I had this happen today and figured I can't be the ONLY person in the world to get confused. I'd done a "quick sort" and had a barrel of what I thought to be Stainless Steel turn out to be some brass that was chrome-plated and one piece of aluminum. What confused me was not thinking that faucets are likely brass; not stainless steel (the tub or sinks will perhaps be stainless steel). So, this is the "procedure" I came up with:
(This applies only to those "shiny" pieces).
First- Is it magnetic? If it is, It's probably Stainless Steel (or chrome plated steel). If not; it could still be Stainless, but might be Aluminum or Chrome-plated Brass. Second - Test with a grinder - sparks means Stainless Steel. No sparks means Aluminum or Chrome-plated Brass. Third - Use the grinder to grind off a section - if it stays silvery, it's Aluminum. If it's more yellow or gold colored, it's Brass.
A lot of times, pots and pans will be marked on the underside - "Stainless Steel" or "Aluminum". Another thing is to consider the object's use. If it's used around high heat, it is more likely Aluminum (ie: heat sink, motors). If it's used around water, it's likely copper (as in lines) or brass (as in faucets or valves).
Stainless Steel is made using Chromium (chrome), so if it's true Stainless, it will have a uniform appearance throughout. Cut or grind through the piece of metal to make sure it's not just chrome-plated steel.
Check with your yard regarding how to separate various grades of Stainless Steel. My yard has me throw any magnetic stainless steel with #1 iron.
Please feel free to correct or dispute any of this as it's just what I came up with.