Thread: Yellow(ish) metals?

I have various pieces of brass, bronze and copper.
I'd like to be able to tell which is which, but being somewhat colour-blind I can't do it by sight.
Is there some other simple method?

Polish them up and take photos and post here. Cu will stand out like canine testicles, bronze/brass will be harder but we’ll will give it a crack. Annealed bronze will usually scratch annealed brass and less so the other way. Annealed pure Cu will be the softest.

If you have a strong magnet around, you should be able to pick the copper bits; not because it's magnetic, but because magnets do weird things on copper https://www.youtube.com/watch?v=sENgdSF8ppA

I've noticed on the bar stock at work that the bronze tends to have a darker "skin" on it than brass.

Originally Posted by elanjacobs

If you have a strong magnet around, you should be able to pick the copper bits; not because it's magnetic, but because magnets do weird things on copper https://www.youtube.com/watch?v=sENgdSF8ppA

I'm pretty sure that only works effectively on thicker pieces of copper and won't be so evident on thinner sheet.
Should work on rod though

If you have the same size tubes of materials a spherical magnet will fall slower though a copper one than a tube made of a bronze or brass.

Here are some chemical differentiation tests from the May 1930 "Popular Science Monthly" magazine, not only to test between bronze and brass , but between different types of bronzes and brasses.

https://books.google.com.au/books?id...e&q=92&f=false

Originally Posted by elanjacobs

If you have a strong magnet around, you should be able to pick the copper bits; not because it's magnetic, but because magnets do weird things on copper

https://www.youtube.com/watch?v=sENgdSF8ppA

I was aware of eddy current phenomena with aluminium but this is new to me with copper.

Originally Posted by BobL

Polish them up and take photos and post here.

Are the colours likely to be natural enough?
My phone-camera can do "correction" of photos automatically.

Originally Posted by BobL

Here are some chemical differentiation tests from the May 1930 "Popular Science Monthly" magazine, not only to test between bronze and brass , but between different types of bronzes and brasses.

https://books.google.com.au/books?id...e&q=92&f=false

This seems useful but still relies on good colour vision for some of the results.

The scratch test might be the simplest for me, to compare various pieces against each other.

Thanks mates.

Originally Posted by nadroj

Are the colours likely to be natural enough?
My phone-camera can do "correction" of photos automatically.

There’s no guarantee is would differentiate all samples I was just looking for a q&d soln. Photographing in sunlight will help. Cu should be easiest to identify but brass:and bronze will be harder.

If you have an accurate set of digital scale you could use the formula below to get a reasonably accurate identification of the metal pieces that you have, it should definitely show the difference between the copper and brass/bronze but may not be able to differentiate between the brass and bronze.

Density of Metals 3.pdf

Density of Metals.pdf

Originally Posted by Techo1

If you have an accurate set of digital scale you could use the formula below to get a reasonably accurate identification of the metal pieces that you have, it should definitely show the difference between the copper and brass/bronze but may not be able to differentiate between the brass and bronze.

Density of Metals 3.pdf

Density of Metals.pdf

Bronze is between 7.7 and 8.9, Brass is between about 8.4 and 8.7, and Cu is 8.96 g/cc

Weighing the pieces is the easy bit, the hard part is usually making accurate volume measurements as the OPs pieces are probably not all that regular.
At uni we use to give irregular shapes of these metals to the students in the lab to determine what they were and its much harder than it looks.
We also gave them a bunch of reasonably accurately turned cylinders of different brasses and some micrometers and a 4 place BALANCE and got them to see if they could work out what types of brass they were. The main emphasis of this exercise was to teach the stunes how to calculate final density tolerances from input measurement tolerances.

There is a very nice reasonably accurate way to more easily determine the volume of an irregular piece of material that is denser than water and that is using what is called a water displacement balance but there won't be too may people that will have the gear needed to do this.

The shape of the object is completely irrelevant when using the method that I posted.

Originally Posted by Techo1

The shape of the object is completely irrelevant when using the method that I posted.

That’s similar to the weight loss in water (wliw) method I referred to in my post.

Weighing something accurately with a sensitive balance while said something is suspended in water is not as easy as it seems.
To do this accurately requires a suspension jig of some kind which is easy enough make to make but is it worth it given the density ranges of bronze and brass overlap so much.

FWIW
Assuming the 144 is 144.0 in your calculation, you can't really claim 3 decimal places in the final result as the numerator and denominator only have one decimal place - your answer should thus be 8.4 g/cm^3
To get 3 decimal places in the final result the weights have to be measured to 3 decimal places.

There is also no need to weigh the water if the piece is also weighed out of the water as the difference between weighing the piece in and out of the water will be equivalent to the volume (V) of the piece.

At work we had an 4 decimal place balance with an hook attached direct to the balance weighing sensor underneath the balance. The hook was located over the top of a small hole in the bench. A wire attached to the hook held aa cage extended through the hole to a shelf underneath where a large tank of water was could be raised and lowered to submerge the piece.

One issue with this method this that smaller pieces have to be cut from larger pieces so they can be submerged in water otherwise a large tank of water and large and sensitive balance are needed. This may or may not suit the OP who may wish to retain the pieces whole.

To get really accurate results the buoyancy of the piece in air and the temperature of the water have to be taken into account.

As noted, this method gives approximate density, we used this method in identifying unknown samples at RMIT with good results. It has also helped me at work and at home so I continue to use it.

You get very different chips turning brass and bronze. Brass gives of almost dust like chips whereas bronze give of proper chips.