Tel Yavne, located in Israel’s southern coastal plain near the Soreq stream floodplain, contains a large Late Roman industrial complex, including the southernmost known primary production site of Roman natron glass. This study investigates the application of stable carbon isotopes (δ13C) analysis, of both glass and slag remains to reconstruct technological aspects of natron glass production, with particular emphasis on fuel selection and firing temperatures.
Isotopic analysis of organic carbon preserved within the glass and the slag reveals a distinct fuel signature. Organic carbon δ13C values in the glass range from -26.7 to -22.6‰, while δ13C values in the slag are consistently lower, around -28‰. These results suggest a strong reliance on C3-type vegetation (trees and shrubs), contributing an estimated 70-100% of the fuel used in firing the glass kilns, and ~100% C3-type vegetation in the slag. This points to a well-organized system of resource management designed to provide the high-energy biomass required for industrial-scale glass production.
Furthermore, this study introduces a novel "isotope thermometer" based on the inorganic carbon isotopic composition of the slag. During heating and cooling, carbonate phases undergo calcination and re-carbonation, resulting in kinetic isotope fractionation. We used the measured inorganic carbon δ13C values in the slag (ranging from -23.2 to -12.1‰) to estimate ancient firing conditions. By applying established fractionation models, our study suggests estimated furnace temperatures of approximately 550-800°C. These results provide empirical constraints on the thermal environments maintained by Roman glassmakers during the melting of quartz-rich sand over several days.
This study demonstrates how combined organic and inorganic carbon isotope analyses can provide new insights into both fuel use and firing conditions in ancient glassmaking.