Spark arrestors are nothing more than a thing built to stop hot carbon or metal from being able to fly out of your pipes and catch something on fire. They are normally made of a screen mesh or many screens and some sort of insert. It's all bullshit, just another requirement the tree hugger where able to get the government to buy off on, because those "possible" stray carbon fragment might catch something on fire, while those bottle rockets, fireworks, and 20 foot race fuel induced bonfires are safe.
As for the polishing, I think he sent them to Kiel (theshee)