Raman analysis of red-brown and gray shards from 16th and 17th century Portuguese shipwrecks

Abstract

The artifacts under investigation (three red clay shards, two gray clay shards and a red clay teapot) are from the J A Van Tilburg museum at the University of Pretoria (UP). The large red clay shard was recovered from the 1552 Portuguese shipwreck, São João, found in the region of Port Edward, South Africa. The other shards were recovered from the 1622 Portuguese shipwreck, the São João Baptista, which sank around Kenton-on-sea off the South African coast. The results from these are compared to those obtained from the analysis of a red-brown teapot. The oldest of this type of teapot was made in China during the second half of the 18th century. Raman spectroscopy has proven to be a useful tool for qualitative determination of the composition of these clay artifacts. The red clays were characterized by the presence of hematite, kaolin, quartz, amorphous carbon and aluminosilicates. The results of the clay teapot differed from those of red clay shards in that no quartz Raman bands were observed for the clay teapot. The gray clay shards were characterized mainly by the presence of quartz, kaolin, amorphous carbon and aluminosilicates. The presence of mullite in all samples could not be ascertained unambiguously using Raman spectroscopy. The pigments found in the investigated samples are hematite (α-Fe₂O₃) (for red samples) and amorphous carbon (for both red and gray samples).