The Darkened Cologne Cathedral: Why No Wash?

The Cologne Cathedral is one of the most visited buildings in Germany, and was once the highest building in the world. However, over its 770-year history, impurities have accumulated on its stone walls, leading to black crust deposits and discolouration. While some restoration efforts have been made, the task of cleaning the cathedral is challenging due to the variety of stones used in its construction. The black soot actually helps to maintain a consistent colour across the building. Additionally, the delicate nature of the sandstone used in the cathedral's construction means that power washing or other aggressive cleaning methods are not suitable, as they could damage the structure.

The cost of cleaning is high

The cost of cleaning Cologne Cathedral is high. The cathedral is a vast building, with intricate details, small figurines, and towers. The sheer size and complexity of the structure make cleaning a significant and costly challenge. The building's construction from various types of stone, including delicate sandstone, further adds to the expense.

Specialised techniques and equipment are required to effectively clean the cathedral without causing damage. In the past, gentle cleaning methods, such as low-pressure microparticle blasting, have been employed to remove black crust deposits and impurities that have accumulated over the centuries. This process requires the expertise of restorers and stonemasons, who must be trained in the proper use of the technology. The cost of labour for such specialised work is substantial.

The maintenance of the cathedral is an ongoing endeavour. Even if a comprehensive cleaning were completed, the building would require constant attention to prevent the rapid accumulation of dirt and grime, especially due to car traffic. The cathedral's location in a busy city centre also contributes to the challenge and cost of maintaining a clean exterior.

In addition to the financial burden, the time required for such an extensive cleaning project is considerable. The process would likely need to be repeated frequently, as the effects of cleaning may not be long-lasting. The cathedral's size and intricate details mean that by the time cleaning is finished, the areas that were cleaned first may need attention again. This continuous cycle of cleaning would incur significant and ongoing costs.

The high cost of cleaning Cologne Cathedral is a significant factor in the decision-making process regarding the building's maintenance. While the accumulation of impurities and discolouration may detract from the cathedral's appearance, the expense of properly addressing these issues is a substantial challenge.

The building is too big

The Cologne Cathedral is a towering structure, one of the tallest buildings in all of Germany. It is a building of immense detail, with countless nooks and crannies, small figurines, and towers. The sheer size of the cathedral makes cleaning a mammoth task.

The cathedral is so large that by the time a cleaning crew finishes at the top, the bottom would be dirty again, and they would have to start all over. The building is so big that it would take an inordinate amount of time and resources to clean. The task would be incredibly costly, and the Diocese of Cologne, the city of Cologne, and the state do not have the funds for such an endeavour.

The cathedral's vast expanse means that cleaning it would be a never-ending task. The building is so tall that specialised equipment and training are required, adding to the expense. The size and complexity of the structure also mean that certain areas are challenging to access, making the cleaning process even more difficult and time-consuming.

The cathedral's immense size, combined with its intricate details and varied composition of stones, presents a unique challenge for cleaning and maintenance. The task is not only expensive and time-consuming but also requires specialised techniques and equipment to ensure the building's integrity is not compromised.

The stone is delicate

The stone of Cologne Cathedral is sensitive and requires gentle cleaning techniques. The use of power washing or pressurized water could damage and crack the stone. Specialist craftsmen are needed to carefully clean and restore the stone, which is a time-consuming and expensive process.

In 2019, parts of the cathedral's facade were professionally cleaned using a low-pressure microparticle blasting technique. This method involved using a fine aluminium silicate as the blasting abrasive to dissolve the deposits without damaging the original stone. The restorers and stonemasons of Cologne Cathedral were trained in the proper use of this technology to ensure the gentle cleaning of the delicate stone.

The decision to clean the cathedral is complex due to the variety of stones used in its construction. The black soot gives the building a uniform colour, and cleaning it could result in an inconsistent, dappled appearance. The cost and time involved in cleaning such a large and detailed structure are also significant factors.

The stone of Cologne Cathedral is delicate, and its cleaning and preservation require expertise, time, and financial resources. The accumulation of impurities and external influences have resulted in discolouration and deposits, which need to be carefully addressed to maintain the integrity of the stone.

The black soot unifies the building's colour

The black soot that has accumulated on the Cologne Cathedral over the years has resulted in a uniform black colour across the building. The cathedral is constructed from various types of stone with different colour gradations, and the black soot has served to unify the building's colour scheme.

The decision not to clean the cathedral is based on the understanding that removing the soot would reveal the inconsistent colour palette of the underlying stones. This would result in a ""dappled" appearance, with a mix of brighter and darker stones. The black soot, therefore, acts as a unifying element, preserving the aesthetic cohesion of the cathedral's exterior.

Cleaning the cathedral would require a specialised approach due to the delicate nature of the stone. Techniques such as low-pressure microparticle blasting with fine aluminium silicate have been employed in the past to gently remove impurities without damaging the original substance of the facade. However, such methods are time-consuming and expensive, further reinforcing the decision to maintain the unifying effect of the black soot.

The black soot has become an integral part of the cathedral's character and visual identity. Removing it would significantly alter the building's appearance, potentially detracting from its historic charm. The soot-covered exterior has become synonymous with the Cologne Cathedral, and some argue that restoring it to a pristine state would be inappropriate for a structure of its age.

While the black soot unifies the building's colour, it is essential to address the impurities and microorganisms, such as bacteria, algae, and moss, that contribute to the discolouration. These elements can damage the stone and require careful management to preserve the cathedral's structural integrity. Striking a balance between maintaining the unified colour scheme and ensuring the long-term conservation of the building is crucial.

Cleaning is a lower priority

Maintaining buildings can be costly, and with cathedrals, the main struggle is to prevent bits from falling down, so cleaning is a lower priority. While it does happen, it is not a frequent occurrence.

The Cologne Cathedral, for example, has only undergone professional cleaning on parts of its facade. This is because, over the centuries, coal-heating systems, factory chimneys, and steam locomotives have led to the black discolouration of its outer stone walls. The walls have also been covered by microorganisms such as bacteria, algae, and moss, which make the stone appear very dark.

The cleaning process is delicate and requires specialist craftsmen to carefully peel back years of soot and fumes. The cathedral is also constructed from various types of stone with different colour gradations, and the black soot is what keeps the building's colour consistent. If the cathedral were to be cleaned, it would result in an inconsistent, dappled appearance.

Furthermore, the cathedral has numerous nooks and crannies, small figurines, and small towers, making it incredibly costly and time-consuming to clean. The task is so monumental that it seems never-ending, as reflected in the saying, "Once all work is done at the cathedral, the world will come to an end."

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