I'm going out shopping at thrift stores, how to tell the difference since it won't be on the package?
Bring a magnet along with you, it will stick to a stainless steel one and won't stick to an aluminum one. Aluminum is lighter weight too.
The magnet is a good idea... although aluminum is a metal, it doesn't contain iron (like steel or cast iron pans, etc.) so a magnet won't stick to it. It's a common misconception though that magnets will stick to any metal. Try putting a magnet on various pots (and metal baking pans, etc) you already have, or even aluminum foil, to see. Some more expensive stainless steel pans will be steel sandwiched on both sides of an aluminum layer, but the magnet should stick because of the steel.
No, aluminum isn't magnetic, but all stainless pots are not magnetic. Most of them, maybe, but not all. Look on the bottom of the pot, it might say what metal it is. A number like 18/10 or 14/10 means stainless. Aluminum is almost always a dull silver colour, very rarely shiny. It's much softer than stainless and will scratch and pit much more easily. If the pot has any pitting inside, it's very likely aluminum. If it has any dark discolouration, it's aluminum. If in doubt, don't buy it.
