In money terms, the NGA said its most valuable painting - Blue Poles by Jackson Pollock - was put at half a billion - $508,056,322 - by a company of valuers, JLL Public Sector Valuations.

The eye-watering sums are more than enough to solve the current lack of funds for public institutions in Canberra, and more than enough to pay for the Australian War Memorial expansion.

But one of the country's leading art historians has said it would be wrong to think of selling off paintings to pay for immediate needs.

"Selling Blue Poles to keep the building open would be nonsensical," according to Sasha Grishin, author of 30 books on art including Australian Art: A History.

He likens the idea to that of a bank selling off its monetary assets in order to keep the bank building itself open.

"The purpose of the National Gallery of Australia is the collection of national heritage treasures, of which Blue Poles is one of the highlights," Professor Grishin who is also the art critic of The Canberra Times said.

The NGA bought Blue Poles in 1973 for $1.3 million. The gallery's director at the time, James Mollison, had to seek approval from the prime minister Gough Whitlam because he wasn't authorised to go above a million dollars.

The "abstract expressionist" work was painted by the New York artist Jackson Pollock in the early 1950s. It is a swirl of colour on a large canvas not far off two metres by five metres.

The artist created it by dripping, splashing and pouring paint on the canvas as it lay flat on the floor. He used sticks and cooking basters. Sometimes, he just poured the paint out of the can.

Every so often someone suggests that it be sold off.

"It'll only be worth something to taxpayers when we sell it," the Liberal senator James Paterson suggested in 2016, when it was valued at "only" $350 million.

"My view is that it's not appropriate for the Federal Government to own a single piece of art worth $350 million, it would be one of the most expensive paintings in the world."

His office did not respond to a request for comment after the latest valuation.

The National Gallery of Australia said that the work had appreciated in value by $506.7 million since its acquisition for $1.3 million.

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"Jackson Pollock's Blue Poles is by far the most valuable artwork in the National Collection because it's one of the most important works of the 20th Century," an NGA spokesperson said.

"It's an exemplary painting of the abstract expressionism movement and was the final instalment in a series of works by Pollock which changed the course of modern art."

Art critic Sasha Grishin said he felt a "tingle" when he looked at the work.

He praised the NGA director of the time, James Mollison: "We are very fortunate that we had a director of genius. Jim was magnificent because he bought what was internationally significant."

To those of the "a child could do that" school of art viewers, Professor Grishin says of Blue Poles: "It grows on you in time."

But he does relate how he was standing in front of it once and a woman next to him said: "Two inches of that would buy me a washing machine."

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