Historic saltpetre of British Indian origin: An isotopic and socio-economic analysis

High-grade, historic saltpetre (KNO₃) for gunpowder manufacture amounting to more than 50kg was excavated from the store house of the Nagasaki Prefectural Tsushima Museum of History and Folklore (NPTMHF), located at western Kyushu, Japan under very well preserved conditions. It represents the largest economic specimen in the world-wide mineral collection. High precision ¹⁴C dating by accelerator mass spectrometry for associated wooded chips of the container together with the Japanese traditional wrapping paper shows raw radiocarbon ages of 1868±15 and 1880±20, respectively, corresponding to the maximal demand for saltpetre in the modern Japan. Distinctive δ¹⁵N_{nitrate-nitrogen} values (+13‰) and ⁸⁷Sr/⁸⁶Sr ratios (0.715) are indicative of the exotic origin, at the time when the British Indian product under the monopoly industry of the Empire of the United Kingdom prevailed. The nitrogen isotopic signature (δ¹⁵N=+17‰) is comparable with two types of authentic Bengal saltpetre specimens from the Natural History Museum (NHM) in London donated in the early 1850s. Rough saltpetre once produced in the Ganga River Valley was subject to re-crystallization process in the United Kingdom, as evidenced by shifting ⁸⁷Sr/⁸⁶Sr ratios from 0.722 (rough saltpetre) to 0.708 (refined saltpetre). A close examination of historical documents (1865 to 1870) directly relevant to the importation of British saltpetre into Nagasaki harbor during this time was made for both the Japanese (treasure documents kept in the custom house at Nagasaki) and the United Kingdom sites (parliamentary papers). Combination of geochemical and socio-historical evidences elucidates the maritime route of world-wide saltpetre marketing at this time.