Brass and bronze

[PH]

I have a box of brass/bronze bits - offcuts, salvage etc.
Is there a reliable way to distinguish between the brass and the bronze? I don't fancy spending time making a bush or a rubbing plate to have it disappear in a matter of minutes

[abby]

brass is yellow , bronze has a reddish hue except for aluminium bronze which is yellow buy has a slight magnetic pull.
Abby.

[houstonceng]

PH

Don't want to be an angel of doom but - - - - -

The only fully reliable way is chemical analysis. "Bronze", "Brass" (Navel or "Cooking" variety) and "Gunmetal" are near interchangable terms from some people.

There are so many additives such as lead, phosphorus & nickel that can be added to the basic Copper/Zinc (Brass) or Copper/Tin (Bronze) alloys, which will alter their colour and properties (eg look at "German Silver"). Notwithstanding the additives, the actual proportions of Copper, Zinc or Tin in the alloy can have dramatic effects of the properties.

If you are going to use some "yellow metal" for a specific duty (say boiler bushes or a heavily loaded bearing), I'd advise buying a known variety and not chancing to luck. Look what happended to Fred Dibnah's traction engine front wheel bearings that he made from "some unknown stuff from the breaker's yard".

Regards

[abby]

Whilst I agree entirely with houstonceng's post regarding the derivitives of copper alloys and terminology - in the states they have "red brass" can you believe ? which we in the UK would call bronze , I still think " if it's yellow then its brass" and will suffice for any duty where brass is called for. If you are having difficulty turning or silver soldering check it with a magnet , it's most likely aluminium bronze ! A piece of phosphor bronze bar looks nothing like a piece of brass bar , and because of the large price difference most scrap dealers are well able to sort brasses and bronzes. We are making models at the end of the day , not nuclear power plants.
Just my opinion of course LOL !
Abby.

[JohnP]

Well I'm going to risk the combined scorn of the group here.

Brass can be magnetic.

There, I've said it. I suppose you want proof.
In my day job I'm involved with equipment that is used to determine the direction that the holes go when drilling for oil. As part of that I've been involved in calibration of the sensors that detect the direction of the Earth's magnetic field (flux gates). When you work with these you have to empty your pockets and take your belt off, simply because the magnetic effects of coins (honest - try a new 2p piece with a magnet), buckles etc. We had trouble with spurious effect which were traced to some supposedly non-magnetic brass. The effect was such that the pull could just be detected using a Samarium Cobalt magnet (they are strong).

I know copper and zinc are non mag, so it must have been down to impurities in the mix.

And no, there weren't any broken taps buried in a blind hole!

So it all goes to support houstonceng's point about chemical analysis.

JohnP

[Myford Matt]

New copper coins such as the 2p are magnetic because they are 'Copper-plated steel', as described by the mint.

Problem was, the copper was worth more than the coin.

[Myford Matt]

Saw this lot on another website (ie not my own words) - quite interesting:

Newsgroups: rec.crafts.metalworking
Subject: Re: Brass vs. Bronze
Date: Tue, 29 Jun 1999 14:11:13 GMT

Using just copper/tin as a definition of bronze is fairly pointless and not generally recognised as being either useful or correct for many years now. Current definitions are that copper/zinc based materials are still called brass and other copper based alloys are called bronze regardless of tin content.

From the Handbook of Chemistry and Physics (but not a current edition)

90% Cu 10% Zn known as commercial bronze (also as red brass)
89% Cu 9% Zn 2% Pb hardware bronze

Both nickel and cobalt are common constituents of copper based alloys and both elements are ferro-magnetic. Not surprisingly, alloys containing these can have magnetic properties.

Actually all materials have [some] magnetic properties. In fact the Ross materials handbook lists copper based alloys designed "FOR USE AS MAGNETS" !!

e.g. "Permet" - 21% Ni, 29% Co, Cu remainder
"Magnetoflex" - 20% Ni, Cu remainder - strip for magnets.

I could go on.

So many copper based alloys will just be attracted to a magnet and others will even have magnetic properties of their own. There is also a wide range of sintered materials having a coppery appearance and used for such things as bushings, engine valve seats etc. For many years I was convinced from the appearance that a particular engine I regularly saw had bronze exhaust valve seat inserts. It is only recently and by accident that I noticed shavings sticking to a magnetic screwdriver and now suspect that the material is an iron based sintered material with high copper content.

However it is [usually] only with significant additions of either iron, nickel or cobalt that a copper based alloy can be either magnetic or attracted to a magnet. In such case a "true" bronze - i.e. primarily copper/tin will not have those properties.

The addition of iron, nickel, or cobalt is common but is not necessary to get a copper based magnet. [An exception is] 61% Cu 26% Mn 13% Al is an interesting magnet in that it does not contain either iron, nickel or cobalt.

Where you draw the line on what is and is not bronze is more a matter of semantics than engineering.

[havoc]

Current definitions are that copper/zinc based materials are still called brass and other copper based alloys are called bronze regardless of tin content.

From the Handbook of Chemistry and Physics (but not a current edition)

90% Cu 10% Zn known as commercial bronze (also as red brass)
89% Cu 9% Zn 2% Pb hardware bronze

Since Zn is Zinc and Sn is Tin, both of the above should be brasses...