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Hi,

Question to the knowledgebase here. How can I tell the difference between stainless steel and aluminum? I'm trying to determine what I can just polish and what I need to take in for re anodizing.

This is actually for my ford project, but I figure that it is applicable to Packards too.

Thanks,

Mark

stainless steel is two and a half to three times denser than aluminum. The weight difference should be quite noticeable

Depending on the type of stainless, a magnet may stick to it. Aluminum, it will not.

If the part is aluminum and you polish it with Simichrome the paste will turn very dark . . . almost black. This discoloration will occur on the first, second, and twentieth time the part is polished, and is a result of a chemical reaction between the aluminum and the ammonia in Simichrome. Stainless may darken the paste the first time, but that effect diminishes as the part's surface is cleaned. Once the surface of the stainless is clean the paste will remain pink.

Some anodized also has a clear lacquer like coating to help resist corrosion that stainless does not.

Magnetic property is not definitive as some stainless steels are magnetic, others are not. Nor is the presence or absence of a lacquer coating necessarily definitive. As Bkazmer has stated, the most obvious difference is weight. Another is lustre. And a 3rd can be surface hardness; the aluminum used for auto trim is softer that the stainless - test with a file on the backside vs a couple of known samples.

Thanks!

...am I also remembering correctly? If i take a grinder (i have spare pieces of trim)...stainless gives a dull red spark and aluminum gives off no spark?

I would check the parts documentation first.
Since you don't want to do destructive tests; mostly visual,
If there's whitish powdery solids on it in areas of corrosion, it's most likely aluminum. Stainless tends to rust stain or get a film.
The stainless will most likely stay brighter longer, so if it's maintaining its shine, it's probably stainless. The thickness may also be a clue. The aluminum would be a gauge or two slightly thicker. Aluminum is a bit softer, so a pin prick or scratch on the back side. Stainless will resist.

You can usually just tell by eye and feel, and how its made, but that takes experience. The stainless would likely be used in smaller accent trim pieces, and the aluminum in larger, like grills, wide splash panels. But depends a lot on the vintage which is not given. And cast vs rolled. If it's cast, its most likely not stainless, but could be other non-ferrous alloys. You can polish on the back/non-showing side and see how it goes.

Aluminum will react to dilute sulfuric and stainless won't but that's destructive, if you don't wash it off right away.
Similarly with caustic but it's much more potent and reactive, potentially explosive - not recommended here.