Stained glass

Stained glass is both a beautiful art form and a complex architectural material. It refers to colored glass used in artistic works or structural pieces. While most people think of flat window panels, modern artists also create three-dimensional sculptures. The term can even describe domestic items, such as the famous lamps made by Louis Comfort Tiffany.

Beyond simple decoration, these works serve a specific purpose in building design. They are often called "illuminated wall decorations" because they control light rather than just letting it in.

Creating a functional window requires a mix of artistic vision and engineering precision. An artist must conceive a design that is actually workable in glass. The finished piece must fit snugly into its designated space. It also has to withstand environmental pressures like wind and rain. For very large installations, the window must be strong enough to support its own weight. Many large windows from the Late Middle Ages have remained intact for centuries due to these careful construction methods.

To build a window, small pieces of colored glass are arranged into patterns or pictures. These pieces are held together by strips of lead known as cames or calms. The entire assembly is then held by a rigid frame. Artists often add extra detail using painted elements. They might use silver stain to create yellow colors. To define shapes and add shading, they use a dark mixture called grisaille paint. This paint contains powdered glass, iron or rust filings, clay, and a binder like gum arabic. The glass is then fired in a kiln to fuse these details to the surface.

The glass itself begins as a molten mixture of silica. Because silica requires extremely high temperatures to melt, makers add potash, soda, or lead to lower the melting point. They also add lime to make the glass more stable. Color is introduced by adding metallic oxide powders while the glass is molten. For example, cobalt creates a deep blue, while copper oxides produce green or bluish-green shades. Gold can produce violet or wine-red glass. However, modern red glass often uses copper because it is less expensive and provides a bright, vermilion shade.

There are two primary ways to color the glass: pot metal and flashed glass. Pot metal glass is colored all the way through the sheet. This happens when the color is mixed directly into the clay pot in the furnace. Flashed glass is a different technique used to solve a specific problem with red glass. If red glass is made at a standard thickness of 3 mm, the color is so intense that it looks black. To fix this, makers laminate a thin layer of red glass onto a thicker piece of clear or lightly tinted glass. This "flashing" allows light to pass through while maintaining a rich color. Artists can also engrave or abrade flashed glass to reveal the clear layer underneath.

Glassmakers use several methods to turn molten globs into flat sheets. In the cylinder or "muff" method, a maker gathers molten glass on a blow-pipe and blows an air bubble. They use tools, gravity, and water-soaked wooden molds to shape it into a long cylinder. Once the desired size is reached, the cylinder is cut, heated, and flattened. Another traditional method is crown glass. A maker blows a bubble and spins it rapidly on a table. Centrifugal force flattens the bubble into a disk. This process leaves a thick center called a "bull's-eye" and a distinctive pontil mark.

Historically, different civilizations have advanced the craft of glassmaking. From the 8th century onward, Islamic civilization played a major role in the development of stained glass. Through scientific progress in chemistry and optics, Islamic glassmakers turned the craft into a large-scale industry. They produced glass vessels in massive quantities by blowing liquid glass in chambers. In Syria and Egypt, artisans developed unique techniques for coloring and decoration. Syrian stained glass is particularly famous for its intricate geometric and floral designs. This tradition of excellence continues today in factories across Germany, the United States, England, France, Poland, Russia, and Syria.