The oldest cast iron structure in the world - the Cangzhou Lion
For the past 100 years Western historians have until fairly recently looked for links for the passage of iron technology from Europe to China. Aside from being a little arrogant in assuming it had to flow from West to East there are indications that iron technology developed independently until the point there was a technological convergence through trade. Even then China continued with practices and techniques that were centuries old. Ironworking has always assumed to have been developed around Greece - Egypt and Mesopatamia.
The work of Western academics like Donald Wagner (see http://donwagner.dk/index.html )and early on from Thomas Read in the early 20th Century has identified remarkable and often unique ironworking traditions, and manufactures which even today are remarkable, including the oldest iron structure and sculpture in the world.
In Western terms the technological evolution of iron production followed a fairly systematic process. Meteoric iron and a very limited amount of natural ‘telluric’ iron from Greenland was worked along with natural bog iron until iron ore was processed in small furnaces and wrought iron was produced. Cast iron was not introduced to Europe until the 14th Century. This line of development was also the same for most other locations, but not China.
In China, cast iron was much more commonly used and developed in use prior to wrought iron (“shu tie”)and later steels. The thinking for this is that copper smelting in China on a vast scale for casting bronze produced cast iron as a bi - product. As the raw materials for making bronze became more scarce and the demand grew, the Chinese started to use cast iron instead, whose ore was much more readily available. Higher temperatures were required, but this was found to be reducible by the presence of other elements such as phosphorus.
Cast iron objects have been found in China pre-dating the 5th Century BC. In this period Chinese ironworkers were employing blast furnace technology not seen in Europe until the medieval period. Donald Wagner suggests that by the 11th Century the iron industry in China was by some measure “the world’s largest and most technically advanced, and had been so for at least twelve centuries”.
Cast iron Buddha statues and oxen were made in the 7th - 8th Century, and cast iron coins used in the Song Dynasty of the 9th Century. Cast iron was used for many centuries for implements and tools for the most part but it was also used for something much more unusual, in the manufacture of remarkable cast iron sculptures of considerable scale. A Japanese Buddhist monk called Ennin recorded large cast iron statues and pagodas during 838 - 847 as he travelled across China. A purge against Buddhism over the next decade destroyed most of the evidence of these iron structures.
The 17.9m Yuquan cast iron temple of 1061 is a notable survivor of this prowess in casting, it’s weight of 38,300 kilograms recorded on the structure.
The largest, oldest and most remarkable cast iron structure in the world is the cast iron lion of Cangzhou cast in 953. It is 5.78 m (19 ft) high, 6.5 m (21 ft 4 in) long, 3.17 m (10 ft 5 in) wide, and has an estimated weight of 40 tonnes (44 tons). This remarkable structure was thought to have been located within in the Kaiyuan Temple in Cangzhou. After taking the throne in 713, Emperor Xuanzong issued the decree building "Kaiyuan Temples" which was named after his reign title "Kaiyuan" The cast iron lion carried a bronze statue of the bodhisattva Manjusri on the lotus seat which has been lost.
By 1603, its tail was lost. In 1803, a storm toppled the statue resulting in damage to its snout. In 1886, it was supported with stones and bricks on the orders of a local magistrate. Because of its position it seemed to be regularly flooded which is also evidenced bbq the external corrosion to the feet. In 1961, it was listed as a national key cultural relic and a canopy erected. In 1984, the iron lion was remounted on a stone pedestal. Its legs were filled with cementitious material which prompted cracks to appear in the sculpture. Restoration work was carried out in 2000 which saw the addition of further material to ‘protect’ the iron and a steel framework introduced to support the structure.
Aside from the scale and ambition of the casting and its early date, a highly unusual feature of the casting is that it is not cast in individual components, but rather made using a piece moulding technique in one mould. This technique has been used for casting bronze objects for many centuries so it is technologically logical that this approach was used.
There are two ways the statue could have been made.
In the first, a clay model of the sculpture was made and allowed to dry. This model incorporated all the raised detail of the final casting. It was then covered with a new layer of clay after drying which took on the impression of the detail beneath. This outer layer of clay was then cut into pieces and removed before it dried completely. The detail of the impression made could be further modelled to improve the casting detail. Next, material is taken off the surface of the inner clay model in order to create a void for pouring the iron between the outer and inner mould. Iron bars called chaplets would support the two clay walls and be incorporated into the casting - a common method of casting hollow objects in later periods.
In the second approach a clay model of the sculpture was made and allowed to dry. This model did not incorporate all the raised detail of the final casting. It was then covered with a new layer of clay after drying which had the final detailing worked into the clay interior face. This outer layer of clay was then cut into pieces and removed before it dried completely. The detail of the impression made could be further modelled to improve the casting detail. Next, material is taken off the surface of the inner clay model in order to create a void for pouring the iron between the outer and inner mould. Iron bars called chaplets would support the two clay walls and be incorporated into the casting - a common method of casting hollow objects in later periods.
Because melting that much iron to cast in one go would have been difficult to manage, the casting was done in sections or panels. There remains a great deal of evidence of its manufacture including chaplets and pins cast into the structure.
I was fortunate to visit the Lion in April 2019 and was given permission to access the statue with local officials. It has sadly continued to deteriorate due to exposure and some of the previous interventions. I hopefully can help support renewed efforts to conserve this astonishing piece of work of global significance.