BEN Gascoigne has spent much of his life peering at the stars from Mount Stromlo Observatory outside Canberra.

His wife, Rosalie, found beauty and meaning in mundane things, discarded and strewn about beneath the gaze of most of us: old soft-drink crates, beer cans, reflective road signs.

Rosalie is gone now, but those lowly objects she treasured and to which she granted new life have become close to priceless, held in every significant art collection in the nation.

Yesterday, Ben Gascoigne — Professor of Astronomy at the Australian National University — formally donated to the National Gallery of Australia his wife's last major work of art.

A series of 10 panels of sawn builders' form boards — the installation, Earth 1999, is valued at $2 million.

Gallery director Ron Radford confessed yesterday that he had not quite known what to make of the work when he first saw it. But now, on the walls of the national gallery, "one can clearly see it is one of her masterpieces", he said.

"The subtleties and richness of the tones, from deep reds and ochres through to browns and black across the installation evoke a feeling for the landscape — for paddocks seen from above and the ground underfoot."

It was completed in 1999, the year of Ms Gascoigne's death, but it had been a long time evolving.

The artist wrote to her son Toss in 1987 of her delight at discovering a stash of new material at a building site.

"My dining room floor is covered with builders' form board in various shades of brown, dull purple, and tan," she wrote. "I made a killing at a new building site opposite National Library. Stepped daintily down to the manager's office in my Carla Zampatti linen and my social shoes and asked if I might have any spare bits … I returned next day in my old pants and took a LOT … Plenty to go on with anyway! I wonder that no other artist is using it. I keep scrubbing concrete off it and laying it all over the floor until such time as it tells me what it wants to become."

Her son Martin recalled that the boards sat around the Canberra home for years, Rosalie watching the light play on their surfaces, shining in the rain and drying in the sun. She liked the colours and the humble nature of the material.

And then, quite suddenly, she began cutting it into rectangles and assembling it into panels, and sent her husband the astronomer off to the hardware store for aluminium mounting.

And now, thanks to the family's generosity, it is part of a renaissance at the National Gallery of Australia, which is celebrating its 25th anniversary with a $93 million building program to create a new entrance and extra exhibition spaces.