Working diligently to remove a gray salt layer from a million individual pieces of glass, three Czech conservators and a UCLA scientist have been restoring a renowned mosaic in central Europe.
Materials science is forging its way into the future with new technologies in metallurgy, optics and nanotechnology – but one of its more surprising applications is its recent marriage with the world of medieval art.
UCLA Professor Eric Bescher has been traveling to Prague for a decade now, applying a material he and his colleagues created to a mosaic titled “The Last Judgment.” The application of the substance, called sol-gel, is meant to prevent weather corrosion that could cause the pieces to be obscured forever.
Bescher traveled to Prague for annual maintenance last week and will be returning again in the next month.
The materials science professor returns to the Czech capital every year to remove and reapply the top coating so that the sol-gel remains effective in battling atmospheric corrosion.
Sol-gel is often used as a protective coating, as an outer layer on sunglasses or on aircraft windows, but the UCLA team’s application of sol-gel to art conservation is unprecedented.
“Sol-gel has been proposed as an alternative conservation treatment for corrosion, but its not been used to the extent that we have used it,” Bescher said.
“The Last Judgment” spans 10 meters by 13 meters above the south entrance of the St. Vitus Cathedral, which resides inside the sprawling grounds of the Prague Castle in the Czech Republic.
The mosaic is composed of three panels. The central panel depicts Jesus Christ surrounded by angels gazing down at Czech patron saints and the royal family.
The two side panels depict scenes from heaven and hell.
“The mosaic has a huge symbolic significance in the Czech Republic. It is located right in the center of power. ... It is a huge work of art, not just physically, but also symbolically,” Bescher said.
Czech conservators have been attempting to conserve the mosaic with organic polymers, the building blocks of synthetics, since the 1950s, but these materials could not withstand ultraviolet radiation and gases from the atmosphere, Bescher said.
The Getty Conservation Institute contacted Bescher and retired professor John Mackenzie of the materials science department at the Henry Samueli School of Engineering and Applied Science at UCLA in 1992 to develop a new material technology to conserve the 14th-century glass mosaic that lay hidden under layers of corrosion caused by gases in the atmosphere.
“(The Getty Conservation Institute) said they had been all over the world and nobody was able to put a successful coating on the glass,” Mackenzie said.
Over the span of three years, Bescher and Mackenzie developed a successful multi-layer coating composed mostly of sol-gel and covered with a removable top layer made of a traditional polymer, and tested it in UCLA labs.
The results were successful and were soon tested at Getty labs under extreme weather simulations, considering that Prague winters reach approximately minus 20 degrees Celsius, Bescher said.
Unlike polymers, sol-gel’s ceramic nature allows it to resist the effects of weather and corrosion more easily, and its liquid form makes it simple to apply. It has the same consistency as paint and can be applied with a small brush, Bescher said.
“Sol-gel is a process by which you can make a ceramic at or near room temperature starting from a liquid, which is different from the traditional way of making ceramics, which usually involves firing at very high temperatures” Bescher said.
Working with the Office of the President in the Czech Republic, in 1998 Bescher began applying the sol-gel to the 1 million square-inch pieces of glass, called tesserae, that had to be coated by hand without applying any sol-gel to the material between the pieces.
The sol-gel layers underneath the top polymer layer are estimated to last for 25 years. After that time Bescher predicts that he will need to return to fully remove and reapply all sol-gel layers.
Besides employing his scientific knowledge of materials, Bescher said he had to learn about the concerns of art conservators.
“We had to worry about the way the mosaic looked. You can’t make a mosaic look like it was just made yesterday; you have to make it look like it is 700 years old,” Bescher said.
The mosaic was also originally gilded; therefore, Bescher and the Czech conservators had to carefully insert tiny pieces of gold foil into each tesserae, according to the Prague Castle Web site.
All three panels have been finished, and the mosaic was reopened to the public in 2003.
Look for Science & Health articles every Tuesday and Friday.