That last speculation spurred Matthew's colleague Barbara Berrie, a conservation scientist at the National Gallery of Art in Washington, D.C., to reexamine the Venetian paintings that she had been studying for the past few years. Previous analyses of microscopic paint samples taken from a handful of works had revealed many aspects of the artists' techniques, such as their process of layering colors, but art historians had found few recipes detailing how Venetian artists made their colors. "The materials on this inventory list suggested that we needed to look more widely," says Berrie.
Sure enough, when she re-analyzed her paint samples, she found a variety of types of glass particles mixed with the paint.
"It's a very exciting finding," says Jennifer Mass, who heads the conservation-science lab at Winterthur Museum in Delaware, adding that the optical properties of glass might explain the clarity and translucency of Venetian paints, which capture and reflect light in distinctive ways.
These findings and reports by several other conservation scientists imply that Italian Renaissance artists weren't merely painters. They were also experimental chemists who mixed and matched unconventional ingredients. Says Berrie, "They used new materials to create an art for their time."
SILICA GALLERY The presence of glass in Venetian paintings makes sense historically. "During the Renaissance, Venice was the glassmaking capital of the world," says Mass. By the late 15th century, the glassmaking industry was burgeoning, and with it came the creation of high-quality colorless glass, called cristallo, that was prized throughout Europe for its transparency and clarity.
Venetian glassmakers also made a wide variety of brilliantly colored glass objects.
Since Venice was a major port, it received textiles, dyes, ceramics, gems, and other goods from all over the East. These imports inspired the local craftspeople. For instance, to satisfy the Venetians' growing taste for ancient and expensive artifacts, glassmakers figured out how to make fake precious and semiprecious stones out of colored glass. "It was a time of tremendous innovation," says Matthew.
In an age of new ideas, it's no coincidence that Venetian painters exploited novel materials to expand their art. Before Berrie's discovery of glass particles in paintings at the National Gallery, she had some evidence suggesting that Venetian painters experimented with other unconventional materials.
The artist Lorenzo Lotto kept a painting notebook in which he listed materials that he bought. Among them were mercury and sal ammoniac (ammonium chloride), the latter being a white or colorless crystalline salt found in volcanic regions. Although these substances were common in alchemy, Berrie suspects that Lotto used them to adjust his colors.
LORENZO LOTTO - St. Catherine"
Using scanning electron microscopy, energy-dispersive spectrometry, and other sophisticated analytical techniques, Berrie began to explore the glass-in-paint idea. She started with Lotto's 1522 painting "Saint Catherine".
Berrie's microscopic sample came from the sleeve of Saint Catherine's red dress. Viewed in cross-section, the paint can be seen to contain round silica particles 4 microns to 8 microns in diameter that were mixed with red pigments known as lakes.
Upon closer examination, Berrie saw that the silica represented a high-quality form routinely used by Venetian glassmakers. During the Renaissance, they obtained it from quartzite pebbles along the Ticino River in northern Italy. They would then grind the quartzite into a fine powder, says Berrie, who presented her findings at the Materials Research Society meeting in Boston last December.
