Ball trough, balls, any area the balls go that you didn't clean.

LTG : )™

I was told that whenever 2 bits of metal make contact, you get dust/dirt.
You'll find that it coats pretty much everything under the playfield.
That includes the ball trough as LTG said.
The balls then track all the dirt all over the playfield for you to enjoy.

The coil plungers hitting the coil stops make that black, pulverized metal dust that covers everything.

The heat and no fan w/in a cabinet of a typical pinball machine generates this sort of stuff. Best bet to keep the ball trough clean and a wipe w/Novus 2 or 1 from time to time. I have a re-import BSD and no matter what I do, I still get dirt due it's early Euro lifestyle of cigarettes and beer.

You need to keep in mind that TSPP has a light colored playfield. There are different colored TSPP playfields, but from your pics, yours looks very bright. I'd guess it's not a first run playfield. Ball trails will show up quick on light colored playfields. No way to avoid that. POTC is another one.

And even on a brand new game, dirt happens. You can't clean all the dirt away because it will come right back. Even HEP games get ball trails. White rubbers and bright post sleeves (neither are factory) are magnets for dirt, as are urethane flipper rubbers. It's somewhat ironic that bling attracts dirt. You wanna look good, you gotta get dirty.

I operated my TSPP and whenever I had the glass off, I cleaned the upper playfield. A dirty upper playfield eventually makes the couch shot impossible. I also kept the upper flipper rubbers clean (along with the 3 lower flipper rubbers). The rest of the rubber rings occasionally got cleaned. Lower playfield got cleaned after the upper and not as meticulously. Keep your upper playfield clean and don't sweat small ball trails and smudged posts on the lower playfield. It's an epic game that takes many hours to explore. Don't waste too much time cleaning.

Flippers are about how many flips instead of how many games. 800k-1mil flips for it to mushroom like that and maybe 100 flips to start to build up the dirt on a new rebuild

Every coil with a plunger and a coil stop is a culprit, not just that one.

Looks like you are long overdue for a rebuild.

I recently added a tspp to my collection and have noticed the same thing, more so than my other machines. I also did a thorough tear down and clean and the black dust keeps returning. I think the poster above is probably right, that it's due to the light color of the PF. It's just more noticeable.

Jack

When cleaning metal parts and re-graining guides I wipe them off with with isopropyl alcohol to get any residue left. You can also do this with the balls before reinstalling them.

Clean in pinball is just a moment in time.