Ordinarily, when oxygen is allowed to circulate freely inside a kiln, the iron in the clay stays in its oxidized red form. To make blue bricks, water is poured into the kiln near the end of the firing process, generating steam. This inhibits the circulation of oxygen, leading to incomplete combustion. To compensate, oxygen atoms are pulled out of the iron compounds in the clay, changing it from red iron oxide (Fe2O3) to black iron oxides (Fe3O4 or FeO). This chemical reaction is called reduction.

It is not clear why this practice was adopted, but blue bricks have been found in China’s archaeological record as early as the Qin Dynasty (~200 BCE). It is possible that reduction helped to create a denser, stronger and less porous brick. Black iron oxides act as a flux lowering the clay’s melting point, allowing it to sinter (shrink and densify) and vitrify (turn to glass) at a lower temperature than would otherwise be required. Modern factories generally fire bricks at between 1,000°C and 1,200°C, but lab tests show that old blue bricks were fired at between 600°C and 1,000°C. 

However, China also had cultural reasons to favour blue bricks, perhaps associating the colour blue with cool and dark yin energy to balance out hot and dry yang energy that represented the ever-present risk of fire in towns and villages. The major exception was the Minnan region of southern Fujian and Taiwan, which developed a distinctive tradition of red brick architecture. 

What about Minnan and Taiwan?

No-one is entirely sure why Minnan and Taiwan are different; there are several theories, none of which are fully satisfying. One theory goes that the Min people were sailors who built brightly coloured houses that could be easily spotted while at sea.

Another theory is that Minnan absorbed foreign influences due to its long and extensive role in maritime trade. Quanzhou was a wealthy port between the 11th and 14th Centuries, with links to Southeast Asia, India, Africa and the Middle East. From the 16th to the 19th Centuries, Zhangzhou imported Spanish silver via Manila, in exchange for tea, ceramics, and silk. In the 1840s, Fuzhou and Xiamen were ceded as European treaty ports under the unequal treaty signed following the Opium War.  

Many have suggested that Minnan was specifically influenced by Spanish colonial architecture in the Philippines or Dutch forts in Taiwan, but archaeological evidence of the use of red brick in Minnan predates European imperalism in Asia, going back to at least the Southern Song Dynasty (12th to 13th Centuries). It is unclear how common red brick buildings were back then, so it is possible that Spanish and Dutch influences later popularized the style, which peaked in the Qing Dynasty (17th to early 20th Centuries). 

A third theory is that Fujian’s overseas Chinese merchants built red houses to show off their wealth in defiance of sumptuary laws, which restricted the use of red walls to the imperial household. However, since Fujian was so remote, the laws were not enforced. One of the largest and best-preserved red brick compounds in Quanzhou was built in the late 19th Century by a clan of Chinese-Filipino merchants, the Cai family. 

At best, these theories address why the people might have favoured red buildings, but not why their brickmaking methods differed. In any case, Fujian’s mountainous terrain isolated it from inland China and likely contributed to the development of a unique seafaring culture with its own distinctive architecture. The style was then brought to Taiwan by Fujianese migrants during the Qing Dynasty. 

Red vs. Blue

During the mid-19th to mid-20th Century, blue bricks were gradually supplanted by red bricks in major cities such as Shanghai and Hong Kong due to western influences and the introduction of modern industrial technologies. The Europeans who established themselves in mainland China and Hong Kong thought that blue bricks were of unsatisfactory quality and tried to source European-style red bricks. At first, they were imported from Europe as ballast (extra weight placed in ships for stability), but soon started to be made locally by traditional brickyards.  

In Hong Kong, red bricks were imported from the UK, and from kilns in Foshan (“Canton bricks”), Taiwan (“Formosa bricks”), and Xiamen (“Amoy bricks”). Of the three, Amoy bricks were thought to be the most durable, and were therefore used as facing bricks on external walls. Western Market (built 1906) and the University of Hong Kong Main Building (built 1910-12) are two examples. 

Hong Kong’s colonial government thought that blue bricks were of such poor quality that they actually restricted their use. The Buildings Ordinance of 1889 banned the use of blue bricks in buildings over 36 feet (11m) tall, and by 1903, they could only be used on the top floor of buildings where they would not bear much load.

