Alyssa Dumire, Director of Education
When I consider all the places I encounter glass outside of FWMoA, I tend to think of its more utilitarian applications: windows, simple drinking glasses, magnifiers. In a separate category altogether is glittering crystal, partially because of its more decorative applications and probably also because the name confused me as a kid. Surely the chandelier in my grandmother’s dining room was made from actual diamonds! Spoiler: It wasn’t. What we often call crystal is more accurately termed lead glass. It may be obvious when surveying our Glass Wing that the sculptures are made from a myriad of processes, but perhaps lesser known is that the chemical formula of the glass itself also varies. All glass is primarily made up of silica (basically sand) with a cocktail of other minerals and metal oxides that differentiate the most common glass, soda-lime, from others like borosilicate, used for torchwork and laboratory beakers. When these ingredients include at least 20% lead oxide, it results in a material with exceptional clarity and refraction that is also softer when cool, making it the best choice for intricate carving and optically dazzling sculpture like Christopher Ries’ Sunflower (shown above).
While we often refer to lead glass, especially if cut, as “crystal” because of its resemblance to minerals and gems, glass is technically an amorphous solid. The idea that glass is a liquid, even when cool, is a myth, owing partially to the fact that its molecular structure never aligns into a regular structure as that of most solids. This is true for all forms of glass, but the addition of lead results in other unique properties. Its working temperature is lower, so it requires less energy to heat the furnace. It has a lower viscosity, making it easier to shape in a mold (great for factory production). The cooled glass is softer, allowing for the intricate cut designs in what we know as crystal. Its high refractive index also gives the cut patterns extra sparkle and clarity, aided by the fact that bubbles and other imperfections occur rarely. On the other hand, it cannot withstand sudden changes in temperature (making it more temperamental to sculpt and anneal) and it’s more expensive.
Ancient civilizations around the world made glass, and the formula varied over time and place as artisans experimented with different additives–including lead, which is found in glass dating back to Mesopotamia. Modern lead glass was patented in 1674 by English merchant George Ravenscroft. Ravenscroft was employed by the Worshipful Company of Glass Sellers of London to develop an alternative to the imported Murano cristallo. His first batches, while perfectly clear initially, revealed flaws over time through a process called crizzling. His “flint glass,” as crystal is still sometimes known, was made from silica derived from calcined flint, and the addition of lead resulted in the quality sought by his financiers. This invention ushered in a new era of glassmaking for England: by 1696, nearly all of the glass producers in London were using flint glass, which became a hot commodity on the Continent.
The unique properties of lead glass are aesthetically important to be sure, but they also impacted its development economically. Its density is relatively high, and glass was sold by weight, making it a high earner for its producers. In 1746, owing to the popularity of its exports, the British government imposed a lucrative tax, also by weight. Cut patterns, more easily carved due to lead glass’ softness, removed some of the bulk, as did hollow goblet stems. This impacted the prevailing taste: while simple, unadorned glass vessels were sufficiently beautiful before, ever more intricate cut crystal became the fashion. When Ireland was granted duty-free glass trade, English glassmakers largely relocated the industry there, most famously, to Waterford. Across the pond, the crystal craze continued through the turn of the twentieth century, with the makers of American Brilliant-Period cut glass developing dazzling innovations to standard patterns. In 1932, scientists at Corning Glassworks developed a lead glass with even greater optical clarity, fueling their division, Steuben’s, production of Art-Deco era housewares.
While lead crystal is still a popular choice for decorative objects and was long considered safe for eating and drinking, in 2011, the World Health Organization declared that no level of lead intake was safe. It can leach into food served from it, especially if acidic or alcoholic, meaning those crystal decanters are best used as a vase, not for actually serving wine. There is even a correlation between high levels of gout in the upper classes and their tendency to use such vessels. Lead glass has industrial applications as an insulator for electrical wiring and as a shield from radiation thanks to its density. And, of course, since the start of the Studio Glass movement in the 1960s, artists began experimenting with it as a purely sculptural material.
How can you tell if a glass work is crystal? Because the material is more dense; a piece made from lead glass will be heavier than a comparable piece of standard soda-lime. You can also give it a tap or a flick with your fingers and listen: it should ring! Obviously you can’t do either of these at the museum, so luckily there are also some visual cues. Take a look at another sculpture by Christopher Ries from two different viewpoints:
If a work of glass sculpture makes you go “whoa dude” as you move around it, odds are, it is lead glass. This is refraction in action, the property that causes crystal to bend light more efficiently than other varieties of glass, distorting the image we see through it in surprising ways. It often acts as a prism, scattering light into its different wavelengths (kids are pros at finding the little rainbows on walls and pedestals). Also note the exceptional clarity when looking through the flat side of the sculpture. You could say it’s crystal clear!
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