Spark plugs at progress:

Plugs have 3mm(0.118") holes through them, and 3.5mm(0.137") drilled for buttons at the business end. Above pic shows one button in place, that still has copper layer on one side. Some might guess already, that the material used for 'buttons' is fiberglass-based circuit board.
It stands heat, at least short periods at a time. I'm not sure, how porous it is under compression, but there is one way to find out

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One might wonder, why fiberglass; I have it already, it feels more solid, than ptfe, at the working end of the spark plug. It also has dielectric(insulativity) properties, that are needed at this stage.
Spark plug body, and center electrode, with one button, that has no more copper in it. White rod is ptfe, that is to be used to fill the rest of the spark plug's hole:

Center electrode is 1.4mm(0.055") steel, that will have an M1.4 thread at the end of it.
I'll make only one spark plug, to see if it works. Purely experimental, and not to be tried at home

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