Zhou Qunfei is the world’s richest self-made woman. Ms. Zhou, the founder of Lens Technology, owns a $27 million estate in Hong Kong. She jets off to Silicon Valley and Seoul, South Korea, to court executives at Apple and Samsung, her two biggest customers. She has played host to President Xi Jinping of China, when he visited her company’s headquarters.

But she seems most at home pacing the floor of her state-of-the-art factory, tinkering.

She’ll dip her hands into a tray of water, to determine whether the temperature is just right. She can explain the intricacies of heating glass in a potassium ion bath. When she passes a grinding machine, she is apt to ask technicians to step aside so she can take their place for a while.

Ms. Zhou knows the drill. For years, she labored in a factory, the best job she could get having grown up in an impoverished village in central China.

“She’ll sometimes sit down and work as an operator to see if there’s anything wrong with the process,” said James Zhao, a general manager at Lens Technology. “That will put me in a very awkward position. If there’s a problem, she’d say, ‘Why didn’t you see that?’ ”