By Michael Kernan
Smithsonian magazine, March 1996
Taken from: http://www.smithsonianmag.com/arts-culture/atm-199603.html
Around the Mall & Beyond
Protecting museum treasures – paintings by the masters, antique furniture, the delicate wings of a tropical beetle – requires the strictest climate control, right? Maybe not, say these scientists
“We could save up to $400,000 on the electric bill for this building alone. Every year.” That’s what the man said.
I better get this right up top: I’m writing about some Smithsonian scientists who have shown that museums and galleries are spending far too much money on climate control. Photographs, old planes, bones, rare bugs and what have you are much tougher than we thought.
That’s the short version. It was not easy to come by. I had no trouble finding the Conservation Analytical Laboratory Research Group at the Smithsonian’s sprawling Museum Support Center at Suitland, Maryland, but the scientists themselves were another story. They spoke a language of numbers, acronyms, graphs and formulas that made me yearn for the simplicity of E=mc2. Slowly I began to make out what they were telling me.
“Until a few years ago, people didn’t know precisely how much objects are affected by fluctuations in relative humidity and temperature,” explained Charles Tumosa, “but they knew that existing air-conditioning systems could maintain humidity at 50 percent, plus or minus 5 percent. So they felt that was what it should be, and if plus or minus 5 percent was good, plus or minus 2 percent was better.” Believing only that too much fluctuation in the atmosphere was bad, museums and galleries concentrated on reducing that tiny plus-or-minus factor.
“As sensor and HVAC (heating, ventilation and air-conditioning) systems got better, they tightened and tightened their specifications, going for that utopian 0 percent. To do anything less would be morally reprehensible. They could spare no expense.”
Museum professionals had observed that huge changes in air conditions cause damage; but it wasn’t known if small changes over a long period do, too. In the 1970s, administrators at the National Gallery of Art in London, going by certain experiments on wood and recalling their wartime experience when paintings were stored in a cave without damage, set a conservative (if not entirely arbitrary) standard of 55 percent relative humidity for the building.
This standard was designed to accommodate all sorts of substances, with major exceptions such as metal, which corrodes, papers containing acids, and cellulose acetate film base, which breaks down. In other words, at that time museums knew that extreme conditions damage materials, but they did not know how much, or when. So they overcompensated.
This is where the Smithsonian’s lab came in. Marion Mecklenburg, for 20 years an art conservator, got a doctorate in engineering just so he could explore this field. He has put together a remarkable team to try to determine exactly how the environment does affect objects. Mark McCormick-Goodhart, a renowned photographic scientist, holds many patents from his years in industry; PhD chemist David Erhardt comes out of an advanced math background, as do Mecklenburg and Tumosa, a PhD chemist who did forensics for 18 years with the Philadelphia police before coming to the Smithsonian.
“Let’s look at the physical and mechanical problem of relative humidity and temperature fluctuations,” said Mecklenburg in his brisk way. “No serious work had been done on this. We were the first.”
Different materials, different problems. Oil paints, acrylics and other painting media can be damaged by extreme cold, Mecklenburg explained, but they are not especially vulnerable to moisture.
What? I’ve never heard that. I thought paintings were delicate, I said.
“Well,” replied Mecklenburg, “when I was a painting conservator I always wondered why the works from Holland were often in better shape than the ones from Italy. I found out that paint does not respond much to moisture changes. But the Dutch panels tend to have less gesso (a coating applied before painting) than the Italian ones. That gesso is the weak link. It doesn’t easily expand and contract in response to large changes in the environment.”
Speculating that perhaps things aren’t necessarily ruined by slight expansion and contraction, that perhaps they need not be “restrained” in an atmospheric straitjacket, so to speak, the team has been measuring the stresses that many materials — bones, mineral specimens, aircraft surfaces, marine paint, beetle wings and so on — endure before they finally undergo plastic deformation and actually split.
