Gold: Low or High Conductivity?

[dustoff]

I've seen several references in print and many comments on forums similar to this: "an aluminum pull tab has about the same low conductivity as gold". Am I not understanding something? Gold wire and gold plated circuit board traces are used in high quality electronic equipment because of gold's very high electrical conductivity/low resistance. Aluminum wire was used in house wiring in the mid-70's due to the very high price of copper then. It's relative (to copper) high resistance caused many problems in breaker panels and not a few fires resulted. So... do metal detectors respond to conductivity in a different way than I learned in school?

I posted here 'cause I'm a water hunter and I primarily read this forum. If it should be somewhere else, let me know. And thanks in advance for any information that clears this up for me!

 

[therover]

Gold jewelry for the most part is alloyed with other metals. Consequently, the conductivity and ID of that jewelry is all over the map. I would think 24K gold jewelry would be a high conductor, and I have read that 24K rings ID as silver on most ID machines due to the high conductivity. 10K ring can ID in a big range depending on the other metals that it's alloyed with. I would think if alloyed with silver, it would be higher in conductivity than if alloyed with aluminum or a metal lower in conductivity than the mentioned silver. I would also think the percentage of the alloyed metal also plays a part in the conductivity range and ID range as well as how many different alloyed metals were used to make the piece of jewelry.

Remember for the most part, when us beach and water hunters speak of gold, we are talking jewelry. Now, the gold prospecting world is a totally different ball game and one I have NO experience in, so I cannot comment on it.

JC

 

[dustoff]

Good point on the jewelery vs gold nuggets. I had assumed the prospecting PI's responded the same as a beach machine. I may post this question on one of the prospecting forums.

Thanks!

 

[TheMarshall]

I've seen several references in print and many comments on forums similar to this: "an aluminum pull tab has about the same low conductivity as gold". Am I not understanding something? Gold wire and gold plated circuit board traces are used in high quality electronic equipment because of gold's very high electrical conductivity/low resistance. Aluminum wire was used in house wiring in the mid-70's due to the very high price of copper then. It's relative (to copper) high resistance caused many problems in breaker panels and not a few fires resulted. [size=x-large]So... do metal detectors respond to conductivity in a different way than I learned in school?[size]

I posted here 'cause I'm a water hunter and I primarily read this forum. If it should be somewhere else, let me know. And thanks in advance for any information that clears this up for me!

***********************************************

Hi there!

First point.....We don't know exactly to what level your school electrical theory was taught, but your question suggests that it may have been limited to DC (Direct Current) i.e. Volts = Amps x Resistance.

To understand how a detector functions, you need to have learned AC theory AND specifically. the Skin effect.
( I doubt if you were taught the latter at school)

Additionally, your understanding of the practical reason for using gold in electronics is incorrect.

It is primarily used for its ANTI-CORROSION properties, and not necessarily to do with it's conductivity.

Talking about high/low conductivity is relative terminology, and ambiguous.

It is far more more illuminating to quote the specific value of conductivity for the type of metal involved. In metal detecting it is imperative that you do so.

Copper is simply the class name of the metal. Copper's specific conductivity depends on its method of refinement.

The same applies to gold, aluminium, etc.and their alloys.



The above comments are just a few starting points....Hope they help you on the learning curve.....TheMarshall.

 

[dustoff]

Now I have somewhere to start!. My experience with skin effect has been primarily in VHF and UHF radio antennas fed with "hardline" where, at those frequencies, one can imagine the signal traveling on the surface of the feed lines, not within the conductor as in DC circuits. Guess I was not figuring on AC resistance at these comparatively low freqs. I have some reading to do. Thanks for all the help...

 

[TheMarshall]

Gold jewelry for the most part is alloyed with other metals. Consequently, the conductivity and ID of that jewelry is all over the map. [size=x-large]I would think 24K gold jewelry would be a high conductor, and I have read that 24K rings ID as silver on most ID machines due to the high conductivity.[/size] 10K ring can ID in a big range depending on the other metals that it's alloyed with. I would think if alloyed with silver, it would be higher in conductivity than if alloyed with aluminum or a metal lower in conductivity than the mentioned silver. I would also think the percentage of the alloyed metal also plays a part in the conductivity range and ID range as well as how many different alloyed metals were used to make the piece of jewelry.

