethyst
When exposed to sunlight (UV radiation), the manganese undergoes a chemical change, shifting the glass from clear to various shades of amethyst or violet. 2. Archaeological Significance Manufacturers added manganese oxide to "mask" the natural
The purplish hue is the result of a specific manufacturing process: the manganese undergoes a chemical change