There is so much more to the real-life Bligh than his part in the mutiny aboard the Bounty. And yet, because Hollywood has made so many versions of that calamity with so many great actors (including Trevor Howard, Marlon Brando and the best of them all, Charles Laughton) portraying Bligh so memorably, it is hard not to go looking for hints of them in the smooth, youthful face of the Webber portrait.

In the 1935 movie version (voted that year's best picture) Laughton's Bligh is a callous monster (his heartlessness towards his crew reminiscent of the Abbott government's attitude to asylum seekers) and so we looked closely at the Webber Bligh in search of traces in the face of the monster to come. We wondered if the gallery's director Angus Trumble (on Tuesday a picture himself in a bow tie of unusual flair and splendour) could see any such traces.

"I'm not sure," Trumble mused, while saying that it is one of the joys of the painting that we know when we look at it we are looking at a young man in whom later turbulence is brewing.

"The Charles Laughton [Bligh's tyrannical side] is coming. He's in there [within the young Bligh], implanted. Bligh was hot-tempered. All his life he had what today we'd call anger-management issues."

To us and to the audience there for the portrait's introduction to the nation Trumble reflected that "As a portrait it's fairly conventional. It's the kind of portrait produced in large numbers, usually for officers departing on long voyages".

"But of course for us [for the gallery and for Australia] the interest is in Bligh himself. He was a complex and fascinating man. He was one of the most remarkable navigators of the 18th century. And he would be famous alone just for the epic journey [of 6700km] that he undertook after the mutiny on the Bounty, navigating solely by the stars, to Timor.

"But of course he is of national significance to us because, having gone through the misfortune of Bounty, he faced insurrection during his term as fourth governor of New South Wales. There has ever since been in Australian history a bellwether William Bligh. There's been Bligh as tyrant and Bligh as martinet, versus Bligh the man of science, the lonely husband and father, the officer of the Royal Navy whose tenure and service was again and again endorsed by the lordships of the Admiralty in London. He's a flash point for the writing of Australian history. So this picture takes its place among the most important early works to document the history of this country.

"And this William Bligh [gesturing at the young master mariner, about 25, in the richly gilded frame] is none of the ones I've just mentioned. This is the young man of promise, a young man who at this point [already skilled in navigation and seamanship] was selected, hand-picked by James Cook, to sail on the Resolution on that epic voyage. So this painting is wonderful. It's just perfect for us."

Trumble hinted that the painting, purchased by the gallery through Christie's in London, had been eye-wateringly expensive (we were not vulgar enough to ask how many shekels had been spent) and that it was only the philanthropy of the Liangis family that had made this exquisite shopping expedition possible.

The new painting has been hung in exalted company. It shares a wall with another John Webber work, Portrait of Captain James Cook RN, 1782 and Thomas Phillips' Portrait of Sir Joseph Banks, 1814.

If, at night, the people in portraits in a portrait gallery come alive and walk about and talk to one another (and of course they do) then what wonderful yarns these three, and their neighbours (who include Trucaninny of Van Diemen's Land in Benjamin Law's 1836 bust of her) must share.

There is something eerie about paintings of quality. However often you visit them and ogle them there seems to be something new going on in them. At our first ogle at the portrait on Tuesday morning (having a quick look for the face's Laughton, Brando and Howard sides) there was, we swear, only one ship on the water behind the young mariner. But by the time, a little later, we were standing beside the painting with director Trumble, the white sails of two more vessels had come up over the curve of the earth and were there on the horizon. We pointed this out to one gallery employee, and she too had never noticed those ships before.

The portrait is, for an artefact perhaps 240 years old, in wonderful condition. Its short history known to Angus Trumble is that it stayed in the embrace of the Bligh family for a long time and then somehow passed to the family's executor and then to his family. In the 1860s it was offered to the National Portrait Gallery in London but it declined to buy it, probably because Trumble thinks, the young gallery was then "in the statesmen and sovereigns business" so that Bligh was not thought grand enough.

"Things would be very different now," Rumble is sure, proud and glad of the acquisition of a work just perfect for his gallery and for the nation.