Boston College researchers have found a way to store about 19 times more data on a disk than a common DVD can hold, using optical media made with common products, the December issue of Nature Materials reports. An epoxy glue sold at hardware stores and a glass-like substance were formed into a DVD-size disk able to hold about 87 gigabytes, equal to 87,000 paperback books. A typical DVD holds about 4.7 gigabytes. The discovery is unique because the materials remained stable, keeping data intact, the project's leader said. Companies including International Business Machines Corp. are exploring ways to increase computer data-storage capacity, while reducing costs and size in devices ranging from desktop personal computers to massive machines able to hold the contents of the U.S. Library of Congress. Optical storage holds less data than a magnetic hard-disk drive yet is more stable and rugged.

"This all began when we were trying to do something completely different with the materials," said John Fourkas, a chemistry professor who led the research at Boston College's Eugene F. Merkert Chemistry Center. "It was by accident."

The researchers used a laser set at a specific intensity and focal range to write information digitally in layers by causing a chemical change in the material.

When the same laser was set at a lower intensity and fired at the same area, the material gave off a fluorescent glow indicating readable data was present. Lasers used on standard DVDs and compact discs read pits either engraved on the surface by another laser or stamped in mass production.

With the Fourkas-led team's discovery, in the area known as 3D optical-data storage, the changed material is transparent when not hit directly by the lower-intensity laser. That lets the laser focus on different levels in the material to write and read digital data, Fourkas said. So, far, researchers have been able to write data on as many as 25 levels, he said in an interview.

"We don't yet know how this happens, exactly," Fourkas said.

The materials that the team used are stable, and the data don't degrade after repeated readings by the low-intensity laser.

The discovery began about three years ago, Fourkas said, when fellow researchers Christopher Olson and Michael Previte saw that some materials emitted light, or fluoresced, when hit by a laser beam.

"We thought it might be useful for something," Fourkas said. Specific research on the phenomenon began about a year and half ago, funded by a $344,000 grant from the U.S. Air Force, Fourkas said.

"The Air Force is interested in having stable memory devices capable of storing large amounts of data in a small device in satellites and airplanes," he said.

Olson, currently a graduate student in Fourkas' laboratory, and Previte, now a postdoctoral fellow at the Massachusetts Institute of Technology, co-authored with Fourkas the Nature Materials report: "Efficient and Robust Multiphoton Data Storage in Molecular Glasses and Highly Crosslinked Polymers."

The researchers have applied for a patent, Fourkas said. They haven't been in contact with any companies about the discovery.

A number of issues still need to be worked out, Fourkas said. One is that once data is written to the disk, it can't be changed. Each disk has to be written individually, he said. A mass- production method would need to be found to lower costs.

The cost of the laser also is prohibitive.

"The one we use is about $100,000," Fourkas said. The cost would come down with mass production, he said.