Restoring Emperor Qianlong's long-sealed-off lodge Juanqinzhai required an epic journey throughout the country. The Palace Museum had to find the last practitioners of the virtually vanished techniques used to fashion the building about two centuries ago.

Bamboo craftsman He Fuli recalls feeling anxious when called upon to help.

"The work was all about decoding ancient secrets to fix the damaged relics," the 69-year-old explains.

"Upon entering Juanqinzhai, I felt more like an archaeologist than a craftsman."

And He says that feeling never left him during his three years working on the site.

Wang Shiwei, deputy director of the Historical Architecture Department of the Palace Museum, explains: "Many of the techniques used at Juanqinzhai were lost. We had to do a lot of research to see if we could rediscover them to restore the building."

That's part of the reason the restoration lasted six years.

One of the greatest challenges was fixing the worn bamboo carvings. Experts headed to Zhejiang province's Dongyang, where bamboo craftsmanship has thrived for centuries, to seek someone up to the task.

After two failed journeys, they placed a newspaper advertisement as a last resort.

He's son-in-law spotted the advertisement, brought it to He, and he called.

While He and his team earned full marks on the exam, it took four months before the conservators responded.

He became the fourth generation in his family to craft bamboo, at age 15. But he had little inkling of the challenges he would face when he joined the restoration in 2004.

Qianlong loved southern China's bamboo thread marquetry and inner-skin bamboo carvings, so they were used extensively in his lodge.

Carving the bamboo inner skin requires several steps, including softening, smoothing and polishing before the skin is etched and the pieces glued on furniture.

Marquetry requires slicing and weaving bamboo strips into geometric patterns sometimes inlaid with jade. But Juanqinzhai's pieces were badly damaged over centuries of neglect.

While He had long practiced these otherwise mostly dead art forms, his work had long aimed at the commercial market and, consequently, worked with styles far removed from those used for the emperor's lodge centuries ago.

"I'd forgotten or had never learned many of the necessary skills," He says.

His task was massive.

All of the bamboo filaments in the theater's stage had fallen out.

He also had to work around such challenges as the prohibition of fire in the Forbidden City. His solution was to boil pigment-coated strips with an electric kettle, rather than roasting them on an open flame.

He also pored over ancient documents to rediscover a long-lost recipe for paste that can resist Beijing's dryness better than modern glues.

Some innovations came by luck. He was fortunate to find bamboo's usually discarded fibrous middle layer is perfect for etching detailed deer, birds and trees.

He says the lessons he learned during the three years he restored all of the lodge's bamboo objects have lasted beyond the project.

"They'll guide my future explorations," he says.

"And they show how many cultural legacies survive at Juanqinzhai. They could inject new elements into our modern lives once rediscovered."

While the bamboo work was extensive, the most important relic in Juanqinzhai is its damaged panoramic series of fragile murals painted on silk and then mounted on mulberry paper.

The restoration team headed to Anhui province in 2004, where traditional papermaking has survived.

There, they found 50-year-old Yu Yifu, who is the last person in his village to make paper the ancient way. The craft is in danger of disappearing, since most other villagers have turned to more profitable quarry work.

Yu started making paper as a teenager. But mulberry paper-production methods were long lost, so he started experimenting to rediscover the art.

It wasn't until the ninth attempt, after a year of tests, that authorities were satisfied, he says.

He was invited to Beijing to see the final product.

"I'd never seen such an exquisite place," he says.

"It could only be found in the Forbidden City. Surely, my work was worthwhile."

His success in Beijing has also brought more business to his workshop at home, as many new customers come for his rare paper.

"Some just want to look at it, and I explain it's not suitable for writing," Yu says.

Juanqinzhai's brocades, used in the beds and chairs, were also tricky to replicate.

The task was given to Zhang Kaicheng, a seventh-generation inheritor of the craft, who runs a brocade factory in Jiangsu's provincial capital Nanjing. His ancestors designed brocades for China's emperors, including Qianlong.

Zhang's factory used looms based on Qing Dynasty (1644-1911) designs. It mastered three of the four designs by 2006, but the techniques to create the rare zhuanghua (a kind of jacquard brocade) velvet remained elusive.

The Palace Museum's researcher Yuan Hongqi, who's in charge of fabric restoration, says: "The method for making that kind of velvet had been lost for more than a century."

The texture and colors were huge challenges.

They also had to rely on photographs, because the surviving pieces are too precious and fragile to be taken out.

Zhang and his colleagues pored over history books but couldn't find any reference to the ancient craft.

His factory's chief technician, Dai Jian, spent nearly two years leading a team to design a loom to make the special velvet.

Dai invented a system to regulate the brocade's density that uses about 1,800 tiny handmade clay weights that dangle from strings to control the fabric's tension.

"Their experiments have made the techniques better than ever," Yuan says.

Zhang's factory finally produced zhuanghua velvets that equal Juanqinzhai's.

Yuan says she was excited to announce her team was finally able to recreate jincai velvet, which is a blend of zhuanghua velvet and two other brocades.

Acclaimed embroiderer Gu Wenxia, 82, and about 30 others in Jiangsu's Suzhou, from where Qianlong ordered his embroideries, replicated their ancestors' skills to recreate the lodge's works.

They spent a year finishing 23 double-sided embroidery hangings to replace the worn-out pieces. By 2008, 260 hand-embroidered double-sided screens created by another embroidery team had been installed in Juanqinzhai.

In all, more than 20 craftspeople from southern China spent five years to restore Qianlong's lodge to its former glory.

This led authorities to understand the value of nearly extinct forms of craftsmanship and led to plans to train more people in these arts.

As Zhang says: "The restoration not only gave us a deeper understanding of the techniques used in the past but also of their importance - and the need to protect them - for the future."

Han Bingbin contributed to the story.