In order to gain insight into the chemical structure of the pigment, we surveyed the NMR literature for likely candidates. The broad signals centered at 116.8 ppm and 148.5 ppm in the C ssNMR spectrum of the HGA-derived pigment sample are characteristic of carbon atoms situated in phenol-like rings, in agreement with hydroquinone-like or HGA-like ring structures . If benzoquinone rings are present in the chemically-derived pigment, it should exhibit C signals at 136 ppm, which we clearly did not observe (Fig. ).