"It was a medium that transformed abstract concepts, including numbers and drawings, into something tangible that the decision-maker could clearly understand," he adds.

One of the most delightful details in the exhibition involves those yellow slips — the very same ones Xi described in his dissertation.

On the replica created by the Berlin students, the yellow slips were covered by their handwriting.

"To be honest, their Chinese is probably at a beginner level. But in those somewhat naive brushstrokes, you can actually see their genuine interest in tangyang and in traditional Chinese craftsmanship," Lin says.

The collaboration also revealed how differently Chinese and German students approached the same object.

Tsinghua University students tend to see tangyang as a cultural relic, while in the eyes of the Berlin students, it is an architectural model, he adds.

Wen Wen, another co-curator of the exhibition and a graduate of Tsinghua University's School of Architecture, says tangyang is a relatively niche field, both in China and Germany.

"So for most students, it was something new and interesting. They were genuinely curious," she notes.

The German side had the original tangyang models, but they lacked the capacity for in-depth research.

"Before we got involved, they had done basic documentation, but no deeper research. After Xi Fuquan, very little had been done," Wen points out.

Tsinghua University, on the other hand, had been systematically documenting and analyzing its own tangyang collection since 2019.

"We used a range of scientific methods, and took X-rays to see the internal support structures. We used microscopic cross-section analysis and polarized light microscopy to analyze pigments, paper types, adhesives, and craftsmanship," Wen says.

These techniques were applied to the Berlin museum's tangyang models, with some limitations, because the models couldn't be moved.

Still, the collaboration opened new doors.