Mecklenburg: “The question then is whether you can directly relate environmental factors to the basic mechanical problems of materials. The answer is: absolutely. We have developed completely new thermodynamic models that show the exact relationship of temperatures and relative humidity to the mechanical properties of materials.”
What’s more, the findings have been computerized, producing analytical models for all sorts of materials, enabling Mecklenburg and his team to literally predict the splitting point of, say, yak leather. Armed with exact knowledge of the safety margins, museums no longer have to overcorrect. The difference in costs is staggering.
“The energy cost of this building alone is $1.2 million a year,” noted Mecklenburg. “Each little room has its own micro-HVAC system. The newer buildings have insulation to prevent condensation on the walls. The older ones don’t. In the old Arts and Industries Building, moisture condenses between the ceiling and the roof, and in the summer it actually rains in there.”
Dehumidifiers in summer and humidifiers in winter are the answer, but in any large building the cost of bringing the fluctuations below 5 percent is tremendous. The National Museum of Natural History spends $1.2 million a year on controlling its environment; if it were to try to follow conventional museum standards, the cost would double.
The current specifications for the future National Air and Space Museum annex at Dulles Airport call for 43 percent relative humidity with a margin for error of plus or minus 2 percent. “That’s a hangar!” Mecklenburg exclaimed. “You’ll never get that kind of control. The energy costs would be ridiculous. If they heed our recommendations, that annex could save $45 million over 30 years in its electric bill.”
The National Gallery of Art already saves $100,000 a year because it has relaxed the allowable fluctuations in just one part of the building by a mere 2 percent.
The word is out. So far, at least 80 museums and exhibit organizations from all over the world have requested information on the team’s new approach, and some have already reported huge savings. So the lab team is saying tighter controls are not necessary. And I’m asking how they know this.
I began to find out when I saw the lab itself. Scattered all around are little Plexiglas boxes, 36 of them, tiny torture chambers full of dials and wires and clamps. Inside are temperature gauges and enough silica gel to control the relative humidity.
A thick strip of, say, rabbit skin glue, often used in art construction, is set between pincers that want to pull it apart lengthwise. For two years it is stretched, bit by bit, until it is elongated by 4 percent, at which point, the team discovered, it will break.
The lab team has found that changes as great as plus or minus 15 percent relative humidity will cause stretching of only 0.4 percent, a mere one-tenth of the actual breaking point. This and numerous tests of other materials are showing that it is overkill for museums to worry about minuscule variations in the atmosphere.
Inside the boxes are little gauges and other devices to test the all-but-invisible changes in materials. I saw tests on whalebone, epoxy glue, egg tempera paint, whale teeth, aircraft paint, various woods and a waterbug’s shell. The lab has hundreds of paint samples, some dating back nearly 20 years and saved up by Mecklenburg for just such a purpose.
Though most of the work concerns long-term change, the team has also discovered things about short-term changes, such as vibration and shock, as when a careless forklift operator drops a Da Vinci portrait. “We’re learning how to pack things more efficiently in terms of their fragility,” he noted. “For instance, the vibration from trucks isn’t as bad as we had thought.”
He showed me some graphs that David Erhardt has been working up, defining a correlation between chemical degradation and physical behavior. Then he treated me to some serious formulas that have emerged from all this experimentation, formulas that predict the elastic behavior of any material in various physical conditions.
“Our research has many important applications in the non-museum world. We could tell, for example, if there’s going to be a strain on the walls of a nuclear reactor when it is flushed with cold water during an emergency. We can predict stresses on airplanes. Up to now, planes made from composites have probably been overdesigned. If you don’t know the exact dangers, you overdesign.”
Naturally, with the prospect of gigantic savings in building and maintenance, industry has taken notice of the team’s work. And the team has recently joined forces with the University of Maryland to submit a proposal for a National Science Foundation grant.
Recommendations by Mecklenburg and Tumosa for atmospheric control parameters in all the Smithsonian Institution buildings are currently under study, and it looks likely that savings of $2 million a year will be possible. So now no one is sneering at those quiet guys down the hall who seemed to be just fiddling around stretching paint.