Remember for the most part, when us beach and water hunters speak of gold, we are talking jewelry. Now, the gold prospecting world is a totally different ball game and one I have NO experience in, so I cannot comment on it.

JC

*******************************************************

Hello all.

I have never seen or handled 24 crt Jewelery.

The highest carat is generally 22. Made so to improve its durability.

If you alloy two metals, the resultant conductivity is lower than that of the highest conductivity involved

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This following quote is typical of the ambiguous waffle generated on forums.

"I have read that 24K rings ID as silver on most ID machines due to the high conductivity"

Pure crap.....Sorry, but there's no other polite way of describing it.

TheMarshall

 

[therover]

If you, by your own statement, have never handled 24K jewelry (spelled correctly) then how can you state my statement is pure crap ? I have a 24K ring that ID's as high tone on all my CZ's and VDI's in the high 80's on my DFX so I know what that ring ID's at on these machines...not sure about other ID machines, hence me stating that I have READ this.

Also, please be aware K is for jewelry, C is for 'stones' (ie, diamonds, emeralds, etc). Lets get things straight before you start spewing garbage.

 

[Reg]

Hi Dustoff,

Gold in its pure form probably should be classified as a high conductor since it falls just below copper on the conductivity chart. Gold is a higher conductor than pure aluminum. Now, with that said, most objects made of gold such as rings are not pure gold. A common alloy here in the US is a 14K type gold which is about 56% gold if I am not mistaken. Much of the gold jewelery from Europe has a tendency to be 22K.

24K gold will be quite soft and that is why it is not the most common purity used for jewelery. The alloys simply make it stronger as well as cheaper to own.

Now, as for how gold may register, well, near pure gold will measure higher than a corresponding piece of aluminum but lower than copper. So, it can register quite high on a TID machine. On the other hand, alloy that same gold with silver, copper, or one of the other metals commonly used and that same gold object could register as a very poor conductor, much like lead registers. Here is a chart indicating how dramatic gold conductivity can change just by alloying gold with another metal. As an example from the chart we see that gold can go from a reading of 77 at pure gold to 16 when alloyed with silver such that the gold is only 75%. The 16 reading would place that same gold closer to the conductivity of lead, while the pure reading is much closer to copper.

http://www.deringerney.com/materials/GoldandGoldAlloys.asp

So, there is no set answer to your question. On the older TID detectors the gold range was from foil to silver dollar and that is about as accurate as one can get.

Reg

 

[Eric Foster]

Quite a bit of 24K gold jewelry today comes out of India and China, as an Internet search will reveal. Most gold objects made in the west are a maximum 22K, as stated, for reasons of hardness. Because of migration and ease of travel in recent years 24K items are bound to turn up more frequently.

Eric.

 

[Eric Foster]

Hi Dustoff,

A good conductivity chart can be found here www.eddy-current.com/condres.htm

Look at the IACS column (International Annealed Copper Standard) and you will see annealed copper is 100%. All other metals are relative to this in percentage conductivity. The relative conductivity for pure gold is given, but there are no figures for alloys of it. Just look though at the range of conductivities for aluminium alloys, so you can imagine that gold alloys would also have a wide spectrum of conductivities. Also look at copper at 100% and the figure for pure nickel. Now go right down the column and look for Cupro-nickel and see what has happened to the conductivity. These tables show what detector designers have when trying to accept one type of item and reject another. What type of aluminium alloy is a pull tab?

Eric.

 

[TheMarshall]

Marshall...yes, there is a polite way to describe it
Posted by: therover [ Send a Message ]
Date: 2 hours ago Registered: 4 years ago
Posts: 969
If you, by your own statement, have never handled 24K jewelry (spelled correctly) then how can you state my statement is pure crap ? I have a 24K ring that ID's as high tone on all my CZ's and VDI's in the high 80's on my DFX so I know what that ring ID's at on these machines...not sure about other ID machines, hence me stating that I have READ this.

