If you've tried listening to any of your old CDs lately, if you even own them anymore, you may have noticed they won't play. That's what happened to mine, anyway.
CD players have long since given up on most of the burned mixes I made in college. (In some cases, this is for the best.) And while most of the studio-manufactured albums I bought still play, there's really no telling how much longer they will. My once-treasured CD collection—so carefully assembled over the course of about a decade beginning in 1994—isn't just aging; it's dying. And so is yours.
"All of the modern formats weren't really made to last a long period of time," said Fenella France, chief of preservation research and testing at the Library of Congress. "They were really more developed for mass production."
France and her colleagues are trying to figure out how CDs age so that we can better understand how to save them. This is a tricky business, in large part because manufacturers have changed their processes over the years but won't say how. And so: we know a CD's basic composition—there's a plastic polycarbonate layer, a metal reflective layer with all the data in it, and then the coating on top—but it's impossible to tell just from looking at a disc how it will age.
"We're trying to predict, in terms of collections, which of the types of CDs are the discs most at risk," France said. "The problem is, different manufacturers have different formulations so it's quite complex in trying to figure out what exactly is happening because they've changed the formulation along the way and it's proprietary information."
Even CDs made by the same company in the same year and wrapped in identical packaging might have totally different lifespans. That's what Library of Congress researchers found when they tested twin copies of Paul Winter's Grammy-nominated 1987 album Earthbeat.
The two seemingly identical discs were exposed to extreme heat and humidity in an accelerated-aging machine. They cooked for about 500 hours at 175 degrees and in relative humidity of 70 percent—about what you'd expect on a sweltering July day in New York City, but not quite as humid as a rain forest. One of the CDs emerged relatively unscathed. The other was zapped of its musical data, completely destroyed by oxidation. You can see the ruined CD, which became almost totally transparent, on the right:
"They started out looking exactly the same," France said. "I wish we could definitively say, you know, 'If you have a CD that was manufactured in 1984, that's terrible.' But it's not quite that simple."
If you're willing to part with your old CDs, the library will happily destroy them for you. "In the name of science!" France says. "And just so people know that no library materials are harmed." (Update: A spokeswoman with the Library of Congress asked me to let people know that the center now has a "sufficient supply of CDs for its research and testing.")
The Center for the Library's Analytical Science Samples is a laboratory for destruction, a place where researchers can practice "destructive testing" on non-library materials as a way to learn how best to care for actual library collections. Staffers at the center might opt for more destructive aging tests, like the treatment that Earthbeat suffered, or just let discs age naturally and check in on them every decade or so.
There are all kinds of forces that accelerate CD aging in real time. Eventually, many discs show signs of edge rot, which happens as oxygen seeps through a disc's layers. Some CDs begin a deterioration process called bronzing, which is corrosion that worsens with exposure to various pollutants. The lasers in devices used to burn or even play a CD can also affect its longevity.