Using laser Doppler vibrometry for fresco conservation

Fresco painting, a technique that dates back to antiquity, involves applying dry pigments to wet plaster, creating stunning artwork that can last for centuries. Over time, however, these masterpieces often face degradation due to delamination, where decorative plaster layers separate from the underlying masonry or structural plaster. This deterioration can compromise the structural integrity of the artwork, necessitating restoration efforts.

Historically, conservators have gently knocked on the plaster with their knuckles or small mallets to assess the condition of the fresco. By listening to the emitted sound, they could identify the delaminated areas needing repair. While effective, this technique is limited both by the conservator’s experience and the small number of people in the world who possess these skills.

Recent research by Joseph Vignola at the Catholic University of America is revolutionizing fresco assessment. Vignola and his team have applied laser Doppler vibrometry to locate delamination in the frescos of Constantino Brumidi in the U.S. Capitol building. This innovative method uses a laser to measure the vibration of a surface, enabling the team to detect delaminated areas based on their unique vibrational characteristics.

“By transmitting sound waves to induce motion in the plaster, the system captures vibrational signatures that reveal detailed information about the structural condition of the artwork,” said researcher Nicholas Gangemi.

One of the remarkable aspects of this technology is its ability to identify regions of delamination that may not exhibit any obvious outward signs of damage. The group’s current research focuses on developing techniques to accurately resolve the size and shape of these hidden defects, facilitating precise repairs that will ensure the preservation of the artwork for future generations.

Moreover, advancements in signal processing are enhancing the ability to analyze complex shapes of delaminated regions.

Gangemi presented research related to this work today as part of the virtual 187th Meeting of the Acoustical Society of America, running Nov. 18–22, 2024.

This research explores the simulation of frescoes with known delaminated shapes to validate their methods, ensuring that they can accurately assess and restore the artworks. These fresco surrogates have also offered a platform for Vignola and his team to scientifically validate the dated technique of knocking on a fresco and listening to the sound it makes.

Looking ahead, this research aims to democratize conservation expertise by creating simple, accessible tools. One possibility is to develop smartphone or computer applications that utilize straightforward algorithms, allowing anyone—regardless of their background—to engage with fresco conservation. This initiative not only enhances the preservation process but also raises awareness of the challenges and techniques involved in maintaining these cultural treasures.

As technology continues to bridge the gap between traditional methods and modern science, fresco conservation is poised for a transformative future.

“We are developing techniques to allow us to preserve the artwork for generations to come,” says the researcher.