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Oberlin College researcher helps fight corrosion in historic pipe organs

Started by KB7DQH, March 10, 2013, 09:01:16 PM

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This is likely the best article of its type to show up in the mainstream press, published on the WWW, and found by the Google webcrawler...

QuoteThe pipe organ is the most humanlike of musical instruments.

With a great whoosh of breath from the leathery lungs of its bellows (or, as technology has improved, from steam engines, and finally electric blowers), the organ fills its towering pipes with air. The sounds spilling from that choir of metallic throats can be anything from the pew-rattling thunderclap of a bass chord to a nightingale's high, delicate trill.

Perhaps it's no surprise, then, that these prodigious artists can develop life-threatening cases of throat cancer.

The pipes in some of the world's most historic organs are rotting. Aggressive corrosion is gnawing away at the centuries-old lead and tin larynxes that give the instruments their distinctive voices, causing the pipes to flake, fracture and eventually collapse. More-modern organs aren't immune, either.

Oberlin College chemistry professor and avid organist Catherine Oertel is part of an international research effort to confront the corrosion threat. Using sophisticated diagnostic tools, including X-rays and ion beams that probe the atomic structure of the decay, the small band of scientists has fingered an unexpected culprit for the damage. As in an autoimmune disease, the organs are attacking themselves.

"It's a very complex environment because of all the metal and wood," Oertel said, "and the interaction between the two is the problem."

The research, which is ongoing, is suggesting solutions that may spare further harm to these irreplaceable artifacts.

Funny-sounding pipes raise the alarm

In the early 1990s, the organist at 'St. Jakobi Church in Lubeck, Germany, began noticing problems with the parish's renowned organ.

"Some of the pipes started to sound funny," said Carl Johan Bergsten, a research engineer at Sweden's University of Gothenburg Organ Art Center who's also a church organist. "He could hear something going on because the pipes were out of tune."
Graphic.jpg View full size 

The oldest pipes in the organ were incorporated from an earlier, Gothic instrument constructed in 1467. The remainder were installed when master German organ-builder Friedrich Stellwagen enlarged the church's organ in 1636.

Inspection of the out-of-tune pipes revealed extensive, powdery white corrosion inside their lowest part, called the foot. The pipe feet rest in channels atop the organ's airtight wooden "wind chest." The pipes protrude from the chest like straws poking through a soft-drink top.

Normally, when the organist presses a key, air flows from the wind chest into a pipe, where it creates a musical tone either by passing over a whistlelike slot or vibrating a metal reed. But corrosion had riddled the Stellwagen organ's pipes with cracks and holes. Air leaks and the resultant pressure drop inside the pipes caused them to fall out of tune.

Europe's churches and concert halls are home to most of the world's oldest surviving pipe organs -- as many as 20,000, according to estimates. They date as far back as the Renaissance and Baroque periods, when organs consisting of hundreds or thousands of soaring pipes, encased in elaborately carved and gilded wooden cabinets, were constructed as awe-inspiring centerpieces of the continent's cathedrals. For their time, they were among the most complex machines to be built.

European composers such as Bach, Handel and Mozart wrote some of their most memorable pieces for pipe organ. The instruments remaining from that time are a cherished part of European cultural heritage. America's considerably younger historic organs replicate European design and craftsmanship.

(Ancient Greece claims the honor of inventing the instrument in the second century B.C. -- a water-driven device called the hydraulis that provided entertainment in palaces, coliseums and public festivals.)

