Smithsonian Science » Museum Conservation Institute

Fungi still visible in wood charcoal centuries after burning

John Barrat — Sat, 13 Mar 2010 23:23:05 +0000

Scientists from the Smithsonian Museum Conservation Institute, the University of Valencia in Spain and the University of Minnesota, recently made an important observation regarding charcoals from wood fires excavated at ancient archaeological sites. They verified that the remains of fungi that had been living in the wood before it was burned could clearly be seen with a scanning electron microscope. Scientists have long known that the carbonization process preserves the anatomical structure of a wood well enough to identify its tree species. Now, new evidence shows that even the fine hyphae, mycelia and other structures of fungi living in the wood often survive the burning process and are clearly evident in wood charcoal. They are preserved well enough that scientists can sometimes distinguish between different fungi groups.

Charcoal analysis, a science known as anthracology, is an area of archaeology that can reveal important information about the wood used by ancient civilizations and, in turn, the users themselves, says Melvin Wachowiak, a senior furniture conservator at the Smithsonian. Knowing what type of fungus infested a wood before it was burned can reveal where the wood came from and why and how it was gathered, say for firewood, a funeral pyre, building a house or other purpose. Dry wood gathered from a forest floor for cooking often has a different fungi content than fresh wood cut and dried for fires or construction. Archaeologists can use this information to better understand wood management strategies of long vanished civilizations and the environment in which they may have lived.

Images: The scanning electron microscope image above shows living brown-rot fungi growing on a fragment of wood. The image at left shows the same fragment with its fungi still visible after the wood has been turned to charcoal. (All images by Magdalena Moskal-del Hoyo)

To confirm their findings Wachowiak and Magdalena Moskal-del Hoyo of the Department of Prehistory and Archaeology at the University of Valencia, burned hardwood and conifer wood samples infested with three primary wood fungi—brown rot, white rot and soft rot—in a laboratory, turning them into charcoal. The fungi were identified prior to burning by plant pathologist Robert Blanchette of the University of Minnesota, a co-author of the study. Then, using a scanning electron microscope, Wachowiak and Moskal-del Hoyo examined the charcoal for visual evidence of the carbonized remains of each fungus. Evidence of all three fungi was visible in the carbonized samples.

Image right: Wood mircostructure and its accompanying white-rot fungi can clearly be seen in this scanning electron microscope image of a charcoal fragment.

The scientists then compared these samples with charcoal taken from ancient archaeological sites: two Neolithic settlements in eastern Hungary, one of the Körös culture and one of the Tisza culture of Polgár-Csőszhalom, and wood from the Bronze Age necropolis of Kokótow in what is now Kraków, Poland. In their research, the scientists were careful to verify that the fungus structures they observed in the ancient charcoal samples had attacked the wood before it was burned and not after.

Other scientists have observed this phenomenon before, Moskal-del Hoyo points out. But this is the first time it has been verified “in a systematic manner,” she says, by using known fungi-infested wood samples, burning them, and then verifying that the same ultrastructure of the wood and fungi are still visible.

A paper on this research “Preservation of Fungi in Archaeological Charcoal” was published recently in the Journal of Archaeological Science. –John Barrat

Problem plastics in museum collections have conservators on alert

John Barrat — Wed, 12 Aug 2009 16:25:32 +0000

While society at large frets about plastics that pile up and seem to last forever— grocery bags clogging landfills and soda bottles washing up on beaches—museums worry about the thousands upon thousands of artifacts in their collections made of plastic, objects that in many cases are crumbling and cracking and sometimes damaging other artifacts as they break down.

“Plastic is a 20th-century material—it is everywhere,” says Jia-sun Tsang, a conservator at the Smithsonain’s Museum Conservation Institute. But most plastics—cheap to produce and adaptable to almost infinite uses—were not created for the ages. “When they get to a museum, it’s our problem. We have to take care of them.”

Photo: Jia-sun Tsang studies a set of 49 plastic samples from a 1920s Lumarith salesman’s kit in the collection of the Smithsonian’s National Museum of American History. (Photo by Donald Hurlbert)

Typical plastic degradation was Tsang’s shorthand for the problem before her. The object of her concern, from the collections of the Smithsonian’s National Museum of American History, Behring Center, was a salesman’s sample kit for a brand of plastic sold under the name Lumarith in the 1920s.

Easily melted and molded into virtually any shape, the product was popular with makers of everything from fountain pens and toys to electrical appliances. But with the passage of years, the kind of plastic used for Lumarith, cellulose acetate, broke down, giving off a telltale vinegar smell. Several of the brightly colored samples in the kit were warped, cracked, and unpresentable.

