Metal Densities And Conductivity

[kac]

I always wondered why some targets have a tone roll and others are flat. I thought it might have a lot to do with target density and their conductivity so I plotted it out. This doesn't include size, shape, orientation or depth, just a raw comparison of metal types. You will notice when the 2 values are close the drop of on a target is quicker. What is really interesting is Aluminum is slightly overlapped. Also notice how extreme gold is. Keep in mind conductivity will translate to phase angle. Chart isn't in any particular order of metal type. Something to think about.

[IBMe]

Man did you strike a nerve. Valuable information ignored by metal detectors. The density is in the audio. Most, by the time it gets through manipulation, it may be hard to discern.  I had an F5 a while back, you could clearly hear the density.

As your graph shows, they are two different scales.

Why don’t we have a density number along with a conductivity number? It’s there, you can hear it.

Another thing ignored is target width, except Garrett GTI 2500.

Why ignore information?

[IBMe]

For a while, back when I had an F5, I used to carry and nickel and a tab in my pocket to recalibrate my brain on density. It’s hard to hold in head.

Put a little graph on the screen that gets lighter and darker based on density. Maybe an alarm that goes off at a certain density.

Give me the target width when I use pin pointer.

Mostly ignored wealth of information.

[GB_Amateur]

I'm curious as to where you got these conductivity values and what the units are.  Maybe just a typo, but tin is not close to the second most conductive element in your list.  Lead also is out of place.  (This is my reference.)

Another point worth noting is that all except brass in your list are pure (100%) single elements.  With the exception of Large Cents and Half Cents (which are pure copper), among US coins made for circulation all others (AFAIK) are alloys.  Alloys can have considerably different conductivities than any of their component elements.  Gold jewelry is an excellent example of this.

Having said that, you may still be onto something.

[RONS DETECTORS MINELAB]

Some good links here also!

https://metaldetectingforum.com/index.php?threads/conductivity-and-metal-detecting-explained.283119/#:~:text=A higher frequency in a,meals such as silver coins.

[PimentoUK]

The flaw in the data is the electrical conductivity values.
These are PURE element data: you need to use realistic accurate alloy data, then you may have something to analyse.
For example: 24ct gold is almost never encountered, and the electrical conductivity is VERY influenced by alloying. Even 'coin alloy' 0.900 fine gold has a miserable conductivity, almost the same as pure tin, and only half Edit: twice the conductivity of lead, for example.

[ I used tin as my metal of choice to make 'fake' gold dollars, many years ago on Tom Dankowski's forum - these were physically very close to the real thing in diameter/thickness, but using pure ( or close ) tin solder. As a result, they ID'ed the same as the gold original, and ideally would give the same signal strength, and other behaviour as them, too  ]

And 'drinks can' aluminium is quite a fancy alloy ( hence the very high strength ), and this results in conductivity dropping significantly ( from memory 67% IACS down to 37% )
Even lead isn't guaranteed pure, all kinds of contaminants can be included, tin being an obvious one, but bismuth and antimony can be there. ( we often find printers 'type' blocks in UK farmland. They are made from a lead alloy called 'type metal' , and when the printing industry is finished with them, they get repurposed as 'lead', for casting musket balls, and anything else that lead would've be made into )

[Geotech]

I agree with the comments on conductivity; First, your values appear to be wrong and, second, alloys are all over the place. Here is a plot of cupro-nickel alloy conductivity:

It doesn't take much nickel to drag conductivity way down.

I strongly suspect that the tonal quality has more to do with shape and iron content rather than metal density. Here's an experiment: obtain a bunch of targets that are all round discs but of different metals: gold, silver, copper, nickel, aluminum, brass, lead, zinc, & tin. Most of these can be found in coinage but lead & tin may have to be fabricated. Preferably all similar sizes. Here are some rectangular targets I have that are all 1-ounce rectangles; these would do just fine.

Test them for tonal quality. I expect they will all be about the same: clean tones. The exception will be if you have a multi-tone detector and a target is on or close to a tone transition.

A round non-ferrous disc is a very well-behaved single-domain target, at least when buried flat. At angles or on-edge it is still usually well-behaved, but may detect off-center or with a double response. Jewelry, pull tabs, can slaw, and the like are multi-domain targets and the dominant VDI can change as the coil sweeps over the target, resulting in tone roll.

Ferrous targets can be ill-behaved in multiple ways, depending on whether they have a substantial eddy response. Ferinstance, a bottle cap can exhibit both ferrous & non-ferrous responses as the coil sweeps over:

At points a & c the response is ferrous but at b it's a non-ferrous eddy response. A decent detector with fast recovery should report at least a bad tone roll; and maybe even a distinct bonk-beep-bonk. Old, slower detectors will report the peak response, which is at b.

 

[GB_Amateur]

6 hours ago, PimentoUK said:

Even 'coin alloy' 0.900 fine gold has a miserable conductivity, almost the same as pure tin, and only half the conductivity of lead, for example.

Although I agree with most of your post, I think you have the lead vs. tin conductivity info reversed.  From Kaye and Laby (see link in my post) the resistivity of tin at 0 degrees Celsius (freezing point of water) is 11.5 x 10^-8 ohm-meters while the corresponding resistivity of lead under similar conditions is 19.2 x 10^-8 ohm-meters.  Since conductivity is the reciprocal of the resisitivity (i.e. 1/resisitivity), the conductivity of tin is higher than lead, not lower.  To be more precise, at 0 C the conductivity of lead is close to half the conductivity of tin (11.5/19.2 = 0.600), not the other way around.

Here's a plot I posted here years ago, similar to Carl's plot but of gold alloyed with either copper or silver instead of copper-nickel alloys as he showed:

Note that the conductivity of 90% gold, 10% copper (as used in USA gold coins 1837-1933) is near the lowest conductivity of any gold-copper alloy -- illustrating a point PimentoUK was making in his post.

[kac]

Conductivity was for the base metals not alloys. Formula on conductivity was off several sites and all had a value*log7 or log6

As I mentioned this doesn't take in account size, shape, orientation or depth.

What I do think is if a machine has a consistent swing speed it might be able to also be able to identify material by signal drop. The roll many have learned on the older machines. Many modern machines seem to lose those rolls especially as we muck around with recovery speed.