XRF analysis is a tool used by conservators, including at ISGM, to non-destructively examine the materials used in historic art, providing a valuable glimpse into the pigments and techniques employed by artists.
X-ray fluorescence spectroscopy is a mouthful, which is why conservators refer to it as XRF. XRF analysis is a favorite tool of conservators, because it’s quick, doesn’t require a sample (so it’s non-destructive) and can be used to analyze all sorts of materials. XRF identifies the elements that are present in a material, which is especially helpful for characterizing metals and pigments.
At the Isabella Stewart Gardner Museum we are fortunate to have a portable XRF spectrometer that we’ve used to study many of the objects in our collection both large and small: from Titian’s large painting of The Rape of Europa to the miniature illuminations of Jean Bourdichon in the Book of Hours. The portability of our XRF spectrometer means that for objects that are difficult to move, we can bring the analysis to the art.
Isabella Stewart Gardner Museum, Boston (6.T.1). Photo: Jessica Chloros
Analyzing a page from the Book of Hours by Jean Bourdichon with portable x-ray fluorescence (XRF) spectroscopy, 2014.
Recently a collaborative technical study, which included the use of XRF, was undertaken with colleagues from the National Museums of Scotland (NMS). We focused on the 13th-century painted and gilded wood sculpture of Saint Agnes from the Gothic Room. The goal of the study was to learn as much as possible about the materials and techniques used to create the Saint Agnes sculpture and compare it to a painted and gilded wood Madonna and Child sculpture in the NMS collection. Both the Saint Agnes and the Madonna and Child sculptures have been attributed to the same Italian artist, The Master of Saint Catherine Gualino. However, while the substantial scientific analysis we gathered adds much to our understanding of these two sculptures, the results weren’t enough to tell us for sure if the same artist created both pieces.
Isabella Stewart Gardner Museum, Boston (S30s37)
Attributed to the Master of St. Catherine Gualino (Italian), Saint Agnes, about 1315 CE. Polychromed and gilded poplar, 131.4 x 27.3 x 18.7 cm (51 ¾ x 10 ¾ x 7 ⅜ in.)
Last year, the Gardner collaborated with the Smith College Museum of Art (SCMA). In preparation for the upcoming exhibition at SCMA, “Brought to Life: Painted Wood Sculpture from Europe, 1300-1700,” four of the sixteen painted wood sculptures were selected for conservation and technical examination. “Brought to Life” investigates the materials, techniques and reception of painted wood sculpture in Europe between the 13th and 18th centuries. Painted wood sculptures from this time and place often represent sacred figures from Christianity. As objects of prayer and devotion, the sculptures were created to look alive. Historical accounts recorded several instances of such sculptures appearing to speak, bleed, move or cry. Teams of specialized artists collaborated on these sculptures in workshops by first intricately carving blocks of wood and then adding paint and gilding (gold decoration). The painted and gold decoration seldom survives fully intact, either due to repainting (sometimes repeatedly), fading, loss, or changes in taste that led to the removal of pigment and gold on the surface.
One of the key themes of the exhibition is how conservation and technical analysis play an important role in our understanding of these sculptures today. SCMA has no in-house conservation lab or conservators but consulting conservator Valentine Talland (former Senior Objects Conservator) brought in Jessica Chloros (Objects Conservator) and Greta Llanes (Conservation Technician). Together they studied the four sculptures selected for conservation and technical examination: the Falconer, The Circumcision of Christ, Saint Ursula and the Virgin Martyrs, and Saint Fiacre. XRF analysis of the Falconer revealed, among other things, that the flesh was painted with vermilion mixed with lead white, the tunic is painted with lead white and the black and gold decoration is gold leaf applied on top of tin leaf.
The very same materials were found on the Gardner Museum’s Saint Agnes and in fact, the gold-layered-on-tin technique has been found on another sculpture at the Museum, a painted terracotta sculpture of the Virgin Adoring the Christ Child by Matteo Civitali, about 1480. Gold leaf is incredibly thin (about 0.1 µm); when it wears away, the tin leaf is exposed to the environment and turns black with corrosion. Viewed under a microscope, the cross section image clearly shows the difference in thickness between the gold leaf and the much thicker tin leaf. Ceninno Cennini describes this very process of making “golden tin” in his famous treatise, The Craftsman’s Handbook Il Libro dell’Arte (written around the turn of the 15th century).
The Gardner Museum’s rich collection of painted and gilded wood sculpture is well-known, and other collections of painted wood sculptures can be found near and far. By comparing SCMA's Falconer to the two Gardner sculptures, we learn that similar techniques were used in a variety of sculptures in different areas and time periods across Europe. The tradition of painted wood sculpture spans several countries and centuries and these objects provide many opportunities for collaboration.