Technical investigation of 15th and 19th century Chinese paper currencies: Fiber use and pigment identification

Herzberg staining, a quick and convenient tool for distinguishing non-wood fibers from wood pulp, and Raman spectroscopy were employed to investigate three paper currencies issued under the reign of the Chinese Ming and Qing Emperors between 15th and 19th centuries - da ming bao chao (AMS C-14 Date: 1410-1435AD, +/- 1 sigma) from the Early Ming Dynasty (1405-1433AD) and da qing bao chao (1859AD) and hu bu guan piao (1854-1858AD) from the Late Qing Dynasty (1840-1911AD). Fiber staining and microscopic examination revealed a predominance of bast fiber from probably mulberry trees and very few cotton fibers (supposed to be environment contamination) in da ming bao chao; fibers in da qing bao chao and hu bu guan piao turned out to be quite pure, which are also bast fibers but very likely came from ramie and paper mulberry trees, respectively. Raman analysis of red, blue, and black pigments on the investigated paper currencies showed that: (1) The reddish seal on da ming bao chao is not a vermilion (HgS) paste, as it is traditionally assumed, but instead a red lead (or minium, Pb3O4) one. The red pigments on both da qing bao chao and hu bu guan piao are vermilion (HgS). (2) Prussian blue (Fe7(CN)1814-16H2O), a Western pigment, was identified as blue on both da qing bao chao and hu bu guan piao. (3) The black pigment on all these three paper currencies is amorphous carbon from soot. (4) Raman analysis of evenly distributed white pigment particles among the fibers in da qing bao chao confirmed the use of calcium carbonate (CaCO3) as coating pigment or fillers. Both microscopic examination of stained fibers and Raman analysis allowed, for the first time, the understanding of fiber and pigment use in producing ancient Chinese paper currencies. Copyright (c) 2013 John Wiley & Sons, Ltd.