Works by renowned Suffolk artists Thomas Gainsborough and John Constable are part of a previously unseen private collection now on display in Sudbury.
The works are being exhibited in the town's Gainsborough's House museum and include pictures and drawings.
Mark Bills, the director of Gainsborough's House, said the collection was owned by an anonymous collector who was also a keen benefactor of the museum and helping fund its new £8 million extension.
He said the collection was from "a golden age" of British painting.
"Through their loans and their gifts, they are making one of the most important periods of British art open to so many more people," he said.
"The exhibition is a rare opportunity for visitors to see a very special collection displaying one of the great moments in the history of art.
"As one of our most significant supporters of our multi-million pound development they are doing so much for art, the town and the nation's cultural life."
The collection has been built up over 30 years and highlights include Gainsborough's Wooded Landscape with Figures, Cottage and a Pool, Salisbury Cathedral from the Meadows by John Constable, and Elizabeth, Duchess of Devonshire by Sir Thomas Lawrence.
Thomas Gainsborough was born in Sudbury in 1727 and his birthplace in what is now Gainsborough Street houses the museum.
Constable was born just 15 miles away in East Bergholt in 1776.
The exhibition runs until October 27. In the same month work is due to start on building the extension, which is scheduled to open in the spring or summer of 2021.
The extension is on the site of the town's former labour exchange.
Once finished, the landmark three-storey structure will provide spaces for exhibitions, displays and learning with four new galleries showcasing works by Gainsborough, a landscape studio, a community gallery and a temporary exhibition gallery/performance space.
The intention is that the new building will also house the widest collection of art works by Gainsborough.
The whole project is costing more than £8m - a total raised through contributions from private donors and a £4.5m Heritage Lottery Fund grant.
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