New paint and giltwork is being aged and distressed to suggest that nothing has changed since 1815 when the great rooms were last decorated. Three painters and gilders have been working for three months on the dining room and saloon.
The original paint has been left wherever possible; new paint has been used only where it was completely destroyed.
Andrew Hirst, whose company is doing the restoration, said: 'We have to treat the walls like a giant easel painting because the original colour has faded to at least eight different shades. First we paint over the most badly damaged parts, matching the colours. Then we have to shade off the places where the new and old paint meet using artists' brushes.'
Mr Hirst uses other techniques taken from fine art painting. The white paint used on the woodwork is made with walnut oil rather than linseed oil as pale colours made with a walnut oil base do not yellow. Originally, the walls were white but age has caused the pigment, white lead, to go to a light grey by formation of lead sulphide. The new paint is laced with lead sulphide creating an off-white paint called Uppark white. It should age in a similar way to the original paint.
The main rooms at Uppark were repanelled and decorated in 1815 when Sir Harry Fetherstonhaugh brought in the great landscape designer, Humphry Repton. The style the two men chose baffles experts because it is neither truly rococo nor neo-classical. By chance it was preserved.
At the age of 71 Sir Harry married one of his dairy maids, Mary Ann Bullock. She and her sister, said to be Sir Harry's natural child, maintained the house in the form it was left to them, always repairing and restoring the fabrics and the furniture as if they were custodians of Sir Harry's memory. When the house came into the hands of the National Trust in 1954 it was virtually unchanged.
Wherever possible the original woodwork and plasterwork is being incorporated into the refurbished structure. The carving uses classical motifs such as vines, egg and dart, and acanthus leaves. The original work is so fine and detailed that it costs about pounds 500 a foot to carve the five-inch wide architrave surrounding a door. Gilders are now covering the carving with pounds 5,000 worth of 22-carat gold leaf.
Peter Pearce, the managing agent for Uppark, said: 'We want to avoid a mismatch between old and new without going to the extent of artifice. We would not, for example, want to paint in water stains even if they were there before the fire.'