piston coating?

[V8Bart]

Just started cleaning up old pistons, some original tvr 5ltr some newer but same spec.

Using oven cleaner on originals was fine but new ones seems to have reacted to a coating and stripped it in places, leaving a darker, duller surface. Like blistering.

Is there a coating on them? Would a recoat be possible ? Expensive?

[Sardonicus]

I strongly recommend you don't use caustic based/sodium hydroxide/lye cleaners on aluminum components at the least it will discolor the aluminum at worst it will eat and pit the material permanently