Dichroic glass is glass

Glass

Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...

 containing multiple micro-layers of metal

Metal

A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...

s or oxides which give the glass dichroic optical properties. The main characteristic of dichroic glass is that it has a particular transmitted color and a completely different reflected color, as certain wavelengths of light either pass through or are reflected. This causes an array of color to be displayed. The colors shift depending on the angle of view. Dichroic glass is an example of thin-film optics

Thin-film optics

Thin-film optics is the branch of optics that deals with very thin structured layers of different materials. In order to exhibit thin-film optics, the thickness of the layers of material must be on the order of the wavelengths of visible light...

.

Invention

Modern dichroic glass is available as a result of materials research carried out by NASA

NASA

The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

 and its contractors, who developed it for use in dichroic filter

Dichroic filter

A dichroic filter, thin-film filter, or interference filter is a very accurate color filter used to selectively pass light of a small range of colors while reflecting other colors. By comparison, dichroic mirrors and dichroic reflectors tend to be characterized by the color of light that they...

s. However, dichroic glass dates back to at least the 4th century AD, as seen in the Lycurgus cup

Lycurgus cup

The Lycurgus Cup is a Roman glass cage cup now in the British Museum, made of a dichroic glass, which shows a different colour depending on whether or not light is passing through it; red when lit from behind and green when lit from in front...

.

Manufacture

Multiple ultra-thin layers

Thin film

A thin film is a layer of material ranging from fractions of a nanometer to several micrometers in thickness. Electronic semiconductor devices and optical coatings are the main applications benefiting from thin film construction....

 of different metals (such as gold

Gold

Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...

 or silver

Silver

Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...

); oxides of such metals as titanium

Titanium

Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....

, chromium

Chromium

Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...

, aluminium

Aluminium

Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

, zirconium

Zirconium

Zirconium is a chemical element with the symbol Zr and atomic number 40. The name of zirconium is taken from the mineral zircon. Its atomic mass is 91.224. It is a lustrous, grey-white, strong transition metal that resembles titanium...

, or magnesium

Magnesium

Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...

; or silica

Silicon dioxide

The chemical compound silicon dioxide, also known as silica , is an oxide of silicon with the chemical formula '. It has been known for its hardness since antiquity...

 are vaporised

Electron Beam Physical Vapor Deposition

Electron Beam Physical Vapor Deposition or EBPVD is a form of physical vapor deposition in which a target anode is bombarded with an electron beam given off by a charged tungsten filament under high vacuum. The electron beam causes atoms from the target to transform into the gaseous phase...

 by an electron beam in a vacuum chamber

Vacuum chamber

A vacuum chamber is a rigid enclosure from which air and other gases are removed by a vacuum pump. The resulting low pressure, commonly referred to as a vacuum, allows researchers to conduct physical experiments or to test mechanical devices which must operate in outer space...

. The vapor then condenses on the surface of the glass in the form of a crystal structure. A protective layer of quartz

Quartz

Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...

 crystal is sometimes added. Other variants of such physical vapor deposition (PVD)

Physical vapor deposition

Physical vapor deposition is a variety of vacuum deposition and is a general term used to describe any of a variety of methods to deposit thin films by the condensation of a vaporized form of the desired film material onto various workpiece surfaces...

 coatings are also possible. The finished glass can have as many as 30 to 50 layers of these materials, yet the thickness of the total coating is approximately 30 to 35 millionths of an inch (about 760 to 890 nm). The coating that is created is very similar to a gemstone

Gemstone

A gemstone or gem is a piece of mineral, which, in cut and polished form, is used to make jewelry or other adornments...

 and, by careful control of thickness, different colors may be obtained.

The total light that hits the dicro layer equals the wavelengths reflected plus the wavelengths passing through the dichro layer.

A plate of dichroic glass can be fused

Fused glass

Fused glass is a term used to describe glass that has been fired in a kiln at a range of high temperatures from to . There are 3 main distinctions for temperature application and the resulting effect on the glass....

 with other glass in multiple firings. Due to variations in the firing process, individual results can never be exactly predicted, so each piece of fused dichroic glass is unique.
Over 45 colours of dichroic coatings are available to be placed on any glass substrate.

Optics

Dichroic glass is used in various dichroic optical filters

Dichroic filter

A dichroic filter, thin-film filter, or interference filter is a very accurate color filter used to selectively pass light of a small range of colors while reflecting other colors. By comparison, dichroic mirrors and dichroic reflectors tend to be characterized by the color of light that they...

 to select narrow bands of spectral

Spectrum

A spectrum is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a prism; it has since been applied by...

 colors, for example in fluorescence microscopy, LCD projectors, or 3D movies.

Artists

Dichroic glass is now available to artists through dichroic coating manufacturers. Glass artists often refer to dichroic glass as "dichro".

Images can be formed by removing the dichroic coating from parts of the glass, creating everything from abstract patterns to letters, animals, or faces. The standard method for precision removal of the coating involves a laser

Laser

A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...

.

Dichroic glass is specifically designed to be hotworked

Warm glass

Warm glass or kiln-formed glass is the working of glass, usually for artistic purposes, by heating it in a kiln. The processes used depend on the temperature reached and range from fusing and slumping to casting....

but can also be used in its raw form. Sculpted glass elements that have been shaped by extreme heat and then fused together may also be coated with dichroic afterwards to make them reflect an array of colors.