Figure 4.

(a) Infrared spectra of mould H315:58–7 heated to different temperatures. (A) Material heated at 200 °C. (B-C) Material heated at 300 °C and 400 °C. No major infrared spectral changes are detected. (D-E) Material heated at 500 °C and 600 °C. The Al–O–Si absorption at 520 cm⁻¹ is now absent. The Si–O–Si absorption peak at 1033 cm⁻¹ decreases and shifts from 1033 cm⁻¹ to 1043 cm⁻¹. (F) Material heated at 700 °C. The quartz absorption shoulder at 1080 cm⁻¹ increases. A characteristic AlO₄ tetrahedra absorption peak appears at 570 cm⁻¹, likely related to dehydroxylation of Al[O(OH)]₆ octahedra. (G-H) Material heated at 800 °C and 900 °C. The Si–O–Si absorption at 1043 cm⁻¹ decreases further. (b) Infrared spectra of all mould and core samples. These spectra show samples that have not been heated in the laboratory. (A–K) All moulds and one core display clay and quartz peaks without signs of thermal alteration. Note the clay shoulder at 3624 cm⁻¹ and the major clay absorption peaks at 1035 cm⁻¹ and 520 cm⁻¹. (L–N) The remaining three cores do show indicators of thermal alteration. In these samples, the clay peak at 520 cm⁻¹ has disappeared and the main clay Si–O–Si absorption peak at 1035 cm⁻¹ has decreased and shifted toward higher wavenumbers.