The Late Antique glass furnaces in the Hambach Forest were working glass - not making it

Abstract

The cluster of Late Antique glass furnaces in the Hambach Forest in the Rhineland, western Germany, has been advocated by K. H. Wedepohl and G. Hartmann in their influential papers as a potential location for primary glassmaking. Here, we re-evaluate and expand the original chemical data and assumptions underpinning this controversial interpretation, and present an alternative explanation for the compositional pattern observed among the glass finds from the site and its wider environment. Glass matching very closely the two main chemical compositions as seen in the Rhineland has recently been reported from numerous 4 th to 5 th century sites in Southern France, Britain, Italy, the Balkans and Egypt, with the same pattern of minor amounts of colorant elements such as copper, tin, lead and antimony, as contamination due to the inclusion of recycled cullet into the batch. The high content in iron and related elements, previously seen as a unique characteristic of the Hambach Forest glass finds, is now recognised as a common feature of these established super-regional compositional glass groups. We identify the majority of analysed finds to consist of HIMT glass, followed by a significant number of série 3.2 glass sensu Foy et al. ( 2003), while only one sample matches glass of the Levantine composition. This sees the furnaces of the Hambach Forest, and the finished vessels excavated in the wider region, fully integrated in the two-tier Late Antique glass industry, where a few eastern Mediterranean mega-producers were supplying their raw glass across the Empire to be re-melted and worked locally into artefacts, including at the cluster of glass furnaces in the Hambach Forest.

Burgi in the Loess Plain of the Lower Rhine Region in Late Antiquity

“…The location of some sites, along with several Type 2 and Type 3 burgi , in the Hambacher Forst suggests that they may have played a role in the glass industry. The late antique Hambach glass industries are well studied (Brüggler, 2009; Rehren & Brüggler, 2020) and the defence of this key industry probably accounts for the cluster of burgi in this zone, either for processing, surveillance, or protection. Although Type 1 enclosures are undefended in a traditional sense, a V-shaped ditch may have acted as a sufficient deterrent to store glass securely before transport and, when coupled with local Type 3 defences, may have deterred would-be thieves.…”

Emerging Glass Industry Patterns in Late Antiquity Balkans and Beyond: New Analytical Findings on Foy 3.2 and Foy 2.1 Glass Types

“…However, several papers have since reported Foy 3.2 type of glasses with higher alumina concentrations. The examples include alumina concentrations of up to 2.38%, 2.51%, and 2.59% [ 7 , 19 , 20 ], so higher alumina concentrations for Foy 3.2 should be allowed. What differentiates Foy 2.1 from 3.2 in such cases is the still higher heavy mineral concentrations and TiO 2 /Al 2 O 3 ratios.…”

“…This time gap has been filled up, with several authors reporting Foy 3.2 assemblages from different periods and places. These include collections from the fifth century Bulgaria [ 7 ], fourth−fifth century Italy [ 19 ], late third−sixth century Italy [ 21 ], mid fourth−fifth century Germany [ 20 ], fourth century England [ 17 ], third−fourth century AD, outlier sample YAS-265 from Carthage [ 10 ], and second−fourth century AD Kosmaj in Serbia [ 4 ]. It seems that in the case of Foy 3.2 type, there is a need to overcome the traditional definition of a compositional group being tied to a single place and time of sand exploitation, and to introduce a definition that would encompass a greater area and longer time.…”

Ancient and Contemporary Industries Based on Alkali and Alkali-Earth Salts and Hydroxides: The Historical and Technological Review

“…Alkali earths, especially calcium, usually counteract this effect to a certain extent and stabilize the glass. Ancient and historical glasses are alkali-lime-silicate glasses because alkali carbonates, such as plant ashes and natron, were the critical raw materials consciously used by glassmakers [31,43,48,[50][51][52][53][54][55][56][57][58][59][60][61][62][63][64]. It is now widely accepted that during the Late Bronze Age, Soda and potash-rich plant ash enhanced by increased lime content was the primary flux additive used to make glass in the ancient Near East [48,50,64,65].…”

“…From the 7th century AC towards the end of the first millennium, the Old World's glassmaking crafts faced a shortage of mineral natron from Egypt and the Levant [51]. This natron shortage led to "re-inventing" the millenniaold alkali flux, i.e., glassmaking in Mediaeval Europe widely adopted the plant potash-ash fluxes [55,57,60,63]. In the 9th and 10th centuries, the art of poly-and monochromatic luster-stained glass became very popular in the Near-Eastern Islamic world [68], see Figure 5.…”