Amethyst - Colored

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

💡 If you find purple glass in a historical context, it likely dates to the turn of the 20th century and was originally crystal clear before being "sun-colored" by decades of exposure. APPENDIX E: CULTURAL RESOURCE ASSESSMENT Colored Amethyst

The purplish hue is the result of a specific manufacturing process: When exposed to sunlight (UV radiation), the manganese

This report examines glass, a specific type of historic artifact frequently used by archaeologists to date sites from the late 19th and early 20th centuries. Executive Summary APPENDIX E: CULTURAL RESOURCE ASSESSMENT The purplish hue

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:

SCA glass is a critical diagnostic tool for cultural resource assessments and archaeological surveys.

Because manganese was the primary decolorizer used specifically from 1890 to 1920 , the presence of SCA shards helps researchers pinpoint the age of a historical site.