Vietnamese (15th century) blue-and-white, Tam Thai and lustre porcelains/stonewares:: Glaze composition and decoration techniques

EDS, X-ray fluorescence, Raman spectroscopy, thermal expansion-shrinkage measurement and scanning electron microscopy were applied to determine the elemental components, structural phases and glazing temperatures of the transparent glazes, blue underglaze and overglaze tam thai (including gold-like lustre) decorations from the 15th-century Vietnamese porcelains/stonewares found at the Chu Dau-My Xa kiln site and in the Cu Lao Cham (Hoi An) cargo. The ancient technology for colouring the glazes is discussed. The various blue tones in the underglazed decor result from cobalt-containing manganese ore, with the intentional addition of iron oxide. The overglaze copper-green and the gold-like lustre were obtained by dispersing copper in lead-based glass. The red colour was made using hematite dispersed in lead-rich flux.