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Question about Gold

A

Anonymous

Guest
I just dont understand why gold show up like pull tabs, it is a very conductive non ferrous metal, you would think that it would show up close to Silver. I just dont get it?
HH
Ray
 
I believe it is because gold is a soft metal. Which will allow the frequencies the detector sends to be absorbed and less reflected back to the detctor. Where as silver is a hard metal and absorbs less of the frequencies and reflects more of the frequency.
 
the electroconductivity for Silver is 0.630 while Gold is 0.452
So that's a start at "why". As for Gold containg ANY iron as posted below, what of gold coins and bullion that are .999 Fine, which is essentially pure?
As it relates to metal detectors, remember that the signals are interpreted with coin sized objects in mind. This is why an aluminun can which is lower conductivity than silver shows up as silver, it is MUCH bigger than expected, give a larger return signal than expected, and thus gives (false) conductivity measurements that are much higher.
The ferrous component reading is partially derived from the "decay" of the signal. A piece of iron is magnetizable, and thus "stretches" the signal as the magnetic field colapses. Items with ZERO iron content can register as "ferrous" if there is something about the shape or configuration that "stretches" the signal in the same way a true ferrous object would.
So, every detector suffers from being "faked out" by odd shapes, target sizes beyond the scope of what a typical metal detector is used for, and so on. When you consider we are "looking" through solid soil chock-full of minerals, fertilizers, salts, and so on, the ability to ID is quite remarkably advanced.
Wait until we have NMR (Nuclear Magnetic Resonance) detectors in the future. Not only will we be able to ID coins, but to display the exact metalurgical composition before we dig it! How cool would it be to have a machine that told you is was a War Nickel before you even bothered to dig?
DAS
 
Very good explanation as usual. It is interesting when you read the ideas we have about how this detector or others work for that matter.
I read some material on a commercial detector in Germany that can detect and ID metals inside of foil. I was not that interested in the detector but that is was based on the fact that foil is not magnetic. With ferrites and iron in the magnetic class if we can get past iron minerals and refined iron it will be a great leap forward.
HH, Cody
 
My opinion is this. We need to take in account that most rings are not 24K gold. Most rings range from 18k to 10K. The amount of gold will give a stronger signal, and better response. Men's rings, will hit toward the top middle on the Explorer II, and some Lady's rings as well. Most of your lady's rings will hit the bottom center because they, have less gold weight or less gold content. 10K rings do this because the gold is mixed with more nickle and silver alloys. So will 14K rings. Check this out, you will find this to be true. Gold coins will hit bottom to upper middle on the screen slightly higher than a ring. I know why I don't dig allot of gold coins, it's because I ignore allot of nickle and aluminum signals. Unless I'm on the beach of course. The ratio on the beach to find gold is about 1-100 pull tabs. So I dig them all there. I hope this helps.
Tom
 
Also pure gold is one of the highest conductors available. Right up there with Silver and Copper. But gold is rarely used in it's pure form because it is too soft. Gold is normally alloyed with other metals to make it stronger which is why most Jewelry is 10K(41%), 14K(58%), or 18K(75%) gold. Once gold is alloyed with another metal it's conductivity drops dramatically. Pure Gold's conductivity rating is around .8 with 1 being a perfect conductor. But once gold is alloyed this figure drops down to around .2 Which is down close to that of a nickel whose conductivity is .15 This is the reason that most gold rings read in the nickel-pulltab TID area on most detectors. Hope this helps.
HH
Beachcomber
 
directly from an electronic (PDA) "Periodic Table of the Elements" program, so I'm curious as to the origin of the conductivity = 0.8 statement you made.
The reason I ask is not to challenge you or to claim my data is better than yours, but to find out if my PET program has been lying to me. I use the thing all the time, and I know for certain the author would appreciate an update!
I also use the linked site when I've left my PDA elsewhere.
Thanks for any feedback.
DAS
 
Well gold is popular because it does not decay or get tarnished like other metals. Dig up a gold coin and it may look just like the day it went into the soil. The metal of the gods. It does this because it doesn't react with the other minerals and acids in the soil. This also means fewer particles of gold enter into the soil to produce a halo effect.
So gold coins retain more of their original signature. This may be why the size of the gold coin influences so much where it appears on the screen. There is no halo.
Take silver and copper that erode in the soil much faster. The halo they create or footprint must be very large indeed. Compared to a gold halo they must be enormous. And also I expect a copper halo for a half cent is not much different from a large cent. The washing of large amonuts of small bits of copper into the surrounding dirt likely causes this.
My guess is it is the halo formed by coins that prevents copper and silver coin size from effecting the reading so much as it does with gold. Platimnum might behave much the same as gold.
If copper and silver did not halo then coin size might be more of a factor.
If anyone starts finding platinum coins please call me and I will give you half of everything I find.
Thanks. <img src="/metal/html/glasses.gif" border=0 width=15 height=15 alt=":geek:">
 
so the size of the coin has more influence on th eoverall strength of the signal i.e., conductivity.
 
Conductivity does not change depending on surface area or size. A silver plate has no more conductivity than a silver dime. What changes is the conductance or amount eddy currents that flow in a give period of time. It was mentioned in a post above about the decay of these currents which is getting to how targets are identified. Iron minerals will skew the reading to the left of the screen or towards more ferrous and less conductive based on the two axis of the display Minelab uses. That is one good reason for a more open screen or IM setting towards IM-16 so when the targets skew they give a two way hit instead of one way. The target size has more surface area for the lines of force from the coil to strike and induce eddy currents. Although iron has less conductivity than silver if the surface area is large then iron will also give a better signal even if the iron is in a high state of decay which does not support eddy currents flow as good as newer iron. So, I think it it is the larger surface areas for the induction of current that is a primary variable for depth while conductivity is a primry variable for target identification.
HH, Cody
 
I probably have the decimal in the wrong place. It probably should have read 83 rather than just .8 I had rounded it off as I couldn't remember the exact number. I ahve been looking for the website that had the info but have not been able to find it. It took me two weeks of searching to find the info on gold alloy conductivity. I thought I had bookmarked it in two places so it wouldn't get lost but I am still looking. If/when I find it I will post the link. Apparently it is very guarded infomation <img src="/metal/html/smile.gif" border=0 width=15 height=15 alt=":)"> <img src="/metal/html/smile.gif" border=0 width=15 height=15 alt=":)"> <img src="/metal/html/smile.gif" border=0 width=15 height=15 alt=":)"> It's very easy to find the condutivity of pure metals but the conductivity of alloys is hard to find.
HH
Beachcomber
 
You are correct to my knowledge. Gold is one of the best conductors and does not tarnish as bad as othe metals. It is the alloy of gold with other metals that accounts for the decrease in conductivity but it still is a very good conductor. Iron ferrites in the soil are what causes gold, silver, or copper to skew to the left of the screen and at times lower on the screen in conjunction with the allow of gold to harden it that gives rise to the idea it is not a good conductor. Metals do not absorbe the frequency from the detector based on how soft gold is. What is measured is the disturbance in the inductively balanced electromagnetic field between the TX and RX coils in the search head. It is really not a reflected field such as a radar beam stricking an object and bouncing back. These type of signals can be absorbed like an aircraft that is hard to detect due to the type and shape of material on the surface fo the craft. The electromagnetic fields are 90 degree out of phase for detectors so never leave the coil but only expand outward and then shrink something like working an accordian.
HH, Cody
 
Hi Ray
Can I assume when you mention gold, your referring to gold jewelry, and not pure gold ? Gold jewelry because it is alloyed, will come in at a low conductive level. That why it
 
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