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Conserving Mosaics: A Nod To The Chemistry Nobel Prize

When blogger David Bradley posted this lovely image of a Moorish mosaic, I knew I had to learn more about how tile art is conserved.

In honor of today’s Nobel Prize in chemistry to Dan Shechtman for the discovery of quasicrystals, I thought I’d write a little post on the world of mosaic art conservation.

Bear with me–there is a connection.

(This is precisely what I said when Paula Artal-Isbrand, a mosaics conservator at the Worcester Art Museum, answered the phone. Luckily, she didn’t deem me a random freak and then hang up.)

OK. So back to the Nobel Prize. Quasicrystals are regular patterns of atoms that never repeat themselves, much “like the fascinating mosaics of the Arabic world,” noted the prize’s press release.

This got me thinking–and blogger David Bradley too—because moments later he tweeted the perfect Moorish mosaic example you see here. And I knew I had to learn a bit more about mosaic art conservation and restoration.

So here it goes: Tiles in mosaic art can be made of a serious potpourri of materials, such as glazed terracotta (in the case of many Moorish mosaics), as well as stone, glass, porcelain, marble, metal and wood.

Compared to paintings, paper and textiles, mosaics are relatively sturdy, and not particularly susceptible to problems like light degradation, Artal-Isbrand told me. But that doesn’t make them immune to the elements, particularly because many pieces are stored outside as part of buildings.

For example, freeze-thaw cycles can lead to tile and mortar cracking. Bacteria and fungi growing on the surface of these artworks can deposit ugly stains from their excretions that stay behind even after the microbes are wiped away.

Worse is when there’s a crack in a tile which permits water to seep in, and thus creates a cozy home for microbes below the glaze—entirely out of reach for conservators.

If the mosaic’s tiles or mortar have calcium carbonate as an ingredient (and many do), roots of plants and trees will try to extract the mineral, which is also problematic, Artal-Isbrand explained.

But one of the major problems faced by mosaic conservators is the fact that there are often lose chunks at the edges of the artwork, which museum or archeological-site visitors are tempted to take home as a souvenirs. “They really need to be guarded,” she said.

I asked Artal-Isbrand if conservators ever add protective coatings to mosaics. It turns out she had recently finished a project to remove unnecessary

protective coatings—added decades ago—from a large Roman floor mosaic originally from Antioch which is currently housed at the Worcester Art Museum.

(Roman floor mosaics are mostly made of stone, although they also used glass on occasion, Artal-Isbrand explained. That is until the Romans realized glass dissolved with time.)

Back in the day (I’d guess the 1960s) when the world believed that plastics could do no wrong, conservators had added layers of acrylic and polyurethane on top of the mosaic.

Unfortunately the polyurethane yellowed unappealingly with time. To boot, the mosaic below “doesn’t actually need any protective coatings, since they are stored inside away from the elements,” she said.

After the project was over, the museum decided to stop allowing visitors to walk on the mosaics—which they had permitted for decades—to ensure the mosaic stayed in good shape.

All in all, this was a good idea, Artal-Isbrand said, but she added that the Roman mosaic had once made “a wonderful dance floor” during old-school galas at the museum. I can just imagine!

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