The equipment has taken off some of the paint on the stones

The ultrasound descaling device has removed some of the bright yellow paint daubed on the Rollright Stones on the Oxfordshire/Warwickshire border.

But it is not yet clear how the work has affected the stones themselves.

The unusual idea to use the dental equipment was thought up in an attempt to protect rare lichens on the stones.

The lichens at the site near Chipping Norton are said to date back to 1100 AD.

Splashes of paint have put rare examples of lichen at risk

They were covered in paint when about 70 stones at the Neolithic circle - which itself could date back to as early as 2500 BC - were vandalised on 31 March.

Site manager Dohn Prout told BBC News Online that Wednesday's test showed the equipment could be used to some extent.

"We can well use this as part of the main process of mechanical cleaning - using dental picks and tweezers to lift the paint off the stones," said Mr Prout.

But he estimates it would take two to three days to clean each stone with tweezers - a task that would hopefully be passed on to contractors.

Various chemicals have also been tested but ruled out for fear of damaging the lichen.

"It proves to everybody the care that English Heritage and the trust are taking to make certain the stones are getting the right solution for the long-term," he said.