There we have it then.
It is in just the surface of the metal, I believe, but it should be very durable.
I just went and stuck a fork over the hob, waited till it was red hot, put it under the tap to get it heat discloured and then ground into it with a dremel - it doesnt go all the way through, but its pretty resilient.
Disclaimer - different materials, not sure its the same for both, but its probably the same mechanism.
Cue someone coming along and saying their burnt chrome cover got scratches in 10 minutes :lol: