They were supposed to last for 100 years. They were supposed to become family heirlooms, allowing home movies and pictures to literally defy time and keep memories as fresh as the day they were made.
But the compact disc, as it turns out, may not exactly last forever. In fact, some CDs undergo “CD rot,” the slow, gradual destruction of the data they contain.
In manufactured CDs, the “rot” is characterized by pin-prick holes in the silver, or a clouding and darkening of the silver surface which results in garbled data. On burned writable and re-writable CDs the problem is often invisible but has the same effects, according to Sam Crow, a technical assistant in the EMU Computer Lab.
“The manufactured CDs corrode over time and the discs won’t be able to be read,” Crow said. “For burned CDs, the dye corrodes due to light exposure and due to just age.”
Colin Kelly, aerial map coordinator in Knight Library’s government documents section, said CDs may not be a reliable storage format.
“I don’t consider CDs a viable long-term archive system, and I don’t think anyone should,” Kelly said. “Most of our valuable digitized images we keep on hard drive, and if I do use (CDs), it would not be for more than five years at most.”
Kelly handles large images, documents and series of photo-maps. Rather than use CDs, Kelly said that when he can’t put the largest series on hard drive he uses the “mass storage unit,” a massive hard drive for library archives.
Raenie Kane buys and sells used CDs for The House of Records, a music store located at 258 E. 13th Ave. in Eugene. Kane said she had never heard of the CD rot phenomenon, but identified the symptoms of CD rot as commonplace in the CDs customers try to sell to the store.
“In the 13 years I’ve been buying and selling CDs, I’ve never seen holes in the surface of the silver,” Kane said. “I’ve seen the clouding though, but I’ve always attributed that to a manufacturers defect, not age, but it certainly ruins the CD.”
The structure of a CD is essentially a data sandwich. A data-carrying layer is placed between a layer of plastic on the bottom and lacquer and a label on the top, according to Kane. In manufactured CDs, the data carrying layer is a slice of aluminum, while in writable CDs made for use with a home CD burner, the data layer is made up of a dye that is modified by the burners.
Jerry Hartke, who runs Media Sciences, Inc., a Marlborough, Mass. laboratory that tests CDs, said if the manufacturer applied the lacquer improperly, air can penetrate and oxidize the aluminum, eating it up much like iron rusts in air, according to a May 6 article from The Associated Press. Factors such as temperature fluctuations can also weaken the discs’ structure causing the layers to pull apart.
Burned writable CDs may have an even shorter lifespan according to PC-Active, a Dutch personal computer magazine. In a study of different CD-R brands published in August 2003, results showed CD-Rs are unreadable in as little as two years because the dyes in the CDs’ recording layer fade.
When the CD is made on a home burner, the writing laser “burns” the dye, which becomes dark, to represent a “1” while a “0” is left blank. If the dye fades, the reading laser perceives an entirely empty disc of zeros.
CD rot is not likely to be a big problem for users who take care of their CDs, according to Hartke. It’s more common that discs are rendered unreadable by poor handling.
“If people treat these discs rather harshly, or stack them, or allow them to rub against each other, this very fragile protective layer can be disturbed, allowing the atmosphere to interact with that aluminum,” he said.
Tyrone Dion works at the CD/Game Exchange in Eugene, which buys and sells secondhand music. He said most people aren’t careful with their CDs.
“You know, I just chuck my CDs into a big old pile and they get all scratched so they don’t live long enough to experience the effects of deterioration,” Dion said. “We see a lot more of the media deterioration like scratches and mishandling than we see the actual deterioration of the (data).”
Kane said she also gets mishandled CDs.
“People are trying to sell us all sorts of stuff,” she said. “People are trying to give us the dredge of their collections, so their CDs are not usually in the best shape.”