Researchers and restorers rely on knowing the original colors laid by the painter. Over the years, factors such as temperature, humidity, and even microbial activity can alter hues, sometimes reversing them. Recreating the original idea is challenging, but today the Joint Institute for Nuclear Research (JINR) physicists apply several non destructive techniques: X‑ray fluorescence analysis (XRF), electron microscopy, infrared and Raman spectroscopy, and neutron activation analysis, which stands out as the most precise method.
Each facility begins with a field assessment using a portable XRF device. By analyzing the painting on site, experts obtain a clear view of the elemental composition and identify the pigments used in most cases directly on the wall.
“A portable spectrometer lets us name the elemental makeup right there. Certain elements reveal pigment pigments: mercury indicates cinnabar in red paint, while a high iron content points to red ocher. The spectrometer penetrates a depth that reveals all layers down to the plaster. Yet this shows only the general composition, like colors mixed together. A sample is taken for laboratory analysis to accurately separate the pigments,” explains Olga Filippova, Senior Investigator of the Neutron Activation Group in the JINR Neutron Physics Laboratory.
Stratigraphy, or layer analysis, reveals how many layers exist in a sample. Polarized microscopy distinguishes pigments by optical properties, and infrared spectroscopy helps identify the binder type, whether egg white, animal fat, or other components. Microchemical analyses also take place in the laboratory.
Neutron activation analysis is employed to study frescoes with greater precision in the laboratory. The sample is placed in a neutron stream, triggering nuclear transformations that are recorded by spectrometric equipment. The resulting spectrum is processed to determine the exact elemental makeup. Most elements can be quantified with precision from one atom to one million; for elements like gold, the accuracy can reach one to one billion. Based on the elemental composition, researchers infer the materials used, including pigments and plasters,
Yet precision comes at a cost: it takes about one and a half to two months from sampling to the first results.
These methods have already been applied at various cultural sites in Veliky Novgorod, Pskov, and Moscow.
Black jacket turned red
In Veliky Novgorod, investigators examined the 12th‑century St. George’s Abbey. Historically, the saint’s cloak was depicted in red, but in a current view it appears black-brown with patches of bright red. What caused this inconsistency puzzled art historians for some time.
Analysis of the basic composition revealed a notable lead content, pointing to unstable white lead. It is this pigment that later darkened the fresco. “Some pigments reverse color under varying conditions. White lead starts bright, but shifts to black as temperature, moisture, and microbial activity change,” notes the team. A pigment of this kind in St. George’s image explains the cloak’s unusual color, and a digital reconstruction helped approximate the original appearance.
Black and white
In the Smolensky Cathedral of the Novodevichy Convent in Moscow, the drum of the cathedral shows archangels in yellow, green, and red robes. White elements and red garments display a striking contrast. The composition revealed high lead content in the black strips, indicating the use of white lead or lead carbonate. This compound is not highly stable against heat, humidity, or certain bacteria, and over time it tends to turn into almost black lead oxide.
Instances of darkened monuments appear across Russia, Georgia, and Europe. The investigation showed that the black folds in red garments contained altered white lead, while white folds in other colors were painted with solid whitewash. Based on these findings, the fresco fragment was digitally reconstructed to show that all colors were originally presented in a unified style.
The true style of the Greek Theophanes
At the Church of the Savior painted by the renowned Greek Theophanes on Ilyin Street in Veliky Novgorod, the works already appear black and red, nearly monochrome. Art historians have long debated whether this palette was the artist’s deliberate choice or the result of environmental influences.
To shed light on the question, researchers examined another monument, the Simeon the God‑Receiver church of the Zverin Monastery, where some areas show unusual color choices such as a red halo. Temperature experiments established a color-temperature scale for primary hues, enabling digital reconstructions of individual fresco parts. A forthcoming publication will detail these findings.
Further study of a fresco depicting three apostles from the Simeon church showed that heat can turn yellow ocher red within minutes, aligning with the 1471 date when the church burned during Ivan’s siege of Veliky Novgorod. This suggests a plausible cause for the color changes observed in the fresco.
Kremlin riddles
Today, researchers collaborate with art historians and restorers at the Assumption Cathedral inside the Moscow Kremlin to determine the true color palette of the frescoes, perform digital reconstructions, and verify how each color altered over time. The work also supports the verification of 17th‑century tender documents.
According to the restoration team, the challenge lies in past restorations that did not preserve original appearances. In the 19th and early 20th centuries, restorers sometimes added contemporary materials, giving the old paintings a darker, more somber look. The 17th‑century works, in reality, were bright and radiant.
Experts note that gilding age can be determined by XRF comparisons with known examples from different centuries. This allows researchers to infer the era of various illuminations and set up connectors in the lab to refine dating in the restoration process.
As researchers explain, understanding the composition of mixtures on the painted surface and how they relate to purchased materials helps verify historical documents as part of a broader scientific task.