The scratch-and-win specialist marks the keys with printed codes and covers them with a special scratch-off layer (thermochromatic or other security inks could be used).
In contrast to the jet technology the inks do not penetrate the structure paper, but they are brought to its surface and are covered with special fixing agent for shaping of thin film.
The recent discovery of a pterosaur specimen covered in long, dense, and relatively thick hairlike fossil material was the first clear evidence that his reasoning was correct.
All paper products on the assembly line are covered in plastic to make certain that even the small fibers that might break away from the pages can't escape into the air.