But where did this belief come from? It probably came from a mixture of cultural arrogance and limited experience. As early as the 18th Century, European diplomats who visited China regarded local blue bricks dubiously, calling them “ill-burnt” or “half-burnt”. Red bricks are not automatically tougher than blue bricks; both vary widely in quality. If you have ever picked up a modern red brick from a construction site, you may have noticed that some are so soft that bits easily chip off, while others, such as the ones used to pave roads, are extremely hard and dense. 

The highest quality blue bricks (called “golden bricks”) which were made specially for use in the Forbidden City, are stronger and denser than stone. However, most of the blue bricks encountered by Europeans in Hong Kong and treaty ports were likely of low quality. Pre-colonial Hong Kong was a remote settlement that did not have access to the best brickmaking techniques. Most bricks were made locally by unskilled villagers in temporary kilns. The bricks of some ancestral halls in the New Territories exhibit a reddish or brownish blotchiness, a sign of incomplete reduction. The fact that they were used anyway indicates that local builders were unable to obtain better materials. 

Moreover, during the second half of the 19th Century, a lot of tong lau were built as quickly and cheaply as possible. It is not hard to imagine that corners were cut to supply Hong Kong’s urban expansion with large volumes of inexpensive building materials. Construction standards were generally poor and building collapses were frequent, giving blue bricks a bad reputation. There was a similar situation in cities like Shanghai, where a large number of siheyuan (courtyard houses) were hastily constructed to accommodate a massive influx of people seeking safety in European-controlled areas from the Taiping Rebellion.

Making high quality blue bricks in the traditional way was a time-consuming, labour-intensive process that could only be done in small batches. Though low tech, it required experienced craftspeople knowledgeable about the characteristics of local clays and how to precisely control the temperature and timing of the firing. 

By around the 1920s in major cities, traditional brickyards were outcompeted by modern factories, which could produce a standardized and consistent product more quickly and cheaply. But by the 1930s, both blue and red bricks started to be displaced by a new building material—reinforced concrete. Now, bricks are mostly relegated to internal partition walls, where they no longer need to be load-bearing and are covered up with plaster. Now that brick quality matters much less, conservationists and materials scientists are studying traditional bricks to ensure that brick buildings can be properly conserved before all of the older knowledge and techniques are lost. 

Sources

Special thanks to Dr. Shu Changxue, Assistant Professor at the University of Hong Kong Faculty of Architecture for sharing her knowledge and insights. 

Changxue Shu et al., “China’s brick history and conservation: laboratory results of Shanghai samples from 19th to 20th century”, Construction and Building Materials, v. 151, 2017, pp. 789–800. 

Changxue Shu, “From the blue to the red: changing technology in the brick industry of modern Shanghai”, The Proceedings of the Fifth International Congress on Construction History, vol.3, pp.313-20, USA: Lulu and The Construction History Society of America, 2015. 

Changxue Shu and Thomas Coomans, “Towards Modern Ceramics in China: Engineering Sources and the Manufacture Céramique de Shanghai”, Technology and Culture, v. 61, no. 2, April 2020, pp. 437-479.

Ivan Chi-ching Ho, “The study of the Chinese (grey) brickwork in the vernacular buildings in Hong Kong”, MSc thesis, University of Hong Kong, 2002. 

Peng Zhao, “Conservation of disappearing traditional manufacturing process for Chinese grey brick: Field survey and laboratory study”, Construction and Building Materials, v. 212, 2019, pp. 531–540

Arthur Cheung et al., “Short Guide to Maintaining your Historic Building”, Hong Kong Institute of Surveyors, 2023.

Ancient House Group of the Cai Clan, 44th Session of the World Heritage Committee, United Nations Educational, Scientific and Cultural Organization, 2021.

Dazhi Liu and Yupeng Wang, “Red Civilization-Terracott Red Brick”, Arts Studies and Criticism, v.4, no.1, 2020. 

Fenghua Jin, Zhaoyi Ye and Jin Tao, “Research on the color of ancient residential architecture in Southern Fujian and its inspiration for modern urban color application,” 2016 International Conference on Civil, Structure, Environmental Engineering (I3CSEE 2016).

Zhaoyi Ye and Jin Tao, “A Study of Traditional Villages and Red-Brick Residential Dwellings in Xiamen”, 2022 International Conference on Humanities and Education (ICHE 2022). 

Qiang Wang, Legendary Port of the Maritime Silk Routes: Zayton (Quanzhou), New York: Peter Lang Publishing, 2020.