1. Sir James Thornhill's Baroque ceiling, painted between 1707–26.

Baroque glory restored in Greenwich

The newly restored Baroque ceiling of the Painted Hall in the Old Royal Naval College, Greenwich, one of the largest in Europe, took artist Sir James Thornhill (1675–1734) 19 years to paint, so it is not surprising to learn that it was one of Europe's biggest conservation projects.

Heritage Lottery Funds contributed £3.1million to the £8.5million needed, half a million of which paid for the scaffolding, to create a complete 'floor' just below the ceiling where conservators could walk freely within easy arm's reach of the 4,000sqm painting. 'The sheer scale and complexity of the project meant that we were constantly seeking innovative solutions – from the carefully developed conservation techniques to the design of the vast internal scaffolding, which had to be fully accessible for the visiting public,' says Project Director William Palin.

The oil paintings were made directly on to goat-hair plaster, which still proved to be in a remarkably stable condition. Too high to be seen from the ground, the graffiti of some 30 previous restorers was discovered, a reminder of more than three centuries of almost continuous cleaning. In the 1950s, during the last restoration, 15 coats of varnish were removed.

Thornhill was compelled to work 60 feet above ground, standing on a wooden tower that was moved around the Hall. He was paid £3 a square foot for the ceiling painting and £1 for work on the end walls. While he was carrying out the commission he became the first British artist to be knighted.

2. The Old Royal Naval College in Greenwich: the Painted Hall is beneath the dome on the right.

Stephen Paine of Paine & Stewart, whose company undertook the restoration, says: 'The close proximity of the paintings to the platform scaffold revealed the immense skill with which Thornhill executed this magnificent scheme and it is to be hoped that, after this conservation programme, his importance as one of the most pre-eminent artists in British art can once again be recognised.'

Completed in 1705, the Painted Hall was built for naval pensioners by Sir Christopher Wren (1632–1723) – as a companion to Chelsea Hospital for army pensioners. Thornhill was commissioned two years later by George I (r 1714–27) to paint scenes that celebrated England's naval power and mercantile prosperity, as well as its new Protestant royal lineage, starting with William and Mary in 1688. William II is depicted trampling on the cowering figure of tyranny, a thinly disguised Louis XIV. The Hanoverian kings were famous for ill-treating their wives and, when Thornhill asked George I where he should position his wife, Queen Sofia, in the painting, the king replied, 'Under the carpet for all I care'. So there, beside the figure of Thornhill himself, is a small royal hand poking out from under a carpet.

The Painted Hall was visited by thousands in 1806 when the body of Admiral Nelson lay in state there after the Battle of Trafalgar; it then became a maritime art gallery before the paintings were moved to the Maritime Museum in the 1930s.

The Hall's original purpose was a mess for the pensioners, but they soon moved to the undercroft, which was warmer and closer to the kitchens. The undercroft, which has also had a makeover, is to open to the public for the first time, with a shop, café and visitor centre.

The Old Royal Naval College is part of Maritime Greenwich, which was designated a Unesco World Heritage Site in 1997.

• The Painted Hall opens to the public on 23 March, 10am to 5pm daily (www.ornc.org).
Roger Williams