Neon signs are composed of two or more electrodes that complete an electrical circuit. When gas is ionized inside one electrode by applying high voltages, free electrons are forced into the tube walls. These electrons can then jump across gaps in the tubing at either end of the tube, where they will hit oxygen molecules and cause them to give off light (the same process occurs in neon lights and fluorescent lamps).
The color emitted in a neon sign is directly dependent on which gases fill the tubes: if the air is used instead of “neon,” red will be emitted; methane produces orange; helium causes glowing white; argon emits purple; mercury vapor gives blue-green; xenon results in bright yellow; and pink is achieved by adding carbon monoxide.
There are two methods of making a neon sign: sketch and etch neons. Sketch neons, also known as hand-painted or hand-drawn neons, usually have white or yellow glass tubing colored using paintbrushes to produce the desired color in the finished product. In contrast, etch neons are almost exclusively made from clear glass tubing with an internal coating of phosphor—this phosphor coating emits light when excited by electrons from the electrodes at either end of the tube. This difference in the process means that in a sketch neon, each electrode must be separately manufactured, coated with a separate color/composition to make it react to electricity in a different way (the electrodes used to produce red, orange, and yellow colors are different from those that make green, purple and blue colors).
It is also necessary for sketch neons to have multiple layers of colored glass tubing running throughout the sign (to make the white/yellow base color visible), whereas etch neons can generally be made using clear glass tubing with a phosphor coating.
Etch neon signs are created by placing a mask over the internal surface of the glass tubing—this mask has cutouts that allow electric current access to each electrode. Once this mask is in place, an inert gas (usually argon) is pumped into the tube where it displaces any air inside; next, electricity at very high voltage is passed through the electrodes at each end of the tube. The high voltage causes a portion of this gas to ionize, and free electrons are forced into the glass wall. These electrons then collide with atoms in the tube’s atmosphere, exciting them and causing them to release photons that result in light being emitted from different parts of the tube.
The color emitted by a neon sign is directly dependent on which gases fill its tubing: if the air is used instead of “neon,” red will be emitted; methane produces orange; helium causes glowing white; argon emits purple; mercury vapor gives blue-green; xenon results in bright yellow; and pink is achieved by adding carbon monoxide. The color mix inside single-color neon tubes can vary significantly due to slight variations in the gases used.
Neon tube signs are often created using glass tubing filled with different gas mixtures to make colors or colored glass tubing that has had metal powder dusted onto its inner surfaces during manufacture. Painted finishes are also standard on sketch neons due to their hand-made nature—in contrast, etch neons are almost exclusively made from clear glass tubing with an internal coating of phosphor (which emits light when excited by electrons at either end of the tubing).