What Dichroic Glass Is
Dichroic glass shows different colors depending on how light hits it. It’s made by layering metal oxides in a vacuum chamber. These thin layers bend light in ways that change color based on the viewing angle. You often see it in stained glass, jewelry, and art pieces. The term “dichroic” can mean two colors, but sometimes it’s trichroic, showing three or more tones, or even iridescent. In labs, they use “dichroic” more precisely for interference filters.
Ancient Roman Dichroic Glass
Back in the 4th century AD, Roman artisans made a different kind of dichroic glass. They mixed tiny gold and silver particles directly into the glass. That meant the glass looked one color when light hit it from the front, and another when lit from behind. The Lycurgus Cup, now in the British Museum, glows green in normal light and changes to purple-red when light shines through it. This effect isn’t from metal films but from the precious metal particles in the glass. Ancient texts like Achilles Tatius’s Leucippe and Clitophon mention cups that change from green to red, showing this technique was known in antiquity.
Renaissance and Later Uses
After the Romans, this glass technique disappeared until the Renaissance in Venice, where artists revived it. These pieces are still rare today, and today’s versions are rooted in that blend of art and science.
Modern Production: NASA’s Role
Today’s dichroic glass owes a lot to NASA and its contractors. They needed special filters, so they developed the methods used now. Even though color-changing glass has roots in the 4th century, modern production uses high-tech coatings.
How It’s Made Today
To make modern dichroic glass, manufacturers vaporize ultra-thin layers of transparent metal oxides like titanium, chromium, aluminum, zirconium, magnesium, or silica. They do this inside a vacuum using an electron beam. The vapor settles on glass, forming crystal-like layers. Sometimes they add a quartz layer on top to protect it. You can get up to 30 to 50 layers, but the total thickness is just 30 to 35 millionths of an inch (around 760 to 890 nanometers). These coatings act a bit like gemstones. By controlling the thickness of each layer precisely, makers bring out different colors.
How Light Works with Dichroic Glass
All the light that hits a dichroic layer ends up either reflected or passing through. When you fuse a plate of dichroic glass with other glass in a kiln, each firing job turns out differently. That means every fused piece is truly one of a kind. You can choose from over 45 coating colors and use them on any glass base.
Uses in Optics
People use dichroic glass in optical filters. It picks out very narrow bands of color. You’ll find it in things like fluorescence microscopes, LCD projectors, and even 3D movie systems.
Uses in Glass Art
Glass artists now buy coated glass straight from dichroic coating makers. They often call it “dichro.” Artists can remove parts of the coating to make designs, letters, animals, or faces. They usually do that with a laser for precision.
You can work these coated sheets in heat or use them plain. You can shape and fuse raw glass in a kiln, then apply the coating afterward. That gives you reflective forms with changing color effects.
Stunning Architectural Examples
Dichroic glass isn’t just for small art. Take Amazon’s Seattle headquarters. Its towers use dichroic glass on the outside to reflect changing hues all day long. The glass looks different depending on the sunlight.
Another example is the Museum at Prairiefire in Overland Park, Kansas. It opened in May 2014 and focuses on natural history. Its exterior glass is dichroic, too. The colors change with the light, echoing the idea of prairie fires and paying tribute to old Kansas farming life.
