Beyond Lightness: Mobile App‐Based Colorimetry, FTIR, and Color Spectroscopy in the Study of Archaeological Burnt Bones

ABSTRACT Heat‐induced color changes in bone can inform burning conditions but are often assessed subjectively. This study tests quantitative CIELAB colorimetry on archaeologically recovered cremated human remains using a smartphone app ( ColorMeter , iOS) and, on a subset, a color spectrometer (Ocean Optics Red Tide USB650), and compares both with FTIR‐ATR crystallinity (IRSF) as a proxy for heat exposure. The app was used to measure 48 calcined bone fragments from the Roman period (2nd–4th century CE) site of Gbely‐Kojatín (Slovakia), alongside an experimental series of bone samples burned at 200°C, 400°C, 500°C, 600°C, 700°C, 800°C, and 900°C for model evaluation. Both methods preserved the overall trend shape with IRSF, but the app data showed the most robust archaeological signal in b * ( p = 0.023) while L * was not predictive and was excluded. In the spectrometer subset, a * provided the clearest association with IRSF, whereas b * followed the same directional trend but was weaker when all samples were included; method comparison indicates the largest disagreement in L *, consistent with illumination sensitivity, while chromatic axes are more comparable. Color values differed markedly between intact bone fragments and powdered bone ash, with a mean fragment–ash Δ E of 19.9. Bone fragment color may be overprinted by surface‐related factors beyond heat exposure. Overall, mobile‐app colorimetry is best suited for low‐cost documentation and screening (especially via a * and b *), ideally validated against spectrometric and FTIR measures rather than used as a standalone estimator of burning intensity.