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Crack a Window into the Art of Glass Preservation | Conservation Lab

The tiny city of Corning, New York is home to the world’s best glass conservators.
Lead image: Stephen Koob, chief conservator at the Corning Museum of Glass, working on a model from the Blaschka collection of marine invertebrates. All photos courtesy of Corning Museum of Glass, unless otherwise noted.

The small city of Corning, New York, population 11,068, counts more works of art than people. The world's largest collection of glass art is harbored here, at the Corning Museum of Glass, which cares for over 50,000 objects spanning 3,500 years of history. Across the Chemung River, a short walk away, lie the headquarters of Corning Incorporated—the glass and ceramics manufacturing giant responsible for the creation of brands like CorningWare and Pyrex. The company founded the museum in 1951, as a "gift to the world" to mark its 100th anniversary. The museum's facilities have grown tremendously since then: In addition to gallery spaces, they include a research library, glassmaking studios, and an amphitheater for live demonstrations.


Conservation lab at the Corning Museum of Glass, with associate conservator Astrid van Giffen (left) and Stephen Koob.

Behind the scenes, two leading glass conservators care for the museum's vast collection, preparing the fragile objects that go on display. Associate conservator Astrid van Giffen takes me around the lab, beginning the tour around the treasured plastic sink, where almost all of the glass that comes in is washed. If the glass is deteriorating, washing it can slow down that process, and eliminate any deposits that have settled onto the surface. Yet moisture, I quickly learn, is often the enemy. If a glass object is left in a high humidity environment, or if a single drop of water is trapped inside, it can lead to "crizzling," a network of micro-cracks that deepen with time. "It's funny that a material we think of as very stable is actually most vulnerable to water," comments van Giffen. If the crizzling is particularly advanced and reaches what's called the fragmentation stage, the object will become so weak that it falls apart on its own, without any impact with another surface.

Favrile Kerosene Lamp with Morning Glory Shade and Peacock Feather Base by Louis Comfort Tiffany, before and after restoration.

While the process of crizzling can be slowed down, it cannot be reversed. In comparison, an object that has shattered because of mishandling suddenly seems like a much less complicated problem: In those cases, restoration is usually possible. "I love puzzles!" laughs van Giffen. "My favorite conservation projects are the ones where I have 100 fragments to put back together." In 2011, her colleague, chief conservator Stephen Koob, restored a rare Tiffany Peacock Eye lamp base that had broken into 40 pieces, plus hundreds of tiny chips of glass. The lamp was donated to the museum after suffering an accident during a home renovation. Koob spent months on the project, gluing just one to three pieces per day and leaving them to dry.


Pitcher from the Roman Empire, before and after restoration.

Like any other jigsaw puzzle, there is little room for error: "If you make a mistake, you get a lock-out, with pieces left over," explained Koob at the time, in a museum article. Luckily, the veteran conservator has come up with some innovative solutions throughout his career. Several decades ago, he began using an acrylic adhesive that can easily be removed if a mistake is made, but that remains incredibly stable over time. During our tour, van Giffen shows me the pellets of this magical plastic resin, named Paraloid B-72, which, depending on the recipe, can be used as an adhesive, or even cast and used to fill in missing pieces. Simply put, "it's the best thing ever," she tells me. "It is used for varnishing paintings, but Stephen brought it into common use in glass and ceramics conservation."

Above, acrylic fills setting in their molds. Below, shaping the fill with heat. Photos by the author.

In one corner of the lab, an intern is practicing how to make infills with this method, which Koob and van Giffen began developing about a decade ago. Colored with different dyes, several acrylic fills are set inside little rectangular molds. Later, they can be cut and shaped with a little heat to perfectly match the missing glass fragment. The results are sometimes so convincing that it can lead into dangerous territory, ethically speaking, since conservation treatments should remain visible as such. But, van Giffen assures me, in glass conservation, "You can always see, because we never use glass to fix glass—it's not safe. It's always a different material."


Engraved goblet from Potsdam, about 1690-1700, with an old restoration done with wood.

Upstairs in the galleries, a goblet repaired long ago with a wooden foot provides an example of archaic glass restoration methods. Materials were different back then, as were ethics: Restorers sometimes assembled two incomplete objects together to make a whole, which would be unconscionable by today's standards. I ask van Giffen what she would do if such an object landed in her care: If it's structurally stable, do you still undo the old restoration, or leave it be? "That's a good question…because now, that's become part of the history of the object." We leave it there. Speaking hypothetically in this field yields few answers: Until you have the object under the microscope, you can't possibly know what direction you'll take.

Conservators inspect glass objects under UV light to determine the composition of the glass. Pictured here is an object from the Blaschka collection of marine invertebrate models. 

Blaschka model during treatment. Conservators will glue back broken pieces in their rightful place by figuring out which "glue scars" from the original adhesive fit together. Photo by the author.

Pigments and dyes. Photo by the author.

A mold of a missing piece was created with a plaster fill (farthest right). Epoxy fills that are dyed to match the blue of the original glass can then be created. Photo by the author.

For more information about conservation at the Corning Museum of Glass, go here. Videos of the conservation team at work are available here.


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