Letter 42044

What is the mechanism for the different characteristic odors of metals when handled? [Canada] 

August 25, 2006

I design and test military sensor and communication gear, in which esoteric materials and finishes are used that no sane commercial designer would entertain, so the question of "What's this made of?" often comes up.

One of the ways I use to distinguish metals, platings and conversion coatings is by the characteristic smell each gives off when handled.

I've been using this technique for years, but have never been able to find out what the underlying mechanism is. A friend doing graduate work in inorganic chemistry asked everyone he could think of at the University of Calgary, and still no answers, so I present it to the forum.

The vapor pressure of most metals and oxides is insignificantly low, meaning I don't think it's the base metal or oxide we're picking up, so what's happening to produce that characteristic smell? It seems to have something to do with the reactivity of the metal, because gold and chromium are much fainter than others.

If you haven't tried it, by the way, pick up a sample of metal, rub it with your thumb and then take a slow sniff. Compare it to other samples of known composition to help identify the material. With a bit of practice you'll be able to tell that bronze is a mix of copper and tin, that stainless is steel with chromium and a bit of nickel, and so on.

I've got no specific application for this question, it's just an annoying hole in my understanding of what I'm working with.

Ulrich Hissen
- Calgary, Alberta, Canada

Ulrich,
It too have observed this effect, most particularly with iron and zinc. I have wondered if it was a reaction product with finger sweat, though I am not so sure as zinc smells to me even if its not handled. Maybe a little reserch project for some one with a good Gas chromatograph and some spare time!
Thanks,

John Sherborne
- Guildford

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