Also, please be aware K is for jewelry, C is for 'stones' (ie, diamonds, emeralds, etc). Lets get things straight before you start spewing garbage.



Edited 1 time(s). Last edit was 1 hour ago by therover.
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Hi there again Rover, and thanks for your reply.

My post?..

 

[TheMarshall]

Thanks Eric for your timely, informative post on Eastern origins of such jewellery. (English spelling!)

My postal reply to Rover's assertions of 'garbage', was written last night, but left in my 'out-box' and automatically posted this morning at switch on time.

I'm dashing off to the local 'Tip'...(Garbage Disposal Centre, for our US readers)

Getting rid of a lot of surplus electronic test equipment, (Sad day, but times they are a changing.)

Matt.

TheMarshall

 

[therover]

Marshall,

Thanks for the laughs, and yes, I wrote 'spew garbage' in response to 'crap'. All in fun, as it's obvious you are having fun too, which to me in addition to exchanging view points and opinions, is what the forums are all about. Please note nothing was malicious or to be taken to heart in my response. I kinda knew you were referring to what I stated I read and not my actual view point.

As far as the 24K ring goes, it is from Lebanon, where my Mother's family is from. She is actually there now, and she always brings back gold ( and more importantly for me, pistacio nuts !). It is a small/medium sized wedding band and I can get the dimisions if you like. Never tried the single frequencies on the DFX to see what difference in VDI numbers it would be, but if you know the DFX, you can change the VDI normalization feature so not sure exactly where it would fall when that is done. I would think it would still be pretty high.

You are absolutely correct in that not only does the alloy change how the target will be 'seen', but size, weight, etc. are also factors that play into that. I would think a bigger 24K or 22K ring will ID higher than a thinner one.

As far as 'Karat', 'Carat' or 'Carrot !' is concerned...was busting your stones a bit ( no pun intended).

JC

 

[Eric Foster]

Would it not have been better to ebay it?

Eric.

 

[MagnetMan]

Hi Guys,

Silly question: is there ever any characteristics of a particular metal that causes its magnetic signature (ie: eddy currents) to be different than its electrical conductivity? That is, for a given size sample (distance and ground material notwithstanding), is its signal always directly proportional to its conductivity? Also, is there any theoretical way for a PI to distinguish between magnetism (ferrous materials) and eddy currents (from non-conductive materials)?

Thanks!
-Stefan

 

[TheMarshall]

Eric, I suspect that the cost of parcel posting these days would have deterred even the most avid of collectors.

The saddest item to part with was my old (valve) Tektronics storage oscilloscope.

That was from the days of involvement with Photo-multipliers and fast rise-time gamma ray detection circuitry.

I gave the members of my old radio amateur club, first choice, and actually only dumped what was left.

I still have the solid state stuff.

How electronics has progressed in my life time, and I've enjoyed working in many of its disciplines.

Discovered this hobby about 1970, when asked to repair a Compass 'Mineral'(?) detector.

To repair it I first had to trace out the diagram. So my curiosity was aroused.

Built a 'Sandbanks' PI, and I was hooked.

Matt.

 

[Eric Foster]

Hi Matt,

Yes, I had a love for the Tektronix valve scopes. Up till about 8 years ago I had a fully working 565 with several plug in units, plus another 565 for spares and a 564 I think. I dumped mine when I had to move my workshop from Oxford to Devon, but I did retrieve all the valves, which I still have. Valves have come back in fashion in the audio world and a few in the Tektronix can be used for this purpose. What company did you work for? I grew up in Mullards, at their Mitcham and Croydon factories, then moved to MEL at Crawley, where I worked on airborne radar for the TSR2 - remember that? Would have been a super plane, but the government cancelled the project.

Eric.

 

[dustoff]

I wasn't expecting a tiny firestorm as the result of what I thought was an innocent question. I was hoping for a little education, not a somewhat pompous lecture on skin effect. The [size=large]Bold[/size] and Red type really put me in my place!


Thanks for everyone else's help! I think I'll stick to the SEARCH feature from now on...

Dustoff