Using pig blood for preservation and minerals for coloring? What are the scientific mysteries of the ancient buildings on the central axis?

On July 27, 2024, "Beijing Central Axis - a Masterpiece of China's Ideal Capital Order" was officially included in the World Heritage List, making Beijing Central Axis a "golden business card" representing this city and even Chinese civilization.

Flour, pig blood and tung oil are the secrets behind the long-lasting beauty of the Jingshan architectural complex. The Beijing swifts, which fly almost their entire lives, like to "land" at Yongdingmen. The beautiful architectural paintings on Duanmen use a lot of mineral pigments... Are there such scientific mysteries about the ancient buildings on the central axis?

Jingshan - Spring is forever

Jingshan, located at the commanding height of the central axis, was the imperial garden of the Ming and Qing dynasties. Its buildings have survived wind and sun, but they still stand tall, thanks to the wisdom of ancient craftsmen - the "one hemp and five ash" groundwork technique.

0 1 “Di jiang” was originally used on pillars

Although wooden structures are stable and resistant to earthquakes and compression, they are susceptible to erosion by insects and rain. In order to protect wooden components, before painting the building surface, the area between the wooden base and the oil film must be "ground". The ground is made of ash and hemp, and is drilled with raw tung oil. This process was formed around the Ming Dynasty.

0 2What are “one hemp and five ashes”?

The specific process of "one hemp and five ash" ground construction can be divided into 9 steps. The process flow is: wood base treatment → juice slurry → joint ash → ash → hemp → press hemp ash → medium ash → fine ash → drilling.

All five types of mortars are made of oil, blood and brick mortar in volume ratio.

Do you know what these five layers of ash are? This technique uses hemp silk, hemp thread, linen cloth and five layers of mortar (including flour, pig blood, tung oil, etc.) to effectively prevent cracks, moisture, penetration, insect pests and decay, ensuring that the Jingshan buildings remain new over time.

0 3 “One hemp and five grays” shines with the light of science

Hemp is a splicing material. When the direction of hemp fibers is perpendicular to the direction of wood grain, it can effectively prevent cracking.

Brick dust is the main filler of the floor covering. Its surface is composed of multiple particles and has many uneven pores. After the brick dust is crusted, it can make the floor covering have good oil permeability and corrosion resistance.

Pig blood is used in the ground as blood material. Blood material mixed with mortar can improve construction efficiency and improve the adhesion, workability, waterproofness, crack resistance, drying properties, etc. of the mortar. Tung oil is scientifically used in the ground in two forms: raw tung oil and oil-filled tung oil. Drilling raw tung oil prevents cracking and fills the gaps between brick particles, playing a role in moisture and seepage prevention. In addition, tung oil is toxic and can prevent the growth and reproduction of fungi and insects after penetrating into the wood.

Yongding Gate - Swift Yongding

Yongdingmen, as the symbol of the southern end of the central axis, is not only a witness to history, but also the home of Beijing swifts.

The Beijing Swift is the only wild migratory bird in the world named after "Beijing". They often build their nests on ancient buildings in Beijing. They are the bird spirits representing Beijing and are often called the footless bird that never lands.

The structure of the Beijing Swift's claws means that they cannot hold onto branches or build nests on trees, but they can climb on ancient buildings; the structure of their tails and wings means that they cannot take off from flat ground, so they must perch on tall buildings such as the Yongdingmen Tower.

Beijing's urban area is the main distribution and breeding ground for Beijing swifts, while there are relatively few in the suburban counties. Beijing swifts mainly inhabit the gaps between the beams of ancient buildings or antique buildings that are suitable for building nests. The Summer Palace, Lama Temple, Qianmen, Temple of Heaven, and Temple of the Emperors of All Dynasties are their important breeding grounds. The end of March every year is the time when swifts fly to Beijing, and in early August of the same year, they will all fly away from Beijing to spend the winter in the south.

Duanmen Gate - Beautiful Colorful Paintings

There are many beautiful architectural paintings on the Duanmen Gate. Do you know where these colorful colors come from?

These beautiful colors use a lot of mineral pigments, among which azurite is one of the most commonly used pigments for architectural paintings.

The use of azurite in China can be traced back to the pre-Qin period, and it is also one of the earliest mineral pigments identified by modern chemists.

In the early 20th century, Zhang Hongzhao, a geologist who had returned from studying in Japan, tested and analyzed the azurite sold on the market and obtained the molecular formula 2CuCO3Cu(OH)2, which is azurite.

Why does azurite appear beautiful blue? Where do first-grade blue and second-grade blue come from? Why do minerals appear in such colorful and beautiful colors?

On the 5th floor of Building 2, Beijing Science Center, at the "Science and Technology Axis - Science and Technology on the Central Axis of Beijing" exhibition, we can carefully observe the structure of azurite, as well as its associated malachite (malachite) and other mineral pigments, such as red cinnabar (vermilion), etc., and understand the production process of mineral pigments.

The "Science and Technology Axis" exhibition not only allows the audience to feel the philosophical wisdom of the unity of man and nature and appreciate the exquisiteness and brilliance of ancient architectural skills, but also allows them to witness the ingenious integration of various scientific knowledge and scientific and technological achievements. What are you waiting for? Come and take a look!

References:

Zhou Qian. Decoding the "one hemp and five gray" groundwork techniques of the ancient buildings in the Forbidden City[J]. Knowledge is power, 2023, (10): 46-47.