Why did Goujian sword not rust for thousands of years? What was the advanced manufacturing technology at that time?

Fifty years ago, a rare and unusual sword was found in a tomb in China. Despite being well over 2,000 years old, the sword, known as the Goujian, did not have a single trace of rust.The blade drew blood when an archeologist tested his finger on its edge, seemingly unaffected by the passage of time.  Besides this strange quality, the craftsmanship was highly detailed for a sword made such a long time ago. The sword measures 22 inches in length and has beautiful repeating dark rhombi patterns on both sides of the blade. In addition, there are delicate embellishments of blue crystals and turquoise, as well as concentric circles designed around the handle. Exquisitely forged from copper and tin, the markings on the sword also remain in excellent condition.

Surprisingly, the bronze sword  has traversed more than 2,000 years of history, but there is no rust on its body. What is the reason why it has been stainless for thousands of years?

We put sword of Goujian under a 500-fold microscope and took thousands of microscopic photos. We can see a yellow part, which is the blade of the sword. We can also see the dense structure like a branch. This is called "dendrite". This is the cell of the sword, which is the "metallographic tissue" inside the metal. Through this metallographic structure called dendrite, we can speculate and study its casting technology  and alloy composition.

According to the observation, this sword contains about 80% - 83% copper, 16% - 17% tin, and a small amount of lead and iron. Copper is a kind of inert metal. It is not easy to rust under daily conditions. This is first reasons why the sword is stainless.

Then look at the external environment of the sword: the tomb is buried several meters underground, the coffins cover each other, and the coffins are filled with a fine white clay around the coffin chamber, which has good compactness. In addition, the upper part of the grave pit has been compacted and filled with earth, which makes the tomb chamber almost a closed space. So many sealing layers basically isolate the air exchange between the tomb chamber and the outside world. Modern scientific research shows that steel will not rust even in neutral or slightly acidic water under completely oxygen-insulated conditions. This is the second reason why the sword is stainless.

The groundwater level of the tomb is relatively high, and the air content in the tomb room is less after being immersed in groundwater for a long time. This is the third reason.

The successful casting of Goujian sword, embodied the crystallization of the labor cooperation of moulding, model making, roasting, casting and mechanical processing at that time, which included the wisdom and creativity of the ancient Chinese people.