#patterntale

Sans are a type of copper. The blue side is oxidized.

Gaster used copper because it conducts electricity

Pap has copper too but it's more a mishmash of conductable elements and his copper parts are waxed so it doesn't oxidize.

Pap does ultimately learn the truth (sorta), but is less upset and waaaay more concerned. There's a lot he'll never learn and the only reason he's able to find the last important bits of info is because of Frisk. He does figure out that Gaster was not a good person. Though it sends him into a sort of spiral.

Ofc, learning you were supposed to be the ultimate perfect copy of another person isn't exactly easy.

He loves his brother unconditionally and so when he finds out about Sans's soul he's incredibly torn between his ambitions to be in the Royal guard, his loyalty to the soul hunters and his love towards his brother who basically raised him. He doesn't take it easy and pretty much breaks down because he doesn't know what to do. Though I'm not entirely sure at this point this is the current concept.

Also

Pap has spoken to an apperation of Gaster multiple times. So that's a bit of a shocker too