It's probably the best-known engineering problem — and most stations do nothing about it: the limited life span of videotape.

Until recently, only major networks and studios could justify the time and expense of backing up old content or storing the originals off site. But the explosion of licensed video sites and the fast-growing market for documentary footage have created new opportunities for stations to monetize old footage. That is, for stations who can locate and transfer their footage on demand.

But when it comes to videotape, age both giveth and taketh away. By the time old footage achieves nostalgic and historic market value, it has probably suffered physical deterioration. Too often, potential profits have already evaporated. Or more accurately, flaked away.

"Magnetic recording tape was never designed as a long-term storage medium," says Peter Brothers, founder of SPECS BROS, a magnetic tape restoration facility in Lodi, N.J.

"Most tapes have not been stored properly," says Brothers. "Just like any other material, video tape decays when exposed to harmful environments."

Unfortunately, that describes any environment that includes heat or cold, which expand or contract the tape, causing gradual stretching and structural damage. An even worse culprit is humidity.

"Moisture causes a chemical reaction called binder hydrolysis, which breaks down molecules in the recording and backing layers of the tape. This leaves a sticky residue, which can foul tape machine play heads or physically jam altogether during playback," says Brothers.

Brothers ought to know. He's been studying the problem for 25 years and helped establish industry standards for tape preservation and restoration for SMPTE, the American National Standards Institute and others.

Videotape fares best in cool temperatures at 30 percent humidity, which occurs naturally in underground salt mines, such as those maintained by Iron Mountain. But even under ideal conditions, tapes begin to deteriorate after 20 to 25 years.

"Each tape format presents its own challenges for how it decays over time," says Doug Warner, the Director of Engineering for the Paley Center for Media (formerly the Museum of TV & Radio) which maintains in-house equipment to play back most major videotape formats, including two-inch quad, one inch, and all videocassette formats.

"The majority of our collection came in as 3/4-inch sub-masters," says Warner. And because the 3/4-inch U-Matic tape format is nearly 40 years old, Warner's staff has been working for years to create digital backups of the collection, an ongoing task that might literally never end.

Of course, to be duplicated a tape must first be playable. And tapes over 30 years old very often require physical restoration. That's the focus of Video Interchange, the company Bob Pooler launched in 2002 in Waldoboro, Maine, where Pooler lovingly maintains a dizzying assortment of fading or defunct magnetic media players.

A lifetime of broadcast engineering experience plus more recent trial and error has made Bob Pooler a master of tape restoration. Among his favorite techniques is tape baking, the craft of baking magnetic tape to stabilize its layers long enough for one safe ride past the play heads.

Brothers helped to invent and perfect tape baking and other restorative methods described on his Web site. Although Pooler and Brothers have never met, they agree that repairing mere moisture damage is the easy part.

In addition to a wide range of domestic accidents, including countless dog-chewed cassettes and toddlers armed with lethal jelly sandwiches, Pooler's greatest challenge was restoring tapes damaged in during Katrina flooding.

"Most of the tapes were exposed to nearly every known contaminant, including some disgusting ones. For our own health and safety, we had to disinfect the tapes without compromising the binder layer."

"Sewage is no fun," agrees Brothers who likewise considers Katrina damage his major challenge, alongside the restoration of videos damaged during military action, the nature of which he's not at liberty to discuss.

Because a "restored" master tape remains highly fragile, that first playback is usually the only one. It's routinely double-recorded for safety's sake.

"The new digital technology could not have come at a better time," says Bob Pooler. "Previously, we could only back up tapes analog to analog. And every tape generation meant an additional loss of quality."

Whatever new technologies lie ahead, says Pooler, "we'll be able to make lossless transfers to the new media, say, every 30 years or so."

Peter Brothers agrees, but notes that the arrival of digital technology presents new problems. "For over 20 years, two-inch analog tape was the only standard, so the biggest challenge was keeping the old machines in working order. But there's no clear consensus in digital. So it's not just the machines that become obsolete, but also a wide range of underlying technology such as codecs and other software."

There's also the matter of destination storage media. Although Pooler has restored and copied entire archives for professional clients, he says that the bulk of his business is "vintage family video and audio." His clients are satisfied to receive ordinary DVDs, which are estimated to last for up to 80 years.

DVDs won't work for broadcasters, says the Paley Center's Warner. "Consumer DVDs only hold 4.7 gigabytes of data, so the video must be highly compressed. Our files are stored uncompressed for maximum quality. Most of them take at least 80 gigabytes."

In addition to Paley Center hard drives, the backup medium of choice is Sony's Digi-Beta tape. The same goes for SPECS BROS, which counts the Paley Center among its frequent clients for restoration services.

"Properly stored, Digi-Beta tapes should be good for 20-25 years," says Peter Brothers.

Despite the industry migration to digital, a surprising number of professional clients continue to request analog playback, most often on Sony's Beta SP or consumer Mini DV.

Both Brothers and Pooler are old enough to at least think about retirement. And both are worried that when they do, their expertise will leave the industry with them.

"It took me decades to acquire the necessary skills," says Pooler, whose services are booked weeks in advance. I hardly have time to teach anyone how to use a scope and nobody is teaching vacuum tube theory. Maintaining this old equipment will soon be a lost art."

Brothers is only a little more optimistic. "I do what I can. I've taught seminars on restoration and preservation for the Smithsonian and even NASA. There are schools, like NYU, which teach media preservation, but there really is no training in physical restoration."

"But the good news is that once you transfer from analog to digital, the hard part is done," adds Brothers. "The digital file contains all the metadata for a perfect transfer so future transfers can be done automatically."

Tech Spotlight, by TVNewsday Contributing Editor Arthur Greenwald and commercial producer-director  Glenn Przyborski tackles engineering issues every Thursday in TVNewsday. Do you have a technical or engineering question you'd like to see answered? Send it to greenwald@tvnewsday.com.