We
analyzed a red paint sample from the surface of a gold mask
excavated from a Middle Sicán elite tomb in Peru. The mask
covered the face of the principal male and dates from ca. 1000 AD,
a period when many painted precious metal objects were produced. The
paint’s inorganic pigment was identified more than 30 years
ago as cinnabar (a mercuric sulfide scarlet-red to brown-red mineral),
but the identity of the effective organic binder remained a mystery.
Fourier transform infrared (FTIR) analysis of the sample indicated
a proteinaceous composition, and no lipids were recovered from an N,O-bis(trimethylsilyl)trifluoroacetamide
(BSTFA) derivatized extract of the sample analyzed by gas chromatography–mass
spectrometry (GC-MS). Proteomics analysis by nanoLC-MS/MS identified
unique peptides in the sample, which were matched to human blood and
bird egg proteins via Uniprot database searches. These included immunoglobulin
heavy chain, immunoglobulin G, serum albumin, and ovomucoid. Cinnabar-based
paints were typically used in the context of social elites and ritually
important items. The presence of human blood would support previous
ideas that red cinnabar paint may represent “life force”
intended to support “rebirth”. As the red paint sample
came from the first scientifically excavated Sicán gold mask,
the results suggest a method to authenticate similar unprovenanced
masks now in private and museum collections. Proteomics data set identifier .
We analysed corrosion from a copper bowl dating from the Roman period (43–410 AD) found in a farm in Kent, UK. Despite its relatively good condition, the interior and exterior surface of the object had areas of deterioration containing green and brown-coloured corrosion which were sampled for characterization by a multi-analytical protocol. Basic copper chlorides atacamite and paratacamite were identified in the context of mineral phases along with chlorobenzenes in the green corrosion. Chlorobenzenes are common soil contaminants in rural areas from the use of pesticides, many of which were banned more than 50 years ago. Here we show that their presence is associated with accelerated corrosion, and this provides a threat to the preservation of archaeological metal objects in the ground.
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