How neon signs are made

Bend over a ribbon burner

The bender marks the tube against a pattern laid out on a fire-resistant sheet, heats each spot in a propane flame, and bends it gently. Blowing into the open end restores the original diameter, and each bend is checked against the pattern.

about 30 seconds at 1200 F

Fuse on the electrodes

A hand torch melts an electrode onto each end. These are lead glass with a small metal shell and two wires running through. One end is sealed and the other stays open.

Add a side passage

A crossfire burner makes a small bubble of glass that opens into the unsealed electrode, the way in for the gas. Argon tubes get a drop of mercury here to brighten their light.

Pump and bombard

An end torch fuses the passage to a vacuum system. While the pump draws out the air, a bombarding transformer forces high current through the tube, which clears impurities.

15,000 to 25,000 V, 500 to 1000 mA

Fill with gas

A little gas goes in at low pressure, between 3 and 20 Torr. Clear tubing gives red with neon and steel blue with argon. Phosphor coatings inside the glass stretch that to many more colors.

3 to 20 Torr

Seal off the passage

The crossfire burner takes off the side passage and closes the electrode, trapping the gas. In argon tubes the mercury has to drop into the electrode first.

Black out the back

Stretches of tube that should stay dark get black paint, brushed even so the lettering stands out. One shop dips the whole back of the tube.

Burn in the tube

The finished tube burns for about 30 minutes at high voltage. That dries the paint and turns the liquid mercury into vapor that spreads through the whole length.

Mount and wire up

Clear clips hold the tube to a plexiglass backing, and its electrode wires connect to a transformer that steps wall current up to several thousand volts.