Reconstructing charcoal formation temperatures in archaeology and volcanology using an automated 532 nm Raman spectroscopy approach

Abstract Raman spectra of charcoal provide structural information that enables the reconstruction of past combustion conditions. We present a calibration method (532 nm laser excitation) for determining charring temperatures from Raman spectra of amorphous carbon, based on Raman band intensity ratios (HD/HG). Using a pine wood reference dataset, we establish statistical criteria for estimating temperature, identifying sp²-hybridization clustering, and detecting oxidative weathering. To ensure reproducibility and accessibility, we introduce our tool CHARM as a free, automated webpage ( https://olivierbrcknr.github.io/charm/ ) for processing Raman data—including de-noising, baseline correction, parameter extraction, and temperature reconstruction. This tool generates standardized numerical and graphical outputs that drastically reduce processing time and analytical bias. Applications to archaeological ceramics demonstrate that reliable temperature estimates of blackened surfaces can be achieved without destructive sampling, while tests on thin section preparations confirm that Raman parameters remain unaffected. Furthermore, our protocol enables statistical analysis of charcoals from volcanological contexts, revealing interpretable temperature ranges despite charcoal modifications by oxidative weathering. Our calibration provides a robust method for consistent, rapid temperature reconstruction of amorphous carbon across archaeological, volcanological, and related fields.