Identifying a metal

[Rat]

I thought I'd asked this before, but if so, I can't remember the response.

How do I go about identifying the metal from which something is made? Wholly destructive testing is not an option, but scratching it or disfiguring a small portion is not a problem. I have an ashtray (actually it belongs to my better half, but she rarely smokes), and I can't quite identify what it's made of. It looks sort of bronzish, and tarnishes similarly, but I'm not sure. To start with, it is sort of shiny off-gold coloured when scratched (I'm colour-blind, so tints may pass me by), and tarnishes to a very dark brown colour (I think). Unlike, say, a British penny, which I believe is cupro-nickel, it does not become cleaner on exposure to vinegar. Indeed, as far as I can tell, vinegar makes very little difference to the tarnish.

What tests can I put it to that would lead me to a definitive answer? Household chemicals only are available, btw, so no exotic acids or anything else can easily be used.

Cheers,
Rat.

[Mr. Skinny]

I thought I'd asked this before, but if so, I can't remember the response.

How do I go about identifying the metal from which something is made? Wholly destructive testing is not an option, but scratching it or disfiguring a small portion is not a problem. I have an ashtray (actually it belongs to my better half, but she rarely smokes), and I can't quite identify what it's made of. It looks sort of bronzish, and tarnishes similarly, but I'm not sure. To start with, it is sort of shiny off-gold coloured when scratched (I'm colour-blind, so tints may pass me by), and tarnishes to a very dark brown colour (I think). Unlike, say, a British penny, which I believe is cupro-nickel, it does not become cleaner on exposure to vinegar. Indeed, as far as I can tell, vinegar makes very little difference to the tarnish.

What tests can I put it to that would lead me to a definitive answer? Household chemicals only are available, btw, so no exotic acids or anything else can easily be used.

Cheers,
Rat.
Well, you could send me a sample and I'd see what I could do. I'll PM you.

[patnray]

You could measure the density and compare that to the density of common alloys. You'd have to be able to accurately measure the mass and volume...

[NobbyNobbs]

You could measure the density and compare that to the density of common alloys. You'd have to be able to accurately measure the mass and volume...

That's easy enough. For mass, get a scale. For volume, dunk it in water and see how much it displaces.

This method will work, but only if the entire ashtray is made of one type of substance. If it is metal with a ceramic core, or a glass inlay, this won't work.

[Rat]

I can see that I can work out density by weighing vs water displacement, but I don't have anything like the equipment to judge either of those to any great accuracy. I have the impression that people who have worked with metals would be able to pick it up and say "oh yes, that's...", but I've only worked extensively with steel, and I can say with certainty that it's not that. I'm pretty sure that it's solid whatever-it-is, and that it's not valuable.

It's really only curiosity that drives me to wonder. I can normally identify metals from properties and context; that is, what it looks like, and what it's being used for. But this looks very much like bronze, but doesn't behave like it. And I can't imagine why you would make an ashtray (assuming that's what its original purpose was) out of bronze anyway.

To either confirm or deny my original instinct, is there any easy way to identify bronze?

Cheers,
Rat.

[chance]

What about a process of elimination using harder and softer metals/materials that you know for certain are? E.g. Copper should be softer Steel is harder etc.
Find a chart of relative harnesses.
You might be able to eliminate if not confirm.

[casebro]

Google for "metal assay" ? I'd say bronze. But the bronze/brass family has lots of alloys. Bronze and brass can both have tin and zinc in varying amounts.

I know they use a machine that makes a certain type of electromagnetism. Looks like a voltmeter with a pad on it. The 'conductivity' of magnetism and electricity tell lots about the metal. I had one but sold it before using it. Made by the Magna-Flux company. Perhaps a scap dealer would have one of the gismos?

[Amapola]

Here's a website for identifying many types of materials, not just metals. My guess would be pewter...... it contains lead so see if you can make a mark on a piece of paper with your metal. Identifying various materials (http://www.buttonimages.com/collector_info/identify.htm).

There are indeed lots of alloys that are sort of bronze-like, so they can be tough. Here is an article about bronze - dealing with sleigh bells, but it should have some good info for you: Brass and bronze bells (http://classicbells.com/Info/BrassBronze/BrassBronze.htm).

I do have an old ashtray that was made right after WWII. It really is brass, so they do make them from brass. Mine is in the shape of a cowboy hat, and I use it for a business card holder. But if yours does not act like brass or bronze, I would think it was pewter.

[CaveDave]

... Bronze and brass can both have tin and zinc in varying amounts...

Also, there is aluminum bronze, leaded brass or bronze, and many other mixtures.
Silicon, arsenic, phosphorus, calcium, and other metals may be added to modify the properties.

At the nonferrous foundry where I used to work, we used a very expensive testing machine which identified alloys by their spectra. A sample was machined clean and flat, loaded against a vacuum chamber, and subjected to an arc from a carbon rod to the sample. The light from the arc was then analysed by a difraction grating and the important spectral lines measured by photomultiplier tubes. A minicomputer then did data reduction and curve fitting to print out the sample's analysis.

Many brass/bronze articles (bells, censers, candleholders, trays, dishes, etc.) are cast then turned/spun and exported from India/Pakistan/Bangaledesh/Afganistan/other eastern countries and may have widely varying analyses depending on what is locally available (scrap) for them to alloy.

HTH

Cheers,
Dave