Tsang and a team of Smithsonian scientists used a variety of noninvasive analytical techniques, including several forms of spectroscopy to pinpoint the molecular structure of the plastic and figure out precisely the cause of the samples’ degradation. Tsang determined that much of the problem was due to leaching of triphenyl phosphate, a fire-retardant compound often added to cellulose acetate to facilitate its softening and flow during the molding process.

Tsang’s study concluded that triphenyl phosphate in cellulose acetate was a particular risk factor for plastic degradation, and that artifacts containing the chemical should not be stored in close contact or in an enclosed space with other cellulose acetate plastics and metals. Case closed, but the larger problem was far from settled.

Photo: This scanning electron micrograph image of a Lumarith salesman’s sample shows fully formed corrosive crystals consisting of oxygen (orange), carbon (green) and phosphorus (purple), as well as a crack in the upper left.

A year-long survey at the American History Museum revealed that many plastics in its collections are from among the five types that museum conservators have identified as “malignant.” Not only are these problem plastics—cellulose nitrate, cellulose acetate, polyurethane, polyvinyl chloride and rubber—more prone to deterioration than other plastics but also their breakdown often produces gases that damage metal, paper or other plastics stored in their vicinity. In most cases, this harmful offgassing can’t be prevented, only slowed, which means degrading plastic artifacts must be isolated from other objects in museum collections.

Photo: Residue from a silicon breast implant stains a storage box at the National Museum of American History. (Photo courtesy National Museum of American History).

Tsang’s specialty is conserving modern paintings and other contemporary art, so a history museum might not seem like her usual haunt. However, before entering the field of fine-art conservation, she was a clinical chemist at the Medical College of Ohio. “Because of my background, I always like to get into the science,” she says. —Mike Lipske

Scientists Determine Geese Involved in Hudson River Plane Crash Were Migratory

John Barrat — Fri, 10 Jul 2009 15:06:43 +0000

Scientists at the Smithsonian Institution examined the feather remains from the Jan. 15, 2009, US Airways Flight 1549 bird strike to determine not only the species, but also that the Canada geese involved were from a migratory, rather than resident, population. This knowledge is essential for wildlife professionals to develop policies and techniques that will reduce the risk of future collisions. The team’s findings were published in the journal “Frontiers in Ecology and the Environment” in June.

Photo: A crane lifts US Airways Flight 1549 from the Hudson River in lower Manhattan on Jan. 17, 2009. Two days earlier it had crash-landed in the river after colliding with a flock of geese.

The US Airways plane took off from New York’s LaGuardia Airport, colliding with a flock of geese approximately 2,900 feet above the ground, extensively damaging both engines five miles from the airport. The pilot conducted an emergency landing in the Hudson River, and all 155 people on board survived with only a few serious injuries. Investigators at the National Transportation Safety Board later sent feathers and tissue extracted from the plane’s engines to the Smithsonian in Washington, D.C., for analysis.

Researchers in the Feather Identification Laboratory at the Smithsonian’s National Museum of Natural History used molecular genetic techniques and feather samples from museum collections, as well as a technique developed for rapid species identification with small genetic samples called DNA barcoding, to determine that the birds involved were Canada geese (Branta canadensis). This is one of the largest species of birds in North America. The birds involved are estimated to have weighed about 8 pounds each.

Photo: An investigator from the National Transportation Saftey Board removes bird remains from one of the jet engines of US Airways Flight 1549. The remains, analyzed by Smithsonain scientists, were determined to be from migratory Canada geese from the Labrador region. (Photos courtesy NTSB)

The next step for the scientists was to find out if these geese were migratory or non-migratory (resident) birds. “Determining whether these birds were migratory or not was critical to our research and will help inform future methods of reducing bird strikes,” says Peter Marra, research scientist at the Smithsonian’s Migratory Bird Center located at the National Zoological Park, and lead author of the project’s paper. “Resident birds near airports may be managed by population reduction, habitat modification, harassment or removal, but migratory populations require more elaborate techniques in order to monitor bird movements.”

The team took their research to a molecular level at the Smithsonian’s Museum Conservation Institute labs in Suitland, Md., where experts examined stable-hydrogen isotopes from the feathers to confirm whether the geese were from resident or migratory populations. Stable-hydrogen isotope values in feathers can serve as geographic markers since they reflect the types of vegetation in the bird’s diet at the time it grew new feathers after molting. Using a mass spectrometer, which measures the masses and relative concentrations of atoms and molecules at high precision, Museum Conservation Institute scientists compared the bird-strike feather samples with samples from migratory Canada geese and from resident geese close to LaGuardia Airport. Their analysis revealed that the isotope values of the geese involved in the crash of Flight 1549 were most similar to migratory Canada geese from the Labrador region and significantly different from feathers collected from Canada geese living in the New York City region.

“Knowing the frequency and timing of collisions is important,” Marra says. “Otherwise we are missing valuable information that could reveal patterns of frequency, location and the species involved.”