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From Joe Oldaker, Nuneaton, Warwickshire, UK

The makers of the plastic goblet are a bit behind the curve. The colour of the 4th-century Roman glass “Lycurgus cup” shifts .

The editor writes:

• The researchers do mention the Lycurgus cup in their paper (). They suggest that since only it and six other broken pieces found worldwide show the dichroic effect, this may have been due to serendipity rather than to mastery.