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Identifying brass?

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Peter Howell 114/03/2021 15:16:18
33 forum posts
4 photos

I've been give an old boat propeller shaft. It looks to be a very useable piece of bar.

How can I identify if it is brass or bronze. A quick 'Google' shows boat prop shafts have been made from both. (Now nearly all are stainless). Colour wise it looks like brass.

Bo'sun14/03/2021 16:52:25
514 forum posts
2 photos

Can you compare it with another piece of brass. Cleaned up of course. There are a number different grades of brass which may vary in colour slightly, but it might be a good start. I've not got any, or used any bronze for years, but if memory serves, it has a slightly "coppery" colour compared to brass.

I'm sure there are more definitive ways, but I'd go the simple route to start with.

Another thought. Bronze might be the material of choice for salt water corrosion resistance. Hence being used for a prop shaft.

Grindstone Cowboy14/03/2021 17:05:18
707 forum posts
58 photos

Does bronze de-zincify the same as brass? If it doesn't, could you try heating a sample and seeing if it turns pink?


old mart14/03/2021 17:23:03
3337 forum posts
208 photos

Bronze does not contain zinc so it is better able to withstand the corrosive affects of sea water. I was surprised to hear that a propellor shaft would be made out of a copper alloy, most likely bronze of some sort, they tend to have a more coppery colour than brass.

Clive Brown 114/03/2021 17:55:58
702 forum posts
33 photos

In marine useage, the terms brass and bronze can be rather vague. A propellor shaft could well be naval or admiralty brass which can also be called tobin bronze, although it contains very little tin. Items referred to as bronze could well be an aluminium bronze, common for propellors, or manganese bronze.

All of these materials are strong and highly resistant to sea-water corrosion.

noel shelley14/03/2021 19:24:08
754 forum posts
19 photos

Bo'son has beat me to it ! For salt water a Cu/Sn alloy would be prefered but some bronze does have Zn in it. The Cu alloys are a vast subject. A pale colour can indicate Cu/Sn but only a true analysis of a sample will tell you for sure, But this is model making, will it make any significant difference ? Noel.

Hopper14/03/2021 21:00:45
5505 forum posts
137 photos

I have a prop shaft someone gave me, a lovely piece of yellow metal 1" diamter and five foot long. Looks nice and yellow like brass. But try to hacksaw a piece off and then machine it in the lathe and it is tough as anything so I have always assumed it's bronze of some sort. Definitely does not cut like nice soft brass.

As Noel says, it doesn't make any difference. I use it for general purpose work where either metal would do the job.

Nigel Graham 214/03/2021 21:34:06
1704 forum posts
20 photos

That "lovely piece of yellow metal" that isn't lovely to machine...

Yellow but somewhat paler than ordinary brass? It might be aluminium-bronze, used in marine engineering for its excellent corrosion resistance.

It isn't lovely to solder, either, as I found when tried to make a locomotive fitting from an oddment of it.

SillyOldDuffer14/03/2021 21:56:15
7544 forum posts
1679 photos

There's a simple chemical test for Tin described here.

Although the chemicals are available (Patio cleaner is Hydrochloric Acid, Zinc from Batteries and Potassium Permanganate from a Chemists), many of these old chemical tests require 'laboratory technique' and experience. Worth practising on lead-free electrical solder which is almost pure Tin to be sure the blue fluorescence is recognised.

If Tin is detected the metal is probably a Bronze. There is a fly in the ointment because a propeller is probably made of Admiralty Brass, which is 1% tin, less than a true Bronze (at least 10%), but maybe enough to confuse the test.

Of all the alloys, Brasses probably have the widest range of properties. Brasses with a high percentage of Zinc are so soft and crumbly as to be useless, whereas at the other end of the scale it's hard and tough, with pretty much everything in between. A dash of lead makes it machinable, Aluminium makes it stronger, and Iron harder and so forth. Cartridge Brass is malleable, others are good for forging, casting or rolling. Brass is my favourite metal, but some of it a pig, I'm not sure how useful the Brass in a second-hand propeller will be, but give it a try.


Hopper15/03/2021 01:04:27
5505 forum posts
137 photos
Posted by Nigel Graham 2 on 14/03/2021 21:34:06:

That "lovely piece of yellow metal" that isn't lovely to machine...

Yellow but somewhat paler than ordinary brass? It might be aluminium-bronze, used in marine engineering for its excellent corrosion resistance.

It isn't lovely to solder, either, as I found when tried to make a locomotive fitting from an oddment of it.

Yes that sounds like it exactly. Thanks for the soldering tip. I shall avoid that.

Circlip15/03/2021 08:32:07
1353 forum posts

"That lovely piece of yellow metal"

Check it with a magnet, slightly magnetic? Alluminium Bronze.

Regards Ian.

Hopper15/03/2021 09:19:34
5505 forum posts
137 photos
Posted by Circlip on 15/03/2021 08:32:07:

"That lovely piece of yellow metal"

Check it with a magnet, slightly magnetic? Alluminium Bronze.

Regards Ian.

That sounds so bizarre I had to go out in the shed an check it. Sure enough. It's very, very slightly magnetic. Not enough for a magnet to stick to it when put together by hand, but enough to move a strong magnet hung on a string when the bronze prop shaft is brought within about 5mm of it. It swings right over and sticks to the bronze. Amazing. Turns out aluminium bronze contains a little bit of iron too, Dr Google tells me. Thanks for the tip. Good to confirm what I had suspected that it is bronze and not brass.

Edited By Hopper on 15/03/2021 09:20:16

Nigel McBurney 115/03/2021 09:32:49
918 forum posts
3 photos

An friend who worked for a company that did a lot of work machining bronze and got me a lot of off cuts,once told me that one way of identifying bronze/brass was that brass can be annealed ,bronze cannot be annealed, I did try annealing a piece of bronze and it would not anneal like brass or copper does,though I do not know if this applies to all type of bronze. Aluminium bronze is slightly magnetic,our local scrap merchant keeps a magnet handy for testing.

noel shelley15/03/2021 10:07:30
754 forum posts
19 photos

I like to learn something new every day !

Magnetic bronze and it can't be annealed !

Todays objective has been achieved - I can go back to bed, until tomorrow ! Many thanks all, Noel.

Michael Gilligan15/03/2021 10:24:00
18921 forum posts
941 photos

My go to reference for all things coppery is

To demonstrate ...Here’s a search for ‘magnetic’ : **LINK**


Russell Eberhardt15/03/2021 10:32:24
2703 forum posts
86 photos

If it came from a sea going vessel it would not be brass or Admiralty brass. Neither is suitable for continuous immersion in sea water due to the high proportion of zinc. Zinc is used for sacrificial anodes to prevent corrosion of other metals in sea water. You should see what they look like after a couple of years at sea§*!


Peter Howell 115/03/2021 11:36:23
33 forum posts
4 photos

Thanks for the replys. Yes its bronze.

So is it going to be any use to me? It's about 1" dia.

JasonB15/03/2021 11:45:27
21431 forum posts
2448 photos
1 articles

There has been some nice work done using old prop shafts such as the "Golden No1"

Build details here

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