It’s the British Museum’s latest treasure; it cost nearly half a million pounds and it records a defining moment in the history of Japan, when two centuries of isolation came to an end and Japan agreed to trade with the west. It’s the Perry Scroll and it’s on display now, showing a different section each month between April and October.

In July 1853, US Commodore Matthew Perry’s four warships, the famous ‘Black Ships’ steamed into Edo Bay to deliver a letter from President Fillmore requesting trade relations with Japan. After that initial contact, Perry came back the next year with a fleet of nine ships and on 31 March 1854 the Treaty of Kanagawa was signed. It was Japan’s momentous first step out of its feudal past.

The Perry Scroll depicts the second visit of 1854, though it was probably produced in 1858 to commemorate the second Kanagawa Treaty. It’s beautifully drawn and was probably done by Hibata Ōsuke, as it’s based on the sketches he did at the time. He was one of two artist-retainers who were present at the negotiations, one disguised as a physician to a magistrate who was one of the main negotiators, the other as his medicine-box carrier.

What makes the scroll so fascinating is that it’s not an official record, so it can afford to show some of the more interesting behind-the-scene moments. It starts off quite soberly with the ships sailing into the bay.

The Americans landing at Yokohama in twenty-seven barges.

A banquet for the American negotiators (facing you) and their Japanese counterparts (with their backs to you).

But then we get lighthearted scenes that suggest the two sides got on extremely well and after a hard day of negotiating everybody let their hair down.

The Japanese laid on a sumo wrestling match, and the scroll shows us the Americans meeting the wrestlers afterwards and prodding their muscles in disbelief.

Presumably in return, the Americans invited their Japanese hosts on board their ship, the Powhatan, to see a minstrel show by troupe of sailors called the ‘Ethiopians’. (In blackface! What on earth did they use to black up?)

The Americans seem to have come prepared for a good time – they brought a brass band with them, whose instruments fascinated the Japanese.

And they gave the Shogun a quarter-size steam engine, carriage and track – what a brilliant present! I wonder where it is now?

There were some sadder moments too – like the funeral of a cabin boy who died at sea before reaching Japan.

So who did the scroll belong to originally? The preface by the poet Onuma Chinzan says ‘Mr Maruyama had an artist paint this’, but we know little of the mysterious Mr Maruyama, nor how his scroll came to be in the hands of the dealer in antiquities from whom the British Museum bought it.

Wherever it’s been, it’s still in great condition. The paintings, on silk-backed paper, are as clear as the day they were painted and the only worm damage is to the unpainted margins.

The scroll is on display until October in the Japanese Gallery (Room 92) at the British Museum. At the moment they’re showing the picture of the little train and the musical instruments. Scenes not currently on display are illustrated along the bottom of the display case, but I wish I’d gone last month as well and caught the minstrel show before it disappeared.