Differentiating Copper from Brass for the colour blind *Solved*

[Robert Clarke]

Hi All,
Would anyone have any ideas of a simple and fairly non-destructive method to identify brass? One idea I had was some chemical that will react with the zinc but not effect copper?
All the methods I can find rely on the colour difference of the metals but unfortunately for me I ain't got that chromosome.
Thanks folks

[Robert Clarke]

I may have hit on a solution already. And its reasonably simple if the physical circumstances are right.

Top sample is copper and lower brass.
Test solution is just copper sulphate about 5%. The brass reacted within 20 seconds to discolour and darken quite a bit. The copper remained unchanged in that time. Leaving it longer caused some darkening of the copper also.
I realise this is far from fool proof as even copper comes in alloys which would probably react to an extent. But in my case this will be sufficient for today.

[Robert Clarke]

Any other suggestions are welcomed BTW!

[Dennis P Brown]

Conductivity - Brass is about 1/4 as conductive as pure copper. So, an ohm test across a given length, say a cm, would measure very differently between these two metals. Get a known piece of copper and use that as your standard to set the ohm value. Then brass is easy to detect.

[Rich Gorski]

Your photo shows the color difference nicely. I wonder if you can write an APP for a smart phone that can pick up the color difference on cleaned samples. By cleaned I mean something as simple as sandpapering the surface. Maybe you can enhance the color difference by use of a proper optical color filter. You can also have samples of copper and brass/bronze with you for comparison.

Rich G.

Ps. This sounds like a job for a smart phone APP with AI

[Daniel Harrer]

There are apps for colour-blind people that show you the RGB of what the camera currently points at. Maybe even a common name for the colour, but haven't seen that. So no need to code your own thing, those should do.

Sulphur chemistry sounds indeed a good approach. If you want then I can compare the effects of the various ions (sulphate, sulphide, thiosulphate) on both metals.

Lastly there is quite a bit of stuff between brass and pure copper on the Galvanic series, including tin. Tin chloride might thus work but I've yet to try.

[Robert Clarke]

Folks thank you all for these suggestions.
I will do some tests with these ideas later today or tomorrow and come back with results!

Its a curious thing when trying to photograph specular surfaces, or so I have found. One issue that arises is white balance particularly and illumination generally. Controllable on the bench but invariably things tend no to be so straight forward. A textured, matt surface being preferable but not always possible to achieve.

RGB values vary hugely depending on ambient illumination so I would be hesitant to rely on this without a known colour temperature light source and a camera locked to this for white balance. Not impossible but not something I have done yet.

Maybe a little Wheatstone bridge, with 1cm of copper with point contacts as a reference? And 1cm separated probes?

More to follow..

[Dennis P Brown]

Great idea on the Wheatstone bridge approch!

[Rich Gorski]

Found this online...however I'm not sure about the reaction of naOH with copper which might confuse the results.
Rich G.

The confirmation test for the presence of zinc involves performing a color reaction with a reagent like sodium hydroxide (NaOH) to produce a precipitate, which can then be dissolved using excess reagent.


Step 1: Take the sample that you suspect contains zinc ions.
Step 2: Add a few drops of sodium hydroxide (NaOH) solution to the sample. If zinc is present, a white precipitate of zinc hydroxide (Zn(OH)₂) will form.
Step 3: To confirm the presence of zinc, add more sodium hydroxide solution to the precipitate. If the precipitate dissolves in the excess NaOH, it confirms the presence of zinc, as zinc hydroxide forms a soluble complex ion with excess sodium hydroxide, called tetrahydroxozincate(II) ion, Zn(OH)₄²⁻.

The confirmation test for the presence of zinc is carried out by adding sodium hydroxide to the sample, observing a white precipitate, and then dissolving the precipitate with excess sodium hydroxide. This process indicates the presence of zinc in the sample.

To know more about precipitate, visit;

brainly.com/question/30386923

[Rich Feldman]

Chemists like to say “if you aren't part of the solution, then you are part of the precipitate”.

I think the electrical resistivity approach, if material isn't in wire form, would be difficult in practice. Four point probes are standard for resistive sheets and bulk material. But for copper to get up to 1 milliohm per square, it needs to be thinned down to "half ounce" (about 2/3 mil or 15 micrometers thick). For four-point probe on bulk material ( thickness >> probe spacing ), V/I would be in the microohm ballpark.

Here's another idea for Robert.
Take a sample of the metal, and heat a corner to red heat with a torch. Then cool it (quenching in water is OK) and clean surface with a mild abrasive scrubber pad. Copper will look the same with or without heating. Brass will look more copper-colored in the area where surface was de-zinced by heat.

[Robert Clarke]

This evenings Tin Chloride results. The bottom two tests are about 20 seconds each. Certainly the Brass darkened faster but there is still a bit of ambiguity. My Tin Chloride was very acidic, could this be an issue?

The conductivity option is very interesting. I see Bronze is on 1/6 the conductivity of copper.

[Robert Clarke]

Thank you all for your input.
To complicate matters, tests must be discreet(ie: small/non destructive) and possible to do in situ, without removing the part.

Micro-Ohm! Ah crap. I was hoping some kind of pogo probes might suffice in combination with the Wheatstone Bridge but I'm guessing at these resistances any variation in surface texture will disrupt the readings. That said. if multiple readings were made an average must appear; and if multiple known samples are used as reference then might the conductivity approach work?

[Ryan Ginter]

I'm not sure if this would count as non-destructive testing, but perhaps you could differentiate them from their hardness? Brass is generally much harder than copper, so using a tool that is only just capable of scratching copper shouldn't scratch brass nearly as easily. Besides that maybe sound could be used. I would try hanging the sheets from a string and ringing them with a quick, hard tap. Of course, the sound method would only work if you were directly comparing materials of equal dimensions.

The only fool-proof method I can think of off the top of my head is X-ray fluorescence, but that would require the possession of an X-ray tube, a 70+ kV power supply, and a gamma spectrometer.