Cologne Cathedral's Darkened Exterior: Why It's Black

Cologne Cathedral is a Gothic masterpiece and cultural heritage site. It is Germany's most visited landmark, attracting an average of 6 million people a year. The cathedral is known for its architectural superlatives, but the extensive vandalism it has to endure is equally fascinating. The sandstone that comprises most of the cathedral reacts with the sulphuric acid in the rain, turning dark grey and giving the cathedral its distinctive colour. This is why repaired sections look much lighter than the rest of the building. The black patina has been a characteristic feature of the cathedral for centuries and is due to weathering, soot, and biofouling.

The sandstone used in construction reacts with sulphuric acid in the rain

The sandstone used in the construction of the Cologne Cathedral reacts with the sulphuric acid in the rain, which, over time, turns the stone a distinctive dark grey. This process began in the Industrial Age, and has continued to affect the building since. The sandstone used in the construction of the cathedral is not inherently black, but has been discoloured by the effects of air pollution and acid rain.

The Schlaitdorf sandstone, used from 1842 onwards for the transept facades and the upper parts of the nave and transept, is particularly susceptible to weathering. This type of sandstone is constantly being renewed and, until the 1980s, was replaced with Londorf basalt lava. This basalt lava is considered very weather-resistant, but is grey in colour, rather than the original sandy beige. Since the 1990s, restorers have attempted to use stones that match the original sandstone as closely as possible.

The sandstone's discolouration is not the only factor contributing to the cathedral's dark appearance. The building is also affected by soot and biofouling. The cathedral's statues and sculptures, made from materials such as limestone, also require extensive conservation work.

The cathedral's distinctive colour has become a characteristic feature of the building, and there are plans to maintain this appearance. The original sandstone has suffered due to environmental influences, and a harsh clean would cause further damage. The building's current colour is also part of its character, and it would be a shame to lose this unique aspect of the cathedral.

Soot and weathering have created a black patina

The black colour of the Cologne Cathedral is due to a combination of soot accumulation, weathering, and biofouling. The soot has built up over the years, leaving a black patina on the cathedral's surface. While the soot has certainly contributed to the darkening, the main reason for the black colour is the type of stone used in its construction.

The cathedral is made from various types of stone, including trachyte, sandstone, and limestone. The sandstone, in particular, is susceptible to weathering and has turned increasingly black over time. The soft sandstone acts as a primer for modern artwork, attracting vandalism and graffiti. The sandstone's bright yellow colour has been almost entirely obscured by the black patina, a result of air pollution during the industrial age.

The cathedral's location in an urban area has exposed it to high levels of pollution, including acid rain. The sulphur content of the air, as well as bird droppings, have accelerated the deterioration of the stone. While efforts have been made to reduce air pollution in recent decades, the damage to the cathedral is already extensive. The combination of soot and weathering has created a unique patina that has become a characteristic feature of the Cologne Cathedral.

In addition to the stone type and pollution, the cathedral's intricate design with numerous nooks and crannies has made it challenging to clean and maintain. The building's many small figurines and towers would make the cleaning process incredibly costly and time-consuming. As a result, the black patina has been left largely untouched, preserving the iconic appearance of the Cologne Cathedral.

The cathedral is built from different types of stone

The Cologne Cathedral is built from several different types of stone, including trachyte, sandstone, and limestone. The black patina of the cathedral is the result of several factors, including weathering, soot, and biofouling. The use of different types of stone with varying colour gradations contributes to the overall dark appearance of the cathedral.

The original construction of the cathedral began in 1248 and was completed in 1880, following a long period of interruption. The cathedral is a testament to Gothic architecture and is one of the tallest churches in Europe. Standing at a height of 157 meters, it is the second-largest building in Cologne and the city's most popular tourist attraction.

The different types of stone used in the cathedral's construction have varying levels of durability and resistance to environmental influences. The sandstone, in particular, has suffered damage over time. The intricate details and numerous small figurines and towers on the exterior of the cathedral make cleaning and maintenance a challenging and costly endeavour.

