"Once it started, it felt like eating peanuts out of a bag - you want to search for more."
He bought a drawing every two to three years, sometimes donating to the small collection of the National Gallery of Art in Washington.
Stone first came to China in 1982, to teach as a visiting scholar at Beijing's Capital Normal University. He returned regularly, lecturing at universities and academic institutions nationwide.
"In America every major university has an art museum. Princeton has a permanent collection of works of masters such as Van Gogh, Monet and Renoir. It is free. Students can just come over to see these beautiful pieces and then go back to their studies," Stone says.
In China, he laments, "it is not common".
Stone's collection not only delights the students at PKU. It has toured Macao and Urumqi, the Xinjiang Uygur autonomous region, where hundreds of people lined up in snow to see their first Picasso work.
Stone's generosity has sometimes yielded surprises.
