Reflectance spectroscopy reveals mineralogy and preservation of ceramics from the Bidong Shipwreck

Abstract

Shipwreck ceramics are rarely analysed in situ since conventional mineral tests require sampling and jeopardise conservation. This study present the first application of full-range visible-near-infrared (VIS-NIR, 350-2500 nm) reflectance spectroscopy to shipwreck ceramics, analysing 30 sherds from the 16th-century Bidong wreck off Peninsular Malaysia. CIELAB colour space reveals the a*-b* linearity improves markedly from R-2 <= 0.50 on uncleaned surfaces to 0.80 in clean-powder subsamples, providing an objective metric for de-encrustation. High chromaticity and pervasive hematite document dominantly oxidising, whereas a minority of grey fabrics signal reduction firing conditions. Varimax-rotated PCA (VPCA) resolves 18 spectral components in intact sherds but only 11 after cleaning, demonstrating how surface alteration inflates apparent mineral diversity. Diagnostic loadings for illite and Fe-rich pyroxene (hedenbergite) tie the ceramic body to Sukhothai red clays, while copper sulphides and marine carbonates fingerprint post-burial interaction with Cu fittings and seawater. A weak 600-620 nm shoulder tentatively matches lazurite, a blue pigment rarely reported in Southeast Asian wares thus requires micro-analytical confirmation. This rapid, micro-destructive VIS-NIR method provides preliminary information about the salvaged artifacts which can be further correlated with another scientific study for provenance and production techniques interpretation.