Two-Faced Microbes: Dirty Fungi And Cleaning Bacteria

Microbes can be an ugly pain-in-the-butt for artifacts. Even if the bacteria and fungi growing on heritage buildings, frescoes, space suits and archival documents can be killed, they often leave behind some rather unpleasant stains that are really hard to clean off the sensitive surfaces of artifacts. That's the situation in King Tut's tomb, for example, where fungi have left behind dark brown spots on the beautifully painted walls. Today the Harvard Gazette wrote about this issue: At the request of Egyptian heritage officials, researchers at the Getty Conservation Institute swabbed the walls of King Tut's tomb, and sent samples of the brown muck to Ralph Mitchell, a Harvard microbiologist who specializes in cultural heritage science. Getty chemists figured out that the dark spots are actually melanin--the same pigment that builds up in your skin when you get a tan--while Mitchell's team figured out that the fungi are dead and probably won't be producing any more browny spots. Mitchell thinks that the fungi initially grew because the tomb was sealed before the paintings inside were dry, suggesting that the teenage king was buried in a hurry. The still-wet surface thus provided tempting real-estate for melanin-producing fungi. It turns out that melanin-producing fungi have also stained marble in Italian cathedrals after an ill-advised attempt to protect the marble using acrylic polymers. The acrylic on the marble attracted the staining microbes who found the plastic to be a tasty meal. But microbes will also grow on buildings, art and artifacts that haven't received unwise "protection." For example, orangey carotenoid pigments are often left behind by bacteria on stone buildings, Mitchell says, and frescoes have been stained rosy red due to the phycoerythrin pigments produced by cyanobacteria. The question remains: How does one remove these unfortunate discolorations? Mitchell is developing a technique that uses enzymes to eat away the unpleasant pigments without hurting the pretty parts below. Think of laundry detergents that advertize enzymes which can remove stains on your white clothing without doing damage to the textiles. Mitchell's strategy obeys the same overall principle... and that's about as much information as he was able to give because he's in the middle of patenting the enzyme cleaning process. So, all this could leave you with the impression that microbes are only bad for cultural heritage, but here's a possible counterpoint: Researchers in Italy and Spain are experimenting with the idea of using bacteria to clean off the salty crusts that build up on frescoes. Sort of weird but true: The researchers grow Pseudomonas bacteria in a wet gel, and apply it to the frescoes. The bacteria then get to snacking on the...

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Digital Restoration: Introducing An Undo Function?
May15

Digital Restoration: Introducing An Undo Function?

Every once in a while, well-intentioned attempts to save a valuable painting or artifact from the decay of time bombs pretty badly. Consider the thousand-year-old ancient parchments that were laminated in the late 1950s or early 1960s--during that era's love affair with plastics--in order to protect the valuable documents from the wear and tear of a long life. Four decades later, the yellowed and brittle laminate had to be painstakingly removed from Belgium’s oldest parchment, the Codex Eyckensis, as the decaying plastic began to exacerbate the injuries it had aimed to avoid. Such hard lessons have since pushed conservators to look for easily reversible, minimally invasive ways to protect or restore cultural masterpieces—sometimes opting to shun any interventions altogether. Another possibility is to consider a digital restoration technique that offers “all the benefits of an Undo button,” says Daniel Aliaga, a computer scientist at Purdue University. Aliaga and his Phd student Alvin Law have designed software that can project light images on to sculptures or paintings that, for example, can reveal to the viewer what the decaying masterpiece may have looked like before decades or millennia of deterioration. The projection can also boost faded colours on a painting or touch up decorative tints on a piece of pottery or a sculpture’s exterior. Turn off the projector, and the piece reappears in its current day form. Previous attempts to digitally visualize possible restorations to art simply projected images onto a wall or screen. Aliaga’s digital restoration technique projects images directly on to the art which is tricky to do in 3D, he says. But working with Richard McCoy at the Indianapolis Museum of Art, Aliaga has tried out the technique with ancient pottery from Mexico’s pre-Columbian Casas Grandes style and Neolithic people in China.  He's also given 16th century angel sculptures a digital facelift. Besides visions of what the artwork may have initially looked like, the digital technique could also project more whimsical or educational images. One possibility is to project an X-ray scan of a sculpture that highlights interesting scaffolding or materials beneath the artwork’s surface. Another option is to project the results of so-called infrared reflectography measurements, a non-invasive technique which can reveal features that an artist initially sketched on a canvas but then decided not to include in the final painting. These initial sketches could be projected on to the artwork to show how the painting was initially envisioned. Finally, you could also imagine using the technique to do a little artistic alchemy, such as turning a marble statue into wood using light. Although light projection seems, well, light to the touch, could this digital projection cause damage that would leave...

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