Neon

Neon signs are produced by the craft of bending glass tubing into shapes. A worker skilled in this craft is known as a glass bender, neon or tube bender.

History
The neon sign is an evolution of the earlier Geissler tube (also called a Crookes tube), which is a glass tube for demonstrating the principles of electrical discharge. Neon signs are used for many purposes.

At the 1893 World's Fair, the World Columbian Exposition in Chicago, Illinois, Nikola Tesla's neon lamp signs were displayed. The development of neon signs is credited to Georges Claude and the first public display of a neon sign was of two 38-foot long tubes in December of 1910 at the Paris Expo. The first commercial sign was sold by Jaques Fonseque, Claude’s associate, in 1912 to a Paris barber.

Manufacturing Process
Lead glass tubing in external diameters ranging from about 8 to 15 mm is most commonly used. The tube is usually melted into shape using small torches that run on a simple combination of natural gas (Butane or Propane work better, however natural gas is cheapest) and air.

An electrode is melted (or "welded") to each end of the tube as it is finished. The electrodes are also lead glass and contain a small metal shell with two wires protruding through the glass to which the sign wiring will later be attached. All welds and seals must be perfectly leak-proof before proceeding further.

The tube is attached to a manifold which is itself attached to a high-quality vacuum pump. The tube is then evacuated of air until it reaches near-vacuum. During evacuation, a high voltage is applied to the wires protruding from one electrode (in a process known as "bombarding") and the other electrode is attached to ground, allowing an arc to be struck through the interior of the tube. This arc heats the tube to a temperature just below its melting point, and any dirt and impurities within are drawn off in the gasified form by the vacuum pump. When completed properly, this process results in a very clean interior at a high vacuum.

While still attached to the manifold, the tube is now filled with one of the noble gases. Neon or argon are the most common; krypton, xenon, and helium are used by artists for special purposes. Neon glows bright orange red when lit with a high-voltage current. When argon is used, a droplet of mercury is added. Argon by itself is pale lavender blue when lit, and the droplet of mercury, which fills the tube with mercury vapor when sealed, then emits ultraviolet light upon electrification. This property allows finished argon-charged tubes to glow with a variety of bright colors when the tube has been coated on the interior with ultraviolet-sensitive phosphors before being bent into shape.

The finished glass pieces are illuminated by either a transformer or a switching power supply running at voltages ranging between 3,000 and 15,000 volts and between 30 and 120 mA. Neon signs are a type of cold cathode lighting.

Applications
The light-emitting tubes form colored lines with which a text can be written or a picture drawn, including various decorations, generally for use in advertising. By programming sequences of switching parts on and off there are many posibilities for dynamic light patterns that form animated images.

(Information courtesy of Wikipedia)