Research project looks to determine cause

After the discovery of the Stellwagen corrosion, checks of other historic European organs showed similar damage. In some cases, the only option was to replace the pipes with modern ones, which altered the organ's sound, diminished its pedigree and reduced its links with the past. "All these incremental changes take away from what was heard and composed for by historic composers," Oertel said.
stellwagen.jpg View full size The historic Stellwagen organ in Lubeck, Germany's, St. Jakobi Church helped alert researchers to the problem of pipe corrosion. Courtesy of Catherine Oertel 

Facing an apparent corrosion epidemic, the governing European Commission in 2003 authorized a research project called COLLAPSE -- for Corrosion Of Lead and Lead-tin Alloys of organ PipeS in Europe -- to figure out what was going on. Bergsten, who'd spent much of his career at the Swedish automaker Volvo, coordinated the effort, which involved scientists from three Swedish and Italian universities, a Danish organ manufacturer and the St. Jakobi parish.

Oberlin's Oertel wasn't a formal COLLAPSE partner but collaborated with some of its Swedish researchers, as well as conducting her own studies funded by the National Science Foundation while a postdoctoral student at Cornell University and later as an Oberlin faculty member.

Oertel had played piano as a child and took up the organ while majoring in chemistry at Oberlin. The highly regarded liberal-arts college is well-stocked with pipe organs, including three large ones used for performances and about a dozen more for practice sessions. (They're all corrosion-free.)

Oberlin's science faculty often does music-related research. Studying organ pipe corrosion was "a really exciting way to merge these two interests of mine," Oertel said.

Need for frequent repairs dates to the 16th century

Finding the corrosion's cause was the scientists' first priority; that would dictate the strategies to preserve the decaying organ pipes. The COLLAPSE researchers launched comparison studies of affected and corrosion-free organs in Italy, Belgium, Germany and the Netherlands. They collected and analyzed bits of corroded pipe, sampled the air in and around the instruments, and tracked temperature and humidity readings for a year.

At first, the researchers suspected some relatively recent, modern phenomenon -- maybe industrial or agricultural air pollutants, or upgraded church ventilation systems -- was to blame for the corrosion. After all, the pipes had seemed fine for hundreds of years, only to be felled lately.
stellwagen interior.jpg View full size An interior view of the Stellwagen organ shows the variety of the instrument's pipes. The base of each pipe rests atop a wood wind chest, potentially allowing acidic funes from the wood to enter the pipes and cause corrosion. Courtesy of Catherine Oertel 

But a check of old literature found accounts of frequent organ pipe repairs, especially in Germany, as far back as the 16th and 17th centuries, Bergsten said. (Apparently, there was less concern at the time about altering what were not yet historic instruments.) German texts called the damage "bleifras," which translated as "lead-eaten."

The corrosion's location turned out to be an important clue. It began at the bottom of the vertical pipes. And, significantly, it started on the inside, not the exterior. If the corrosion's origin was external, as an enveloping cloud of pollution would be, the decay should first appear on the pipes' skin, progress inward and extend all along the pipes' length.

"We quite soon realized the source of this problem is coming from inside the organ," Bergsten said.
SEM corrosion.JPG View full size Under extreme magnification using a scanning electron microscope, the components of corrosion forming on a sample of lead-tin alloy look like a forest of treetops. Courtesy of Catherine Oertel 

What's inside an organ? Wood, mainly. And wood, especially oak and walnut, is known to be corrosive to lead. The gradual breakdown of wood's cell walls releases tiny wisps of acetic acid. Curators at the British Museum had seen historic lead coins and seals begin to crumble while stored in wooden cases.

Constructed of oak and airtight by necessity, pipe organs' wind chests are an ideal place for acetic acid to build up. The pipes' feet are constantly in contact with the acid vapors. Firing up the organ's blower and pressing its keys to play inadvertently injects acid fumes higher into the pipes. Eventually, the metal rots.

Some pipes have managed to withstand centuries of exposure unharmed, for reasons that aren't clear. Over time, as the organ wood ages, its acid output should diminish. But when organ builders refurbish an instrument with a new wind chest, the fresh wood revives the emission process.

Worse, the white glue that's been used since the 1960s to strengthen joints and seal wind boxes also emits acetic acid. That combination of new wood and glue may help explain the recent wave of pipe failures in ancient organs, as well as corrosion in modern ones. "We have a quite strong correlation between these problems and restoration and repairs 10, 20, 30 years ago, where new wood was introduced into the organ," Bergsten said.

