What is that and what has it done with my spark plug?

[dauchande]

I was changing the valve cover gaskets, spark plugs and boots and when it came time to change spark plug #1 (or is it 4..), I see this

It's some kind of covering over the spark plug that covers the hex cuts for the socket. It is white (although it's hard to see from the pic) and metallic sounding when I tap it with a screwdriver.

Please tell me this is not someone's idea of a cheap fix for a stripped spark plug well.