Talk about your vanity mirrors. The nearly completed Large Binocular Telescope (LBT) on Mt. Graham in Arizona will have not one, but two of the largest one-piece telescope mirrors in the world.

For telescopes, size really matters. Not in terms of length, but in terms of the diameter or "aperture" of the light-gathering optics. The weight of large lenses can distort them, however, ruining the view of the heavens. That's why the big boys of astronomical gazing use curved mirrors.

Yet even mirrors can only be made so big before they start to bend. The current record-holder, the twin W.M. Keck telescopes in Hawaii, combines clusters of 36 honeycomb-shaped smaller mirrors to achieve apertures of 30 feet (10 meters) for both instruments.

"It certainly will be the worlds largest telescope, and it's been a long, long project," said physicist Bruce Atwood of Ohio State University. Atwood's expertise is in building big telescopes, and he has led the research in perfecting the special process that will complete the LBT's mirrors.

While the large glass disks that will form the mirrors have been constructed and are in the process of being polished, the process of applying their reflective coating of aluminum still waits. That's where Atwood's team comes in.

The final aluminization will have to be done on-site, atop Arizona's Mt. Graham, more than 10,000 feet above sea level. If applied at a lower altitude, the ultra-thin coating would distort while being carted up the mountain. So when all the bugs have been ironed out, the entire system will have to be shipped to Arizona to meet up with the mirrors in their new mountain home. Then Atwood's aluminization "kit" will be reassembled and used to apply the final coatings, completing the mirrors.

It is a much touchier process than simply splashing the back of the mirror glass with some liquid aluminum, so the OSU team has devised a way of laying it on as aluminum gas. A dry run is planned for this month.

"We will actually simulate the mirror," explains Atwood. "We may build a full-sized dummy mirror out of aluminum. But it won't be something that's very reflective."

Basically coating the mirrors will work like this: A mirror's support backing, or "cell" will be sealed to a domed "bell jar" vacuum chamber. Combined, the apparatus will look like an enormous iron hamburger.

Then, powerful pumps will do their darndest to suck air out of the chamber, up to about 99.9 percent, creating what Atwood termed a "low vacuum." Still, that's nowhere near empty enough.

To create a "high vacuum," which will remove another 99.9 percent of the remaining air molecules, a special cryopump system needs to be completed.

While a high vacuum is still not as empty as the hard vacuum of outer space, Atwood says that at such low pressure each lonely remaining molecule of air will have about a yard of elbow room to bounce around in. Only then will it be safe for the cloud of vaporized aluminum to cross over and settle onto the cell.

There's still a problem with air is that: Like flies stuck to a freshly-painted wall, just a few too many molecules of oxygen would ruin the mirror's finish, not by creating lumps however, but by chemically reacting with the aluminum.

"Then you would have aluminum oxide snow," explains Atwood.

So, to avoid accidentally creating a matched set of 28-foot snow globe paperweights atop a mountain, Atwood's team is carefully checking each stage of the process.

"We're building the high-vacuum system," he says. "We've tested all of that at low-vacuum."

"Vacuum is kind of like golf scores," Atwood jibes. "Lower numbers are better."

But in telescopes, bigger numbers rule. "There have been three successful technologies for developing large telescopes," says Atwood. "A meniscus monolithic mirror is relatively thin. They are uniform cross sections, and have lots and lots of support."

Secondly, there are segmented mirrors, like the Kecks in Hawaii. And last, there are honeycomb telescopes, like the LBT. To keep it as light as possible, a hollow honeycomb pattern of support ribs hold the reflective surface and glass.

"(The LBT) has several important features," Atwood said. "There is no piece of glass that's thicker than an inch," this makes the mirror's temperature easier to control. "The reason you don't want temperature gradients in your mirror, is it distorts your mirror. Our mirrors expand and contract with temperature, but they do it very uniformly. It's called 'mirror seeing.' It's a very important thing to control."

A mirror whose temperature differs from the surrounding air can create tiny heat ripples in the air. However, it's not just a hot mirror that has to be watched out for.

"(The problem is) not just warm air," says Atwood, "If the telescope is too cold it will also produce distortion."

Conceived in the late 1980s, the largely Italy-backed LBT has had a long road to completion. Originally, it was scheduled to see "first light" in time for the 2002 Columbus Day celebrations. In fact, it was originally called the Columbus Project. Now, first light is scheduled for some time in 2004.

Atwood is philosophical about the delays. "We always joke about people in space missions," he said. "They can spend an entire career on one project."

Now, as mirror-makers like Atwood near completion of their work, the LBT is finally seeing the light at the end of the tunnel.