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Mosaic Conservation in an Ancient Site



Many people walk around ancient ruins looking up at stone columns or old sculptures. Thomas Roby, a mosaic expert, is usually looking down at the floor, where the designs, made with thousands of tiny, inlaid stone tiles, were set down centuries ago.

Based in Los Angeles at the Getty Conservation Institute, Mr. Roby travels several times a year to Tunisia. He runs a training program there teaching mosaic-preservation techniques to workers from around North Africa. The region abounds with ancient sites and mosaics dating back to the Roman and Byzantine eras. Mr. Roby is part of a project called Mosaikon, an international collaboration of foundations trying to preserve these sites. He is launching another training program in Morocco this fall.

Along with his personal suitcase, Mr. Roby carries a large, hard-shell Pelican case for work tools. He lugs training materials and handbooks printed in English, French and Arabic. The people who attend his courses are usually employed at historical sites as guards, tour guides or workmen. “We’re taking people who have good manual skills but not much formal education and training them in the maintenance of mosaics on site,” Mr. Roby says.

Since 2010, he has been holding monthlong workshops at Bulla Regia, a Roman site in northwestern Tunisia that dates back to the first century A.D. It is known for having about 400 elaborate mosaics. Mr. Roby spends most of his days outside in desert temperatures, often wearing a straw hat favored by Tunisian farmers and a pair of cotton painter’s overalls.

Preserving mosaics involves cleaning between individual tiles, called tesserae, scraping off lichen or moss, resetting them if they are loose, and filling in the spaces with lime mortar. Mr. Roby’s toolbox is full of precision instruments: dental picks, scalpels and large tweezers. He uses an air bulb to blow away dirt. Some situations, when he has to remove old cement repairs, for example, demand more aggressive measures, and he will use a hand drill, hammer and chisel. Reinforced cement was popular decades ago but it can damage the tiles over time and is no longer used by conservators, he says. A kneeling pad protects his kneecaps during hours on uneven stone tiles.

Once the tesserae are clean, he stabilizes them by injecting liquid mortar with a large veterinary syringe or resets them using a set of hand-forged steel spatulas made in Italy. Mr. Roby likes to point out that he makes mortar in much the same way the ancient Romans did—he mixes quicklime and water to make putty then thickens it with sieved sand and crushed stone. He uses old film canisters as measuring cups and a natural sponge to wipe excess mortar off the tiles.

After a mosaic has been stabilized, sometimes the best way to protect it is to rebury it under sand and gravel, he says. “At Bulla Regia, for example, the government doesn’t have the resources to care for hundreds of mosaics, so we rebury a large number so that others can be properly maintained and presented to the public,” he says. Mr. Roby carries electronic data sensors to measure underground temperature and humidity when reburying mosaics.

Mr. Roby grew up in Philadelphia and studied archaeology in college, earning graduate degrees in architectural history and historic preservation. He says he fell into mosaics while working on excavation projects. He was interested in stone preservation and came to appreciate the complexity of mosaic art. “What’s impressive is how the variety of stone colors can be used like a painter’s palette to create a rich, nuanced image,” he says.

Mr. Roby’s last workshop in Tunisia was in May. Last week, a course scheduled for November was postponed until spring due to security concerns, he says. The country has had two terrorist attacks this year. In March gunmen opened fire at the Bardo National Museum in Tunis, and in June there was a deadly attack at a beach resort near Sousse. But Mr. Roby points out that conservation work continues in more dangerous places, including Syria and Libya.

Recently, a Libyan trainee who had attended last spring’s program sent photos from a site he was working on in the eastern part of the country. Mr. Roby says he usually tries to follow up with attendees’ progress by visiting their home sites. “But in the case of Libya, that’s been impossible, so it was particularly gratifying to see those photographs,” he says.

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