Art Stained Glass is an art form in which colored glass is cut to fit a design and joined together (usually with lead) to form a window, lampshade, or decorative panel.

It is unique among the visual arts because it relies entirely on transmitted light. While a painting reflects light off its surface, a stained glass window comes to life only when light passes through it. It is often described as “painting with light.”

Here is a minute, detailed breakdown of the world of Stained Glass.

1. The Chemistry: How Glass Gets Color

Glass is made of silica (sand), potash | soda (flux), and lime (stabilizer). In its pure state, it is clear or slightly green. Color is added by mixing metallic oxides into the molten glass while it is in the pot (Pot Metal Glass).

Cobalt Oxide: Creates deep Blue.
Gold Chloride: Creates rich Ruby Red (the most expensive color to produce).
Selenium: Creates Yellow or Orange.
Copper Oxide: Creates Green or Red (depending on the oxidation state).
Manganese: Creates Purple (or neutralizes green).

2. The Two Primary Construction Techniques

In your marketplace, distinguishing between these two methods is vital, as they dictate the value and the era of the piece.

A. Lead Came (The Medieval/Architectural Method)

This is the traditional method used for church windows for over 1,000 years.
The “Came”: The glass pieces are held together by H-shaped strips of lead called “cames.” The glass slides into the grooves of the H.
Soldering: The lead strips are soldered together only where they join (the joints).
Cementing: A putty (cement) is forced under the lead flanges to waterproof the window and stop it from rattling.

B. Copper Foil (The Tiffany Method)

Invented | Popularized by Louis Comfort Tiffany in the late 19th century to create complex lamps and detailed curves that lead came could not handle.
The Process: Every single piece of glass is wrapped on the edges with adhesive Copper Tape.
Soldering: The pieces are butted together, and solder (tin/lead alloy) is melted along the entire length of the seam, bonding the copper tape together.
Look: Fine, variable-width lines. Allows for 3D shapes (lampshades) and tiny, intricate pieces.

3. Glass Types (Inventory Categories)

Collectors look for specific types of glass.

Cathedral Glass: Transparent, single-color glass. You can see through it. Used in Gothic churches.
Opalescent Glass: Semi-opaque or milky glass. It reflects light as well as transmitting it. This was the hallmark of Tiffany and La Farge. It looks like marble or gemstones.
Flash Glass: A sheet of clear glass with a razor-thin layer of colored glass blown onto the surface. Artists can etch/sandblast the color away to reveal the white underneath (used for detailed heraldry).
Rondels: Circular, spun discs of glass with a “bullseye” in the center. Historically, this was the center of the blown glass sheet.

4. Painting on Glass (Grisaille)

Contrary to popular belief, the details (faces, hands, drapery folds) in stained glass are not created by different pieces of glass; they are painted on.

Vitreous Paint: A mixture of ground glass and iron oxide. It is brown or black.
The Process: The artist paints the shadow and line work onto the colored glass. The glass is then fired in a kiln. The paint fuses into the surface of the glass and becomes permanent.
Silver Stain: A silver nitrate compound painted onto the back of the glass. When fired, it turns clear glass into a glowing Yellow/Gold. This technique (invented in the 1300s) is actually the origin of the term “Stained Glass.”

5. Historical Movements

A. Gothic (1100–1500)

Purpose: To educate the illiterate (“The Bible of the Poor”) and create a spiritual atmosphere (The “Lux Nova” or New Light).
Style: Rose windows, deep reds and blues, mosaic-like complexity. (e.g., Chartres Cathedral, Notre Dame).

B. The Arts & Crafts (1860–1910)

William Morris: Returned to the medieval lead-came technique but with domestic subjects (knights, literature, flowers). Used predominantly in English homes.

C. Art Nouveau | Tiffany (1890–1910)

Louis Comfort Tiffany (USA): He revolutionized the art by creating glass that had texture and multi-colored swirls inside the material (favrile glass), reducing the need for painting. He focused on nature (dragonflies, wisteria, peacocks).

D. Prairie Style (1900–1920)

Frank Lloyd Wright: He called his windows “Light Screens.” He used mostly clear glass with geometric touches of primary colors and gold. The design was about the lead lines (zinc came) creating a geometric grid.

6. Assessing Condition (Valuation)

For your marketplace, condition reports are critical for stained glass.

Bowing: Does the window bulge in or out? This means the lead has fatigued and the window is collapsing under its own weight.
Light Leaks: Can you see daylight between the glass and the lead? The waterproofing putty has fallen out.
Cracks:
Stress Crack: A clean line usually starting from the edge (caused by heat or pressure).
Impact Crack: A “spiderweb” or shattered point (caused by a rock or object).
Solder Bloom: White, powdery corrosion on the lead lines (lead disease).
Origin Medieval | Traditional 19th Century | Tiffany
Line Width Thick, uniform Thin, variable
Structure Rigid, Heavy Flexible, Lighter
Application Windows, Doors Lamps, Suncatchers
Aesthetic Architectural, Bold Intricate, Organic

The Objects: (Furniture, Ceramics, Glass).
The Methods: (Oil, Watercolor, Hatching, Stained Glass).
The History: (Renaissance through Photorealism).

Art Stained glass