They're being interviewed about their $3 million donation, to be announced Thursday, to the State Library of Victoria, but all they want to do is rave about the 161-year-old institution.

Mr Myers, an eminent QC and businessman, loves showing visitors from overseas the famous domed reading room, which he thought "beautiful" in 1965 when studying Latin here as a law student from western Victoria.

In the early 1990s Mrs Myers, now on the library board, was drawn to one of the library's rare-book reading rooms, where the 1839 diary of western district squatter Niel Black detailed pastoralists' brutal treatment of Aborigines. She funded the diary's inaugural publication.

The Myerses cherish the library's Cowen Gallery, which they regard as the keeping place of Victorian history.

They will lead you from portrait to portrait, speaking animatedly about "remarkable" 19th century indigenous leader William Barak; Eureka Stockade rebel leader turned politician Peter Lalor; and escaped convict William Buckley, who from 1803 lived with Aborigines in today's Bellarine Peninsula for 32 years.

Mr Myers says he and his wife are making the $3 million gift to support the library's status as a pillar of society. Also for its egalitarianism. "Anyone can walk in here, not paying anything, and have access to learning".

The usually media-shy philanthropist couple hope going public will inspire more donations, big and small.

The library on Thursday will launch a rare public appeal to raise the last $5.9 million of its $88.1 million Vision 2020 redevelopment that will create 40 per cent more public space.

The state government has contributed $60.4 million, and the Myers' donation is among $21.8 million from philanthropists.

In the 1880s, Mr Myers' ancestors, who were Lutherans from Dunkeld, in the Grampians, were among an army of Victorians whose pennies and shillings helped fund Melbourne's Catholic Cathedral, St Patrick's.

Mrs Myers says: "The small donations can achieve something mighty."

Creative Industries Minister Martin Foley said: "Victoria's creative, cultural and intellectual life is richer for people like Maria and Allan Myers, who are passionate givers whose generosity has opened up opportunities for so many Victorians."

The redevelopment's architectural designs will be released on Thursday.

Details of the appeal are found here http://vision2020.slv.vic.gov.au/