Six giant eyes gazing down on visitors to Blenheim Palace, in Woodstock, have been revealed after five months of restoration work.

The eyes, which measure up to 1.5m across, were first painted in 1928 for Gladys Deacon, the American-born second wife of the ninth Duke of Marlborough.

This was the first time any major work had been done on the panel of painted eyes.

Palace architect Nick Cox, who has been overseeing the work, said: "The north gate is the main front entrance to Blenheim.

"Over the past 80 years, they had deteriorated quite a lot, partially because of exposure to the weather and also water has got through the roof, which caused them to decay further."

An intensive and meticulous procedure has been followed to restore the painted eyes as faithfully as possible, first identifying the original paint used, then slowly building up thin layers of paint used while not obscuring any that had survived. Experts used more than 6,000 sheets of 24-carat gold leaf to restore the gilded areas.

The work is part of a £1m annual programme of repairs to the palace.

Three of the giant eyes are blue, and three brown, and were created by artist Colin Gill.

But the reason for them being painted remains a mystery as there is no written documentation about them.