Recent restoration projects have revealed new dimensions to old Gothic cathedrals. This has been most clearly seen by the world through the restoration process of the Notre Dame Cathedral in Paris, which was damaged after a fire in 2019. 

The restoration was completed last December, revealing a freshly cleaned interior of the cathedral that showed a cream-coloured stone that was much different from the earlier perception of the interior of the Notre Dame as dark and shadowy. 

This restoration — as well as similar restorations in Gothic cathedrals around Europe — makes us wonder about the atmosphere of cathedrals and the science behind their restoration. 

Reviving Gothic architecture: Techniques

Since the start of the modern historical conservation movement and the widespread increase in building restoration, one of its focuses has been on revitalizing Gothic cathedrals. Restoration methods have advanced in modern times with technology. Lasers, sandblasting, and high-pressure water sprays can be used to restore old stone more easily than past methods. 

Each new method has different advantages, but there are still some limitations. The largest limitation of using laser ablation to clean stone is that the lasers cause yellow discoloration in the stonework. The lasers work by heating the layer of grime so quickly that it burns away, which sometimes leaves behind a yellow tint on the stone. However, this can be reduced by adjusting the lasers themselves. 

By changing the pulse duration, some laser modes cause less yellowing in the stone but take longer and ultimately result in a less complete job of cleaning the stone. Lasers with shorter duration pulses — and less expended energy — cleaned more efficiently than lasers with longer duration pulses and also caused more yellowing. Lasers with longer pulse sequences and more expended energy cleaned less efficiently and had less yellowing. 

Micro-sandblasting, which blasts the surface with sand to remove dirt and buildup, can be abrasive to the surfaces of near-millennia-old stone. While laser techniques are not as optimal for preserving the colour of the stone, micro sandblasting can affect the surface texture of the stone. When compared to micro-sandblasting techniques, laser treatment sometimes did not fully remove certain patinas or oxidized coatings, hiding the underlying painted colour in the stone.

Another technique to revitalize Gothic buildings is photocatalytic nanoparticles. These nanoparticles are tiny particles of inorganic compounds like titanium dioxide, which have been used in environmental science because they have the ability to degrade pollutants, like those on the surface of old stone cathedrals. When these nanoparticles are incorporated into a gel, they can also repel water from the surface of the stone, which helps to preserve the quality of the stone. 

One of the best methods for cleaning stone is also the simplest and the oldest: high-pressure water. Using hot, pressurized water with a precleaning treatment of sodium hydroxide and Ethylenediaminetetraacetic acid — a medicinal acid used for treating heavy metal toxicity — has been found to thoroughly clean and reduce black crusts in some cathedrals and was used in the restoration of the Cathedral de Valladolid in Spain. 

These crusts are commonly caused by air pollution. A blend of new and traditional techniques has emerged for cleaning the centuries of grime off of Gothic architecture, with new technological methods used alongside time-tested methods of pressurized water and sandblasting. 

Finding polychromy on old stone

What is revealed with the restoration of Gothic architecture is a newfound appreciation for the many colours that these buildings were painted with. Many parts of Gothic cathedrals — especially statues and carvings — displayed a technique called polychromy, or the practice of using multiple colours to decorate a building. 

Polychromy was often added using stone paints, but over the centuries, much of the paint has worn away. This left formerly polychromic surfaces white or their natural stone colour, which dulled over centuries of usage to the drab greys we associate with Gothic architecture today. New imaging and investigation techniques have been able to detect traces of paint on the walls of Gothic buildings, rewriting our understanding of the true colour of many parts of cathedrals. 

This development is not unprecedented; Greek and Roman statues went through a similar revision. Ancient Greek and Roman statues were once thought to be unpainted and white, inspiring many neoclassical forms, like Canova’s Venus Victrix, to adopt a bright white exterior. 

However, further investigation found that the ancient statues actually had polychromy, as they were painted in a variety of colours. Over centuries, the paint had worn off, giving a sleek white look to the statues that were held up as an ideal of ancient beauty.  

These new developments in the understanding of the art and architecture of Gothic cathedrals are interesting because they have the potential to change how we think about the architecture that surrounds us and the techniques that can be used to preserve it. 

UTSG is full of examples of neo-Gothic architecture, including spaces like Hart House and Trinity College. These Gothic-inspired buildings were often built with darker and unpainted stone. Even without using paint, one look at Hart House shows you that polychromy can be used by varying the types of stone in a building, even if they were left unpainted due to a misunderstanding of what Gothic architecture actually looked like.

The recent restorations of Gothic cathedrals in Europe and the discovery of their vibrant polychromy beginnings highlight the differences between the neo-Gothic buildings familiar to us and the buildings they were inspired by. It challenges our perceptions of what Gothic architecture originally was and whether we seek to duplicate the original or forge our own Gothic style. 

Next time you’re walking through UTSG, see if you can spot the polychromatic faces of our neo-Gothic home!