“I quickly discovered that there were a lot of theories and misinformation,” she says, “but no one had actually done the scholarly research to find out.”

The result is Mahjong: A Chinese Game and the Making of Modern American Culture, a reader-friendly but fully footnoted account that leaves no tile unturned.

Heinz gives even the most incidental details: the right time of the year to cut the bamboo to make the pieces, the conditions in the mahjong workshops of the 1920s, the different chemistry of the plastic pieces that gradually emerged to take their place, and the social mores of players in Jewish summer camps in the Catskills of the 1950s.

As with much else in Chinese history – exaggerated claims for the longevity of Chinese culture, the visibility of the Great Wall from space, a language too difficult for foreigners – claims that mahjong was the “game of the Mandarins”, played 2,500 years ago by Confucius, were the ideas of marketing men from the West.

Mahjong emerged around the 1880s, eventually catching the attention of some expatriate Americans based in Shanghai’s International Settlement.

They competed with each other to streamline the game, simplify and standardise the rules, introduce factory-like production methods to the making of the bone-and-bamboo pieces, produce self-consciously Chinese caskets for the sets, wrap it up in mysterious Oriental myths, and promote the results to a novelty-seeking 1920s American public, first in China and then the United States. They were the ones who first labelled mahjong the “national game of China”.

The image of the game they sold was far from one of illicit gambling dens, but rather of sophisticated allure. Mahjong sought to represent a largely imaginary ancient China, and to be something new and exciting, a part of the Jazz Age.

Fu Manchu imagery overran department store window displays, while inside, young, white women dressed in silks and with Chinese hairstyles demonstrated the game. Socialites held charity fundraisers with dancers dressed as mahjong pieces, and mahjong-tile motifs appeared on fabrics.

By 1923, mahjong exports to the US were worth US$23 million in today’s money. China was unable to provide enough cow shin bone to keep pace with demand, resulting in imports from America.

The game’s social impacts were many. The dubious history attached to mahjong joined chop suey, General Tso’s chicken and fortune cookies to form part of many Americans’ idea of China to this day.

Mahjong tutoring provided a new and well-paid source of employment for Chinese-Americans, even if some did no more than read one of the American-produced rule books and repeat the contents.

Heinz’s Kunming friend taught her a basic version of the Chinese game learned from her Shanghainese grandfather. Perhaps this was close to the original game, before its adaptation for export by promoters such as former Standard Oil representative Joseph Babcock.

There’s no guarantee. “Because we have a spotty evidence base for the game’s evolution in China, especially before the 1920s, we don’t have much detail of exactly what was the version he first learned, and what changed between that and what he presented to an American audience.”

Some evidence can be found in legal actions in which Babcock sought patents in order to maintain control, although he probably exaggerated the uniqueness of his version of a game that, as his opponents objected, was widely played in China.

“Lots of people who play the American version do not know that they’re actually playing a uniquely American version,” says Heinz. This has entirely different scoring rules, among other things.

She sees the game as a historical agent for assorted social changes on both sides of the Pacific, and in particular in its role as a social lubricant among marginalised and peripatetic minorities.

For Japanese-Americans interned during World War II, it provided a way of easing into the society of new camps after frequent transfers.

For American Jews, whose post-war upwards social mobility also led them to make more frequent moves, it provided an introduction to new communities that overcame differences of sect or origin. For air force wives, subject to the frequent shifts of their husband’s postings, it had the same effect.

“Not only is it a shared game or activity that allows you to connect and meet people,” says Heinz, “it has specific rhythms that make just the right amount of time to have a conversation between each round of play as you shuffle the tiles and build the wall.”

By the ’50s, the game had lost its exclusive social allure, and variants had emerged that increased the element of chance and reduced its reputation as a respectable intellectual challenge, rather than a mere gambling game.

Several women formed the predominantly Jewish National Mah Jongg League to revive the game and standardise a new set of rules based on their own preferences.

Here was the answer to Heinz’s aunt’s question, although American “mah-jongg”, with new “joker” tiles, may now be unrecognisable as mahjong, and vice versa.

A busy career means Heinz has no time to play these days, “but it’s just so pleasurable to hold the tiles, to look at them, to see this range of imagery”, she says.

The historian hopes to play again eventually, but whether it will be the Chinese or the American version she’s not sure.