Lead-tin samples prompt discovery

Renaissance-era organ builders didn't have many options when it came to pipe material. Gold and silver were too expensive. Iron was too hard to allow the hand-rolling and incremental re-adjustments that produce the proper pitch and timbre. Copper and brass produced too resonant a sound.

Lead, and alloys of lead and tin, struck the right combination of malleability and tone.

The COLLAPSE project focused on pure lead organ pipes, which clearly were highly vulnerable to corrosion. But some researchers believed that lead pipes containing tin additives gained some protection. Oertel set out to test the tin concept, working with fellow scientists at Cornell and Sweden's Chalmers University of Technology.
chamber1.jpg View full size Inside a sealed laboratory chamber, researchers expose samples of the metal used in organ pipes to acid vapor under varying environmental conditions. Courtesy of Catherine Oertel 

In glass canisters, the researchers placed stamp-size samples of lead alloyed with as much as 15 percent tin. They pumped in acetic acid fumes and let the samples sit as long as a month. The humidity in some of the canisters was set at a comfortable 60 percent, comparable to a modern, climate-controlled church. Other canisters were a tropical 95 percent.

At low humidity, the lead-tin samples showed dramatically less corrosion than pure lead ones, confirming that tin had some protective influence. But the lead-tin squares exposed to high humidity were covered with cauliflowerlike crusts of corrosion.

Oertel and her colleagues used a tightly focused ion beam to cross-section the corrosion layer without destroying it, as a normal cutting tool would. A powerful scanning electron microscope and X-ray analysis identified the corrosion's components. The presence of tin particles in the debris showed that its protective ability was swamped in high-moisture conditions.
Copy of DSCN0140.JPG View full size Catherine Oertel, center, and Oberlin College organ perfornance majors Nick Capozzoli and Katelyn Emerson stand in front of the pipe organ at Peace Community Church. Oberlin students practice on the organ, which was built in 1984 in the style of 18th Century the German organ builder Gottfried Silbermann. John Mangels, The Plain Dealer 

That's important to know, since organ caretakers sometimes use humidifiers to keep the instrument's wood from drying and cracking, Oertel said. Without careful monitoring, the heightened humidity could spur aggressive corrosion, even in pipes that were thought to be immune.

Other protective strategies include avoiding the use of oak and white glue when doing refurbishment and installing ventilation fans -- as has been done with the Stellwagen organ in Lubeck -- that can prevent the buildup of acid fumes in organs' wind chests.

Some of the Swedish and Italian researchers are experimenting with coatings made of tiny nano-particles that can be applied to the wood in an organ to neutralize acid before it can reach the pipes. Bergsten and his colleagues are developing sensors that can be installed in organ pipes to detect acid emissions and other harmful conditions.

Oertel is continuing her corrosion research, looking at other combinations of metals that are at risk. "There are pipes that have 90 to almost 100 percent tin, and some of those are suffering from corrosion," she said. The pipes in a historic French organ in Bordeaux, for example, are "virtually pure tin, and you can see they're suffering from some holes. So there's a lot more of the composition [questions] for us to explore."

Last summer, the Ohio scientist was in Germany and had a chance to play the ancient Stellwagen organ. "That was a really special experience," she said. "It's an instrument that's been part of the life of the church for so long, and it's been played by people who are contemporaries of [German composer Dieterich] Buxtehude and Bach.

"In Germany in the 1600s and 1700s, there would have been hundreds of organs like this," in almost every church and village, Oertel said. Now, "these organs are the endangered species of the musical world." Helping save them "is a deeply satisfying project."

The objective is to reach human immortality—that is, to create things which are necessary to mankind, necessary to the purpose of the existence of mankind, and which have become the fruit that drives the creation of a higher state of mankind than ever existed before."