Earlier quoted context omitted.
No cover, just straight up gorilla glass victus. And it's not just key metal deposited on the screen, there are deep grooves cut into it.
I believe you, but there is some other explanation here- it warrants further investigation. You can scrape a regular glass window (about MOHS 6.5) clean with a razor blade (about MOHS 6.0) and it is impossible to scratch it, just from that tiny difference in hardness. I do this all the time, e.g. recently to get paint that my kid painted on the house windows off. Your brass keys should only be about 3.0, and gorilla…
Typical keys are made from nickel plated hardened steel and nickelsilver. Considering the shiny coating is long gone and the keys are ferromagnetic, I assume it's the first. The keys are certainly hard enough to scrape my glass ceramic stove.
And reports online say that gorilla glass victus is the mist scratch prone gorilla glass, scratching at or around 6 already :/