Citizens of the Ancient World seem to have made a solid go at "going green." Ongoing research by Harriet Foster and Caroline Jackson (2010) revealed hints of color deriving from previously blown glass in colorless glass, indicating that Romans often reused glass, adding batches of broken vessels into the raw material from which they fashioned new items. Why is this important? Determining the date and origin of recycled glass can give us clues about the ways in which the Empire was organized, and how changes to the civil order might have trickled down—and surely, we're all interested in trickle-down effects these days.
Later Roman glass predominantly tends toward a blue-green tinge or a colorless variety. Colorless glass was produced in one of two ways. First, through raw materials naturally low in impurities and color-yielding elements, like iron which produced a blue-green color considered natural. Or by using a decolorizer like antimony or manganese, which internally oxidized the element to remove the color. Color could then be produced in controlled measures depending on the ways in which the materials were balanced against decolorizers. According to Foster and Jackson, the quantity and consistent high quality of "'crystal-like' or 'water-clear'" glass suggests strongly that coloring in colorless glass would have been the result of process as "the Roman glassmaker had a profound understanding of colorless glass production" (2010: 3068).
There are two models concerning the nature of the Roman glass industry. The regional model proposes that there was centralized control over raw materials and the process—so there would have been a few large manufacturers, and the glass would have been reworked throughout the empire. The local model holds that resources would have been more freely shared throughout the empire and glass production would have happened in smaller more dispersed factories. The regional model would produce more "pure" examples of glass because presumably factories would be placed near the best sand deposits. In this case, decolorizers would be used rarely (to enhance colorlessness if needed). The local model argues that decolorizers would be common practice as glassmakers would have to contend with the resources at hand.
Widespread recycling does not appear to be common until about 70 AD. This was also a period of military activity for the Empire—Foster and Jackson suggest that one possible explanation for the rise in recycling might have stemmed from material availability. If the regional model holds, then local glassworkers would have had to rely on melting already existing products, finding a creative means of meeting demands in the face of a material shortage.
Perhaps however, recycling was a part of the industry. Melting sand to produce glass would have required temperatures of approximately 2000 degrees-Celcius. Remelting worked glass could be done at lower relative temperatures. For manufacturers who needed to be conscious of fuel sources, this could have been a practical means of participating in industry—an early exercise in sustainable practices?
It does make me wonder if recycling also generated the Roman equivalent of modern-day can collectors. How far does the trickle-down extend?
1. Stern 1999: 451. | 2. For consistency, American spelling is observed in this citation although Foster and Jackson make use of British English in their article. | 3. Foster and Jackson 2010: 3000. | 4. Stern 1999: 451
Photo credit: Flickr, Creative Commons.
Foster, Harriet and Caroline Jackson. (2010). The Composition of Late Romano-British Colourless Vessel Glass: Glass Production and Consumption. Journal of Archaeological Science, 37, 3068-3080 : 10.1016/j.j.as.2010.07.007
Stern, E. (1999). Roman Glassblowing in a Cultural Context. American Journal of Archaeology, 103 (3) DOI: 10.2307/506970