Buying Art Glass

Have you really considered the language used for art glass? Most find these terms both numerous and perplexing, so much so that I threw a ringer right in the title. For starters, as most of us learned in elementary science class, mica isn’t glass at all. Instead it’s a mineral. But mica flakes nicely into translucent sheets, making it ideal for use in lamp shades, such as the famous “coolie” shades made by Dirk van Erp.

“Art glass” is certainly a catch-all term that can be used to refer to most kinds of decorative glass in period lighting, windows, doors or hand-blown vases, but terms do exist that are more accurate and specific. First let’s start with a tough one: the difference between stained and leaded glass. In historical European cathedral windows and the like, this stained glass is colored glass that’s been painted with vitreous oxides and fired with or without silver nitrate. What makes this stain glass leaded is that individual pieces of the composition are held together with lead cames, which are easily recognizable as the rib-like dark material between the bits of light-filled glass.

These days, things are much simpler. Modern usage of the term “stained glass” is considered by most people to be any window with colored glass. If a clear glass window is leaded, it’s just simply call “leaded.”

Minerals give colored glass its tint. However, not all stained glass is transparent. Translucent stained glassed are most commonly known as “opalescent.” But be careful. Opalescent glass is not transparent but rather milky. This type of glass often has more than one color in a sheet. A great example of opalescent glass is Tiffany windows.

Another notable example of this is the windows by Greene & Greene, who layered their glass the same way as Tiffany, but they used copper foil and lead overlay to enhance the dimensional quality of their compositions. Like their oak beds and their oak dressers the glass made by Greene & Greene is actually a very common glass. It’s iridized on one side, so it has the appearance of a rainbow. Both Frank Lloyd Wright and Tiffany have used the same glass.

In 1894, Tiffany trademarked its version of this shimmering opalescent glass and called it Favrile. This iridescent glass is truly remarkable, as it appears to change colors when viewed from various angles. Although iridized glass was produced and marketed by many other companies, none used the name Favrile.

We’ve clarified what mica, stained glass, leaded glass, opalescent, iridescent, and Favrile all are. What exactly are slag and slumped? Well, slag glass is the term used for the sheets of opalescent glass slipped into Arts and Crafts light fixtures. (The term “slag” refers to the undocumented belief that slag from iron smelting works was added to the glass for color.) On the other hand, slumped glass refers to glass that’s been worked when still hot in the kiln. Glass artisans will actually get into the kiln to manipulate the glass into shades, which are first “slumped” over a bowl. Artists can even create more complicated shapes, ranging from delicately folded glass in a tulip-like shade to futuristic shapes that resemble a translucent article marshmallow after a swipe through the campfire.