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About Dichroic glass

Dichroic (DIE-CROW-ICK) glass, discovered by beadmakers in the early 1990s, has rapidly become a favorite medium for lampworkers. The material, valued for its ability to reflect intense light without producing glare, has been around for years, used widely in medical and photographic applications.

Now, artists are using its unique reflective quality to reproduce the gleaming color combinations that nature's palette had previously reserved for highlighting peacock plumes, the iridescent glow of opals, and occasionally the flash of an insect's wing. For all it's beauty and appeal, it can be a touchy medium to conquer and an expensive one to experiment with. Typically purchased in 16-square-inch sheets, understanding the medium can help the artist predict how it will respond.

What Is Dichroic Glass?

"Dichroic Glass" is somewhat of a misnomer, since the dielectric coating that produces all the interesting colors is not glass at all, but a group of very thin layers of metal oxides. This stack of thin layers has a total thickness of three to five millionths of an inch. The layers produce an "interference filter", creating the varied and unique color characteristics we see. Since the filter is so thin, it has very little mechanical integrity of its own, and must be supported on a mechanically stable substrate. Glass is the ideal candidate for this substrate. Transparent, rigid and stable, it withstands high temperatures, and is not affected by moisture, solvents or most acids. The filter materials are actually more chemically stable than most glasses used as the substrate. Thus, what we commonly call "Dichroic Glass", is actually a piece of dielectric interference filter attached to the surface of a piece of glass.

Characteristics Of Dichroic Glass

To start to unravel the many application possibilities of "Dichroic Glass", the artist needs a fundamental knowledge of its characteristics. The first element that needs to be understood is, that the filter materials are all clear. Secondly, there is effectively no absorption of light by the materials, no dyes, paints or gels. Thirdly, there is a fundamental relationship that all of the light energy is either transmitted, or reflected.

The interference filter produces the colors that we see, by acting as a selective color mirror. The color reflected, is produced by the optical design of the filter. The balance of the light that is not reflected, is transmitted. All of the light energy that hits the filter, must be accounted for in the reflected, and the transmitted light, since none of the energy is absorbed. This is in contrast to a typical piece of colored glass, where the light hitting the surface enters the glass, and part of the color spectrum is absorbed, thus the light energy emitting from the glass, is the color spectrum that is unabsorbed.

The colors available from the typical designs used by most manufacturers are actually a pair of rainbows: one in transmission; and one in reflection. The only difference in the filter, when producing the possible colors, is the thickness of the layers making up the filter.

The interference filter has the unique characteristic of shifting its color as you change the angle of view. As you rotate the filter, the apparent color changes. The intermediate colors will shift down the rainbow. The colors of a natural rainbow are usually considered to be the sequence of violet-blue-green- yellow -orange-red. In the typical, simple, single stack "Dichroic Glass" design used by most manufacturers, the reflective rainbow is similar to the natural rainbow. The transmitted rainbow is, however, in the sequence of yellow-magenta-blue-cyan. Since there is no green or red available in the transmitted rainbow, a second, more complex two stack design, is often used to provide a transmitted rainbow similar to a natural rainbow. This allows a sheet of Dichroic glass to transmit green or red.

The equipment used by the manufacturer has the capability of centering the color of a single sheet of glass, at any point in the available rainbow. There are technical problems associated with maintaining a single color, and the best efforts will vary with each manufacturer.

In the industry today, there are differences in the manner of describing a given piece of "Dichroic Glass". One manufacturer may call the color of the glass the reflected color, and another may call it the transmitted color. Some have even gone to the extent of trying to introduce a third color, produced when the glass is viewed at an angle. Unfortunately, there is no standardization and all names are technically correct, but often confusing. This, coupled with the problem of all the possible variations of the artists' perception of a given color, produces a climate for confusion and misunderstanding. The artist must be familiar with color relationships, so that the obvious possibilities of confusion are minimized. The best approach for communication of Dichroic colors, is a person to person communication between the artist and the Dichroic glass supplier using a set of color samples. Such a session should put the artist in a position to secure colors that will enhance the creative process.

For the artists actively using "Dichroic Glass", a second possibility to eliminate confusion, is to submit desired color samples. All manufacturers should be able to approximate color from a sample. The artist must realize this will only produce approximate results based on the manufacturer's equipment and controls. Each manufacturer will have different degrees of expertise in controlling his processes, and ultimately the colors.

"Dichroic Glass" gives the artist another medium for self expression. The applications are expanding daily, and are limited only by the imagination and ingenuity of the artist.

*Information courtesy of Coatings by Sandberg