Some company brought to the store a large advertising stand stating that the coating of their gas stoves could not be scratched, and immediately hung two samples of the material (normal, respectively,
and theirs, superhard) and near the metal rod.
One piece was all
scratched, the other, of course, did not take the metal rod in any way.
Putting the shield in the most conspicuous place, in the evening everyone dispersed,
there was only a guard.
The next morning, when the store opened, the advertisement was a fiasco: the shield stood still, but on the scratch-resistant coating, the artistically decorated shortest swear word flaunted in large letters, and next ... lay a diamond drill.