The bull cup from Enkomi (reproduction) Cyprus, 15th century BC

Electrotype reproductions of Angustan Roman Cup before and after restoration ("Enkomi Cup" )

When excavated, this cup was completely covered with green copper corrosion products giving the impression that the cup was made of bronze. X-ray examination revealed the beauty of the cup, showing that it was of inlaid silver.

Since the cup was silver, it was decided to clean it using formic acid. One of the small fragments was tested successfully so the entire cup was immersed in a boiling solution of formic acid for 20 minutes. This removed the green incrustation, leaving patches of cuprite (cuprous oxide) and reduced copper. These latter were removed using wadding soaked with ammonia.

On analysis, the cup proved to be a silver alloy, containing gold (3.4%) and copper (9%), this latter constituent explaining the formation of the green incrustation. The elaborate inlay was in surprisingly good condition and was of gold and niello. Niello, a black decoration, has been used to ornament silver from very early times. It appears to be composed of the mineral acanthite (silver sulphite).

Details

Category:
Experimental Chemistry
Object Number:
1965-17
credit:
Prescott, A.G.

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