Art restorer Amy Griffin, from the Simon Gillespie Conservation Studio, says that it should be possible to remove the graffiti without damaging the original painting.
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A number of families were on board the service from London Euston to Stoke. One family left the train early to escape the abuse.
She's called Amy, and was visiting a hospital.
The victim is believed to be aged in his 60s and though next of kin have been informed, formal identification has not yet taken place.