Flood Threatens Photographic Plates

A burst pipe flooded Harvard College’s Observatory Hill, submerging thousands of historic photographic plates underwater. Recovery is now under way to save these astronomical images.

Building D of the Harvard College Observatory houses three stories of shelves crowded with snapshots of the sky. These photographic plates, beautiful “film negatives” made of glass, were taken by astronomers both at Harvard and at outposts around the world over the years 1885 to 1992. The observatory stored them here in carefully marked paper envelopes as a large-scale celestial recordkeeping project. The collection contains more than 500,000 plates; no one is quite sure of the exact number. With more than a century of data preserved, the archive is the Alexandrian library of astronomy.

But on the morning of January 18th, there was something else in the stacks besides the glass: water.

At about 5:30 a.m. that Monday morning, the Cambridge city water main running beneath Observatory Hill ruptured. The plate collection is housed to protect it from fire and various other mishaps, but no one could have predicted this 8-inch pipe would burst some 16 feet beneath the courtyard outside. Being at the top of the hill, the busted pipe could have sent its water in any direction. Due to the vagaries of underground soil, however, it sent it straight for the observatory buildings, including the basement beneath the stacks.

With 60 pounds of water pressure, the burst main was like “a fire hydrant on steroids,” laments astronomer Jonathan Grindlay (Harvard), who directs the project to digitize all 500,000-plus plates, called Digital Access to a Sky Century at Harvard (DASCH). The water filled the 5-foot-deep basement beneath the stacks first. At 8:30 a.m., when DASCH staff discovered the flood, there were 2 feet of standing water in the archive’s bottom story. By the time the water was turned off, the level had risen above 3 feet.

The water soaked the four lowest shelves of paper-shrouded plates. It also destroyed a half dozen computers and the commercial scanner the team was using to digitize the archive. “Electronics do not like to be submerged in muddy water,” Grindlay sums up.

Scrambling to save the collection, the team called up Harvard’s Weissman Preservation Center, whose staff had already been advising DASCH. Turns out the Weissman folks are set up for emergency response. They showed up with a couple thousand foldable plastic boxes, each about 1½ ft wide, designed to store valuable documents under threat. Over three days, staff and volunteers packed each box with about 30 plates and ferried it out in “a sort of human bucket brigade,” Grindlay says. By Thursday afternoon they had evacuated the bottom rows of plates — some 61,000 in all, each in its soaked paper envelope.

The Recovery Plan

The first order of business, the Weissman experts told DASCH’s staff, was to freeze the plates. Old photographic glass in sopping paper might sound bad, but it’d be far worse if the paper started molding. Fortunately it was a cold week in the Boston area, giving rescuers time to have the 2,000 or so boxes trucked up to North Andover for storage in three semi-trailer freezer cars, like a makeshift astronomical cryogenics lab.

Over the next year and a half, disaster recovery contractors will carefully thaw and photograph each plate — still in its envelope — by hand, before removing the paper and gently cleaning the plate itself to preserve the photographic emulsion. After a plate is cleaned and dried, it’ll slide into a new, barcoded sleeve.

After extensive checks, Grindlay says they're confident that they haven't lost the plates; they'll be able to clean and scan them and finish the DASCH project, which is only about a third done. (The flooded shelves haven't been scanned yet.) Certainly the envelopes are ruined, but the notes on them are duplicated in the archive’s ledgers, and the plate number is also printed on the glass itself.

There are a few silver linings in this disaster. First, all the custom-built equipment survived, including the one-of-a-kind plate-cleaning machine. Second, the commercial scanner DASCH was using was 10 years old, and the new one they’ve ordered should be about twice as fast. It’s being built and will be delivered in about four months. Third, thanks to the new scanner, the team should be able to make up most of the lost time, finishing the digitization project in early 2018 instead of the end of 2017.

Oh, and fourth: insurance is footing the bill.

There’s still plenty to be done — floor tiles to replace, restoration procedures to finalize — but in all only 12% of the collection was flooded; the other plates still remain safe and dry on their shelves, ready for eager astronomers to study.