The black patina has become a characteristic feature of the Cologne Cathedral, and some people believe that it should be preserved as part of the cathedral's character. The dark colour is also practical, as the soot and grime help to create a consistent appearance throughout the building, disguising the varying colours of the different types of stone used in its construction.

The cathedral's master builders have explored various methods for preserving the stone, but a convincing solution has not yet been found. The iron anchors and dowels holding the architectural decorations are also starting to rust, threatening to crack the stones and requiring replacement with steel parts.

The cost of cleaning the cathedral would be too high

The cost of cleaning the Cologne Cathedral would be too high. The cathedral is a massive structure, standing at 157 metres tall and attracting an average of 6 million visitors per year. It is a complex building with many nooks and crannies, small figurines, and small towers. The sheer size and complexity of the cathedral would make any cleaning efforts incredibly costly.

The cathedral is also constructed from various types of stone with different colour gradations. The black soot that has accumulated on the cathedral over the years is the only thing that keeps the building's colour consistent throughout. If the cathedral were to be cleaned, the different colours of stone would become apparent, resulting in a "dappled" appearance. To restore a consistent colour, stones of minority colours would need to be removed and replaced with stones that match the majority colour. This would be an extremely expensive and time-consuming process, requiring the expertise of stonemasons and stone sculptors.

Additionally, the cathedral is constantly in need of repair and maintenance due to the effects of wind, rain, and pollution on the stone structure. The cost of these ongoing repairs is already substantial, with maintenance costs of around €30,000 per day. The cathedral's master builder, Barbara Schock-Werner, famously stated: "Cologne Cathedral without scaffolding is not a pipe dream but a nightmare. It would mean that we would no longer be able to afford the cathedral." This highlights the significant financial burden associated with the upkeep of the cathedral, and cleaning it would only add to these costs.

Furthermore, the sandstone used in the cathedral is particularly susceptible to weathering and pollution. The Schlaitdorf sandstone, used from 1842 onwards for the transept facades and upper parts of the nave and transept, shows the most intensive weathering and requires constant renewal. While other types of stone, such as Londorf basalt lava, are more weather-resistant, they do not match the original sandstone colour. The cathedral master builders prefer to use stones that are as close as possible to the original, adding to the complexity and cost of any cleaning or restoration efforts.

In conclusion, the cost of cleaning the Cologne Cathedral would indeed be too high. The size, complexity, and variety of materials used in the cathedral contribute to the challenge and expense of cleaning and maintaining the structure. The ongoing need for repairs and the susceptibility of the sandstone to weathering further increase the financial burden. As a result, the iconic black patina of the cathedral, formed over centuries due to weathering, soot, and biofouling, is likely to remain a defining feature.

The black colour is now part of the cathedral's character

The black colour of the Cologne Cathedral is due to several factors, including weathering, soot accumulation, and biofouling. The sandstone used in its construction reacts with the sulphuric acid in rainwater, turning dark grey over time. While this patina may have been unexpected, it has undoubtedly become a defining feature of the cathedral, adding to its character and sense of mystery.

The dark colour of the cathedral has captured the imagination of many. It stands out from other buildings in the city and has become an iconic part of Cologne's skyline and identity. The black colour creates a sense of intrigue and allure, inviting visitors to explore its nooks and crannies and discover its secrets. Over the years, the cathedral has become synonymous with this dark hue, and it has become an integral part of its overall aesthetic and allure.

The cathedral's black exterior also serves as a testament to the passage of time and the endurance of the structure. It is a physical manifestation of the cathedral's long and complex history, bearing the marks of the Industrial Age and the challenges of preservation. The patina tells a story of resilience and transformation, reflecting the ever-changing world around it while remaining a steadfast presence in Cologne.

The black colour has also inspired artists and creatives, providing a unique backdrop for modern artwork and expressions of individuality. While some may view the coating of black dirt as vandalism, others find beauty in the contrast between the dark exterior and the vibrant interior spaces filled with colourful stained glass windows and intricate carvings.

The Cologne Cathedral's black exterior has become an essential part of its character and charm. It is a reminder that even the most unexpected features can become beloved and celebrated aspects of a structure's identity. The cathedral's ability to embrace and embody this unique characteristic showcases its enduring appeal and cultural significance.

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