Neon signs are made of glass tubes bent to form letters or shapes and then filled with inert gas. Once the electric current hits the electrodes in the glass tubes, the electrons will flow through the gas, making its atoms glow. The color of light in the neon signs is determined by the type of gas and glass.
In a clear glass tube, argon gas gives off blue light while neon gas gives off red light. If you want to create vivid designs, you can parlay those two base colors into more than 80 additional colors by using glass tubes colored with fluorescent powders, for example, blue glowing gas in a yellow tube will produce a green light. A glassblowing technique is used in shaping the tube. Following a pattern drawn on a fire-resistant sheet, they mark where they have to bend the tube. Each spot is then heated on a device called a ribbon burner whose propane flame is a blazing 650 degrees Celsius. The glass softens enough within half a minute to be pliable. They gently bend this tube and then blow into the uncorked end to restore the tube’s original diameter.
The shape is checked with each bend against the pattern, often pressing a wooden block along the tube to equalize the width. Argon gas produces steel blue light. But the blue color tube changes that to dark blue.