Each key on a keyboard bears a legend identifying the letter, symbol, or function it activates. These legends are usually applied using one of three technologies:
Double-shot keycaps have the legend molded in.
Making each keycap is a two-step process. Black plastic is molded into the inner shape of the keycap that attaches to the switch mechanism. The legend protrudes from the top of this inner cap. Then light plastic is molded over and around the inner cap with the legend showing through the top.
Using the double-shot technique, each keycap for each key is a separate and different part that must be individually installed in the correct position on the keyboard as the final step in the production process. Assembly is complex, and stock-keeping of parts and completed keyboards can be costly. Although once popular, this technology has fallen from favor.
Pad-printed keycaps have their legends stamped into place.
A machine inks on the legends on all the keys on a fully manufactured keyboard at one swoop. Then a transparent protective layer is applied over the ink and is baked to a permanent finish. Notebook computers and keyboards with light legends over dark caps often have their keys pad-printed. In the case of notebooks, the assembled keyboard gets baked before the keyboard is installed on the computer.
Laser-marked keycaps have their legends burned into place with a laser.
The process is akin to a laser printer that operates on keycaps rather than plastic. The complete keyboard is put into a big machine with a laser and mirrors, and the laser burns the legends into all the keycaps in one operation. The advantage of the process is that the legends only need to be applied at the last moment, right before the keyboard is shipped out with a new computer, and the language and layout of the keyboard need not be set until then. The process is fast, the legends are long lived, and stock-keeping is simplified. Most new keyboards are now laser-marked.