A large Jingdezhen porcelain Mao button. Jingdezhen is a city in Jiangsu province famous for high-quality porcelain. Porcelain has been produced there as early as the sixth century CE. It was once the manufacturing area of porcelain for the Emperors.
The back view of the button shows a an imprint of the characters 著毛主席高寿无疆, “Wishing Chairman Mao Longevity With No End.”