The floor is entirely covered with a deep layer of what appear to be grey pebbles. It is like a bleak Suffolk beach, and a toddler, getting into the spirit of it, has shed her shoes and is having a sit-down in her stockinged feet. Adults are not so comfortable: as if caught out by a freak snowstorm in the wrong shoes, several are picking a distinctly wobbly way over the crunchy, uneven surface, suddenly looking out of place in autumnal London clothes.
This is the latest installation in Tate Modern's Turbine Hall – a series of wow-factor installations that have, over the past decade, included Doris Salcedo's Shibboleth, a deep fissure running through the concrete floor of the building, and Olafur Eliasson's The Weather Project, which filled the space with mist and mirrors.
There is more to Chinese artist Ai Weiwei's installation than meets the eye, however. Bend and pick up one of the "pebbles" and you can see that it resembles a sunflower seed encased in its striped husk. In fact, each one – and there are 100 million of them, covering an area of 1,000 square metres – is handmade from porcelain and has been individually handpainted.
Ai – a bearded, impassive, black-clad figure, who snapped the photographers surrounding him at today's press view almost as busily as they did him, and posted the results on Twitter – had the "seeds" made in the southern Chinese city of Jingdezhen.
"Historically, the town's only activity has been making porcelainware for over 1,000 years. The super-high-quality skill for generations has been making imperial porcelainware," he said. "In modern days, however, it has become very commercialised."
Harnessing traditional craft skills, each seed was moulded, fired, and painted with three or four individual brush strokes, often by women taking the objects home to work on them. One thousand six hundred people were involved in the process. "Even taxi drivers were talking about it," he said.
"I tried to explain to [the artisans] what we wanted them for, but they found it very difficult to understand," said Ai. "Everything they usually make is practical, and the painters are used to creating classically beautiful flowers using a high degree of skill."
He said that the workers had been paid a living wage – in fact slightly more than customary – to work on the project. "Now they are asking when we can start again," he said. "I shall have to think of a new project."
Sunflower seeds, he said, had a particular significance in recent Chinese culture and history. During the cultural revolution, Mao Zedong was often likened to the sun and the people to sunflowers, gazing adoringly at his face. But sunflowers were also a humble but valued source of food in straitened times, a snack to be consumed with friends.
Ai also likened the artwork to Twitter – a vast sea of ideas and communication contributed by individual people. Ai now uses Twitter regularly after the blogs he kept were in turn censored by the Chinese authorities. One of his online projects has been to amass the names of those killed in the Sichuan earthquakes of 2008.
What if the temptation to put one of these lovingly made objects in your pocket becomes too great? Smiling, he said: "They might also want to eat one, and that would be a safety issue for the museum." He added: "If I was in the audience I would definitely want to take a seed. But for the museum, it is a total work, and taking a seed would affect the work. Institutions have their own policies. But I know I would want to take a seed."
A spokeswoman for the museum confirmed that they would be "encouraging people not to" depart with a souvenir. After the installation at Tate Modern is closed (it is on show from tomorrow until 2 May) the seeds, which weigh 150 tons, will be shipped back to Ai's studio in Beijing, where he will think about using them for another project.
Did he make any of the 100 million sunflower seeds himself? "I made three or four," he said. "But none of them was any good."
