Researchers have discovered that atomic oxygen, a highly reactive gas found in space, could provide a breakthrough solution for restoring damaged Old Master drawings that have been darkened by pollution. The innovative approach represents a major advancement in art conservation, offering hope for thousands of artworks that have become too degraded for public display.
Conservators at the Statens Museum for Kunst (SMK) in Copenhagen first noticed the alarming problem in the early 2000s. White highlights on masterpieces by renowned artists including Hans Holbein, Abraham Bloemaert, and C.W. Eckersberg were darkening at an unprecedented rate. The discoloration was so severe that many works could no longer be exhibited to the public, as they had lost their original meaning and appearance.
"When the drawings are in that condition, they cannot be exposed to the public anymore because they lose, in a way, their meaning and their appearance and so they are not suitable for display," explains Gianluca Pastorelli, a conservation scientist at SMK who has been leading research efforts alongside Niels Borring for multiple decades.
The scope of the problem is significant at SMK, which houses one of the world's largest drawings collections with approximately 18,000 works dating back to the late 15th century. Of the museum's 800 works created with chalk, charcoal, or pencil and painted with lead white highlights, about half have experienced some degree of discoloration. Additionally, 200 salted prints and lithographs from Copenhagen's Royal Library have been similarly affected.
The mystery deepened when researchers discovered that not every artwork showed signs of darkening, even those created by the same artist during the same time period. Curiously, oil paintings rarely exhibit this type of degradation, which puzzled scientists and conservators alike.
Lead white pigment has been the preferred choice for artists since ancient times due to its brilliant white color and unique properties. However, its use declined in the 20th century when toxic health effects became widely known. Throughout history, the sourcing and production methods of lead white have evolved, but it was traditionally mixed with binding agents and applied to artworks with brushes.
To solve this conservation puzzle, Pastorelli's research team employed cutting-edge, non-destructive imaging technologies including X-ray fluorescence, X-ray powder diffraction, and microsampling lead isotope analysis. These advanced techniques allowed them to essentially fingerprint the paint compounds, identify material properties, and analyze the chemical makeup of the darkened areas without causing further damage to the precious artworks.
Their extensive research revealed that changing manufacturing techniques and variations in the chemical composition of lead white pigment affected the artwork's vulnerability to degradation. Most significantly, they discovered that chemical reactions were converting the lead white into lead sulfide, also known as galena, a well-known metallic-gray mineral. Microscopic cross-sections of damaged areas showed that this conversion was occurring primarily at the surface level.
The culprit behind this degradation was identified as airborne sulfur-containing compounds. Sulfur pollution is a byproduct of modern industrial society, originating from vehicle traffic, industrial processes, and even human digestive gases. These pollution levels have increased dramatically since the Industrial Revolution, creating an increasingly hostile environment for historic artworks.
At SMK, a move to temporary storage conditions partially contributed to higher sulfur exposure levels and more noticeable darkening. However, the early 2000s marked a particular turning point in the degradation process for several environmental reasons.
"We have to also remember that in 2003 to 2004, we started to have very hot summers and this has an impact on the amount of pollution that is produced from traffic or factories, and also it makes it more challenging for climate control systems inside museums and their filtering system to handle all the variables that must be limited to a certain range," Pastorelli notes. Heat and increased pollution create ideal conditions for chemical reactions to occur more rapidly and extensively.
The reason oil paintings are largely spared from this type of damage became clear through the research. "We believe lead white darkening is much less frequent on paintings largely because many paintings use oil paints, and oil indeed has a strong protective effect on lead white pigments," Pastorelli explains.
Traditional conservation treatments for this type of damage include hydrogen peroxide baths or gels designed to lighten the darkened highlights. However, these conventional methods carry significant risks of damaging the original materials and chemically create new compounds, which violates conservation principles. Tomas Markevicius, an art conservator and founder of the Moxy Project research initiative, compares these treatments to outdated medical approaches: "It is like an old-school cancer drug—it treats, but it also destroys."
Markevicius and his team, which includes Pastorelli, are pioneering an entirely revolutionary approach using atomic oxygen. In May, at a conference in Perugia, he presented the first-ever successful use of atomic oxygen to reverse lead white darkening on laboratory mockups—without using water, acids, or direct contact with the artwork. He describes this achievement as "a major breakthrough in both chemistry and art conservation."
The space-age connection is quite literal. Atomic oxygen is a highly reactive form of oxygen naturally found in low Earth orbit, where it readily interacts with surrounding chemicals. NASA scientists Sharon Miller and Bruce Banks initially researched how this disruptive gas would impact spacecraft exteriors before later studying its potential applications for cleaning cultural heritage items.
"Upon contact with atomic oxygen, organic materials like soot, stains and varnishes release into the air. They get converted to carbon monoxide and carbon dioxide and leave as a gas, so they don't leave residue on the surface," Miller explains.
The NASA scientists had an opportunity to test their atomic oxygen technology on an unusual conservation challenge. At a 1997 event organized for the fashion brand Chanel at the Andy Warhol Museum in Pittsburgh, a careless guest defaced Warhol's hand-painted "Bathtub" (1961) with a lipstick-laden kiss. When conventional treatment methods failed to remove the makeup, Miller and Banks employed an atmospheric oxygen beam for more than five hours. The treatment successfully removed the lipstick smudge, along with some underlying grime and a thin paint layer.
Markevicius's Moxy group is now developing atomic oxygen technology as part of a green cluster initiative in cultural heritage, backed by the European Union to develop sustainable conservation technologies. The ambitious project aims to produce a laboratory-scale prototype by late 2026, with researchers rigorously testing mockups and physically sensitive materials with various types of contaminants to optimize treatment protocols.
For now, SMK is focusing on ensuring that its climate control and air-filtering systems operate at maximum efficiency. However, the museum is not currently taking action to lighten the darkened highlights in affected works because no completely safe technique exists yet. "It's a strong driver to develop such technologies that would have the least impact upon these incredibly valuable but also incredibly fragile structures, which are unique," Markevicius emphasizes, highlighting the urgent need for innovative conservation solutions that can preserve our cultural heritage for future generations.
