Bronze or Copper?

[lesweeks]

Am I the only one who finds it difficult to tell copper from bronze? I've got some old fastenings of a good diameter (3/8") from where I've replaced part of the stempost and the breasthook. I'd like to turn them down and use them for the spindles in some old wooden blocks I'm restoring with new tufnol sheeves - bronze would be good, but copper not. Is there an easy way to tell them apart 'in the rough'?

 

[fishermantwo]

If you have old bits off an old boat its likely to be bronze or gun metal. Hard to tell otherwise, I think bronze is a bit more gold colour and brass a lighter yellow. I save all my old stuff off my fishing vessel which was built during WW2.

 

[old_salt]

Not an easy one to explain in simple terms.
There are quite a lot of different specifications of Copper, Brass, Bronze and silicon Bronze.
Far to detailed to go into here.
Generally copper is soft there is harder copper and just the same with bronze.
So a very simple rule of thumb is Copper will scratch bend easer than Bronze.
The colours are a guide but that tends to come with practise.

To give you some idea have a look here.

 

[burgundyben]

It can be tricky, and as Old Salt says its complex as there are so many different alloys.

A excellent background book is http://www.amazon.co.uk/Metal-Corrosion-...7316&sr=8-1

 

[cliffordpope]

If it's pure copper it will surely be definitely reddish brown, like boat nails? Bronze is more yellow, but not as brash a yellow as brass, which looks, well, brassy.
In my observation bronze seems to have a courser, chunkier kind of grain than brass, sometimes with small casting bubbles. Brass always looks a bit too good to be true.

Of course if it's corroded by salt water then brass will be crumbling to pieces with dezincification.

 

[monkey_trousers]

someone once told me, although I've never tried it myself, drop or 2 of good malt vinegar and leave it an hour

bright green verdigris colour then its copper

paler green and the metal under neath goes a salmony pink then brass or bronze

 

[Peterduck]

I am puzzled by your assertion that bronze would be good for the sheave pins, but copper would not. Why not? Copper is very close to mild steel in strength, so I think that it would be quite adequate in that respect. I am sure that copper pins would last for your ownership of the boat, if not your lifetime.
Peter.

 

[NobbyMan]

A good method to tell the difference is to run a file over the surface, copper will catch more being softer.

 

[jimbaerselman]

[ QUOTE ]
Copper is very close to mild steel in strength,

[/ QUOTE ] Forgive me, but I think you're wrong here. Bronze (the tin alloy of copper) is nearly as strong and stiff as steel, and is good for making springs, bells etc since it will resonate when struck. It's an excellent bearing surface . . .

Copper (of reasonable purity) is soft and ductile - the plumber's favourite - and is so soft that it will not resonate when struck, is easily bent and scratched with iron, and once bent will hold its new shape. Not good as a bearing pin, since it would rapidly wear away.

Brass, the zinc alloy of copper, is strong, but suffers internal electrolysis when immersed in seawater (de-zincifies).

There are, of course, a number of other copper alloys (including phosphor, silicon, aluminium as well as zinc or tin) which are usually generically known as bronze . . . they're all strong, hard and resonant. Can be stratched with iron, but not easily . . .

 

[fishermantwo]

[ QUOTE ]

Copper (of reasonable purity) is soft and ductile - the plumber's favourite - and is so soft that it will not resonate when struck, is easily bent and scratched with iron, and once bent will hold its new shape. Not good as a bearing pin, since it would rapidly wear away.



[/ QUOTE ]

Because Les is planning on turning down some material he has removed from his boat there is a good chance its Bronze or gun metal. Unlikely to be copper.

 

[jimbaerselman]

Agreed. I was just responding to Peterduck's comment about copper strength. Of course, lots of caveats (unstated) about how the material was formed (drawn, rolled, annealed etc).

 

[lesweeks]

Having put it on the lathe it is certainly copper. One of a pair, originally 3/8" dia and 6" long, riveted over both ends to secure the breasthook. Very soft - dragged badly off the tool tip until I stopped being lazy and re-ground it. I'm sure I'll find a good use for it at some stage, but I'm not going to use it for block spindles. I think the posts above show that it's not always easy to tell by looking; a touch with a file seems to be as good as any way. Thanks everyone.

 

[burgundyben]

[ QUOTE ]
a touch with a file seems to be as good as any way.

[/ QUOTE ]

Indeed.

I really cant reccomend enough the book I linked to further up. Its a valuable minefield of information on all the different types of copper based alloys (brasses and bronzes) and their properties.