Terracotta warriors in Pit 1 [Photo by Fan Zhen/chinadaily.com.cn]

"The rare relics including the Qin terracotta warriors were collected from museums throughout Shaanxi province and packed in more than 10 large wood boxes," Pang said.

Staff from the three institutions carefully checked and transferred each piece, including a set of a stone armor, a class-one heritage with national protection unearthed from near the Mausoleum of Emperor Qin Shihuang in Lintong district, an eastern suburb of Xi'an.

In order to check each piece of the armor, the Chinese and US experts divided its 617 stone pieces into nine areas — each shoulder, the chest, back, upper body, both ribcages, the breast and lower back — and then inspected every part.

"We checked if any piece of the armor had stains or was incomplete and recorded it," said Zhang Zheng, a program manager with the center.

Zhang said it took more than five hours to complete the inspection of the armor and it was hard work.

They similarly inspected every item and recorded everything in minute detail. The records were then translated into both Chinese and English versions and signed by those involved.

"Although that suit of armor had been exhibited many times overseas, we could not use the previous records for the next exhibition but have to check the relics again and again before every exhibition, as we must not make any mistakes with these very much precious relics," Zhang said.

In addition to the written records, more than 200 photographs were taken of the relics.