GLASS OF THE ALCHEMISTS

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From Mystics to Chemists

By MARK YOST

August 20, 2008; Page D9

Corning, N.Y.

Alchemists have a much-deserved bad reputation. Throughout the Middle Ages and into the Renaissance, many of them were nothing more than mystical con men, hell-bent on bilking European royal families, aristocrats and anyone else with a spare coin into believing that they'd figured out how to "make" gold and other precious metals. But from about 1650 to 1750, alchemists had what was arguably their greatest -- and most honest -- century.

"Glass of the Alchemists," a special exhibit at the Corning Museum of Glass through Jan. 4, tells this story well and features some of the finest lead-crystal and gold-ruby pieces produced during this extraordinary period of advancement in the art and science of glassmaking.

Laying the historical groundwork, the exhibit opens with a reproduction of a 17th-century alchemist's workshop. Here he would have toiled to prove the alchemist's central thesis that everything is made up of four essential elements -- earth, air, fire and water. But it was during this period that some of alchemy's practitioners began to transform from "mystics to chemists," said David Whitehouse, the museum's executive director, who leads a free tour on Wednesday mornings. Indeed, he reminds us that Sir Isaac Newton remained a devout alchemist long after his important discoveries in the physical world.

Before this renaissance in glassmaking, most glass was still made from three basic elements: silica, potash and chalk. Most of the glass produced before the 17th century was colorless and of good quality. And while there was engraved glass, intricacy and depth were limited by the thinness and fragility of the glass.

George Ravenscroft, an English glassmaker, first started adding lead to his formula in the mid-17th century. It was not an easy process. He not only had to have the right formula, but the materials -- which were superheated to more than 2,000 degrees Fahrenheit -- had to be cooled slowly. To do this, Ravenscroft and others built elaborate kilns that had hot spots for melting and strategically placed vents that created controlled drafts for cooling. A ½-scale model of one of these ovens -- which would have been about 16 feet tall and perhaps 20 feet around -- is on display here.

When done properly, the process created a glass that was -- pardon the pun -- crystal clear, because the lead changed the way the glass refracted light. According to a large display panel here, the proper formula was 150 pounds sand or flint, 100 pounds of potash, 20 pounds of chalk and just five ounces of manganese.

Get this formula wrong, however, and the finished glass would be unstable. It would continue to absorb moisture from the air and become cloudy in a process called grizzling. Thanks to the wonders of modern atmospherically controlled display cases, you can see one of Ravenscroft's early mistakes (it looks like a frosted mug).

Once he'd perfected his formula and process, Ravenscroft foiled forgers by putting a small bead on all his pieces with a raven's head. Several of these highly valuable pieces, including a rum goblet made at Ravenscroft's Savoy Glasshouse in London c. 1676, are on display here.

The other contribution from alchemists during this period was ruby-gold glass, which has a distinctive red hue. The problem had long been dissolving the gold down to precise nanoparticles. If the particles were too small, they wouldn't scatter the light along the proper spectrum and the glass would appear clear. Too big, and the glass had a turbid, brownish color.

One of the simplest but most beautiful pieces on display is the Covered Goblet with 'Fruit Children.'

The key breakthrough came in 1659, when alchemist Johann Rudolf Glauber published a paper describing how to make purple of Cassius. Using an ancient formula called aqua regia, a mix of nitric and hydrochloric acid used to dissolve gold, Glauber added a small amount of tin, which reacted with the gold to produce perfectly sized particles.

Glassmaker Johann Kunckel used the purple of Cassius formula to make the first ruby-gold vessels in the 1680s. The coloring of the pieces is exquisite. Thanks to cooperation from museums around the world, the Corning Museum has brought together some of the finest examples of these works.

One of the simplest but most beautiful pieces is the Covered Goblet with "Fruit Children," on loan from the Focke-Museum in Bremen, Germany. The goblet itself is an almost cylindrical bowl with a beveled rim and rounded bottom, cut into 12 panels. The color is a light raspberry.

Of course, there were mistakes. The Overlay Beaker is a Bohemian piece from the late 17th century on loan from the Museum of Decorative Arts in Prague. The glassmaker used copper instead of gold in the mixture. The result is a piece that's almost pitch black.

While the exhibit is almost exclusively focused on the good that alchemists did during this period, it concludes with the tale of Johann Friedrich Böttger, an alchemist who was imprisoned by Augustus the Strong, king of Saxony and Poland. Augustus put the ultimate alchemist's challenge to Böttger: Make me gold. Böttger claimed that he did just that, and won his freedom in 1714. The nugget, which has been certified to be gold, is on display here.

The final panel of the display asks, "Did Böttger really make gold?" The answer, of course, is "no." He obviously used some old alchemist's trick to fool the king. But as this exhibit makes clear, alchemists did much to advance the art of glassmaking in the 17th century. To learn this story and see these pieces up close, it's well worth the trip to upstate New York.