How do you digitize a 17th-century book that’s always been considered too fragile to open?

Very, very carefully.

Technically known as Shi zhu zhai shu hua pu, it is more commonly known as the Manual of Calligraphy and Painting. It is also considered to be the earliest Chinese book printed by the technique of polychrome xylography. The technique, also known as douban, was invented and perfected by Hu Zhengyan in the 17th century, according to the Cambridge University Library, which owns the book.

“The method involves the use of multiple printing blocks which successively apply different colored inks to the paper to reproduce the effect of watercolor painting,” explains the library. “Great skill is required to achieve a convincing result, but the beautiful gradations of color in this work have led to its reputation as ‘perhaps the most beautiful set of prints ever made.’”

“The seventeenth century was a period of conspicuous consumption in China, and books like this were luxury objects created for pleasure rather than learning,” explains the British Museum. “Great attention was paid to the creation of each illustration. Care was taken so that the subtle tonalities of color and fine brushwork of Chinese painting could be reproduced in the medium of print.”

The book includes 140 illustrations, divided into eight categories: birds, plums, orchids, bamboos, fruit, stones, ink drawings (round fans) and miscellany. This particular copy of the book is thought to have been made in 1633 by the Ten Bamboo Studio in Nanjing, and is estimated to be worth millions.

And nobody had ever seen it.

“The binding is so fragile, and the manual so delicate, that until it was digitized, we have never been able to let anyone look through it or study it—despite its undoubted importance to scholars,” writes Charles Aylmer, head of the Chinese department at Cambridge University Library.

“The book is printed and bound in a special way call a butterfly binding,” says Grant Young, head of digital content for the digital content unit of the Cambridge University Library. “The leaves are printed on one side only, folded in half and glued together along the outer fold,” explains the library. “This copy has been identified by the leading scholar of this work as the finest and only extant complete copy in the original binding of what he describes as the ‘second superstate’ of the first edition.”

In fact, it was the binding that was part of what makes this work so special, Young says. “One of the special things about this copy of the book was that it retained its original nearly 400-year-old binding and covers.” Although it had been reprinted many times, complete sets of early editions in the original binding are extremely rare, Aylmer writes.

But that’s been the challenge in seeing the book to-date: Fear of damaging the binding. “It’s not that the book was impossible to open,” Young says. “As you can observe, we have been able to open it to photograph it. It’s just that we had not let people open it previously because of the risk of damaging it.”

This is where the “very, very carefully” comes in. Rather than using a scanner, the book was digitized, with assistance from the curator and conservators, by photographing the pages with professional, high-resolution (80 megapixel) cameras, Young says.

The result is that, for the first time, people all over the world can see the exquisite images. “Each image is followed by a text or poem, interspersed with instructions for basic artist technique, like the correct way to hold a paintbrush,” writes Meg Miller in Co. Design. “For the 200-plus years it stayed in print, the book had a huge influence on color printing all across China.”

The book is just one of the items from the library’s Chinese collection that have recently been digitized. Other recently digitized items from the Chinese collection include:

One of the world’s earliest printed books, a Buddhist text dated between 1127 and 1175

‘The Manual of Famine Relief,’ a 19th-century manuscript with instructions for the distribution of emergency rations to famine victims, including practical advice about foraging for natural substitutes to normal foodstuffs in the event of an emergency

A 14th-century banknote, printed on mulberry paper, long before it was used in Europe—and threatening decapitation to forgers

Three oracle bones(ox shoulder blades and turtle shells), which record information on a wide range of matters including warfare, agriculture, hunting and medical problems, as well as genealogical, meteorological and astronomical data, and are the earliest surviving examples of Chinese writing in the world

It’s the Manual of Calligraphy, though, that’s really captured people’s attention, due to the exquisite illustrations. Digitizing it has enabled us to open not just the book, but a window to another time.