Before you touch any piece with sandpaper, grab a magnet. Aluminum and brass: Won't stick, they're non-ferrous. Stainless: Depends on the grade, some stick, some barely do. Here's the one that matters most: if a piece looks mirror-bright already and you're not sure what it is, assume it could be chrome plating over steel until proven otherwise. Why it matters: chrome is a coating a few thousandths of an inch thick. Sand through it and no compound on earth brings it back. That piece needs re-plating, not more polishing. A two-second magnet check plus a close look at the plating condition has saved more pieces than any technique I know. What's your pre-sanding check routine? Drop it below 👇