A question for discussion please...

Over the years I've noticed this. Everything we hunt for falls into a certain range. Iron to Gold to brass to lead to aluminum to say silver to clad coins and buttons not necessarily in that order in real life. They all follow an incremental scale up the ferrous to conductive range. Some detectors follow what I call a great scale, easy to pic the items out to dig. Other detectors are all over the place ID wise with different metals we hunt for, I'm just wanting to get an idea if this is a metallurgical scale, a size of the object scale, a little of both? Just wondering....... Thanks

Having used many units over the years which is the normal for most forum members its up to the detectorist to get to know where most objects fall on their meters. Most units differ to a degree and guess that's whats called knowing your unit which comes with many hours in the field. Would say the one unit detectorist has an advantage as switching between several units which most of us do can become confusing.
Not into the internal makeup of units but imagine many units differ how they work causing these differences...Knowing what your detector in hand is telling you will surely aid in finding the goodies..

Jack...

You ought to check out this excellent book for sale on Amazon "Taking a Closer Look at Metal Detector Discrimination" by Robeert C. Brockett. It is a very good read on why metal objects respond the way they do, although it is old (1980's) it is not outdated, $13.95 on Amazon, I may have to buy another one as I cannot find mine, it is that good and it has a lot of stories on why you should dig pull tabs.

In a nutshell: Conductivity, Mass, Size.

For example: In the United States....... silver coins are 90% silver and 10% copper. This is called "Coin Silver". A silver Half Dime...... and a Silver Dollar are exactly the same composition. Metallurgically.... they are identical conductivity. Their diameter vs thickness is identical/proportionate. On a F75...... the ID of each identical conductive target ID's as

Half Dime = 62
Silver Dollar = 92

The differences: Size, Mass, Surface Area

There is a much better explanation of this phenomenon in the Gold Coins thread on the 2nd page of this forum. ((( Look at the huge conductive span between a $1 gold coin ... vs ... $20 gold coin.

I'd say:
Conductivity of the raw metal; Size (in all 3 dimensions, but especially the thinnest); state of corrosion; specific shape of the item.

Conductivity of the raw metal/alloy the item is made of has a significant effect, because the conductivity can vary over a >50:1 ratio from best to worse. The best pure elements are silver and copper, and for real-world finds, copper, high copper content bronzes, Sterling silver (92.5%), Coin silver (US=90%). Worst is stainless steel (rubbish), lead & cupro-nickel (poor), through zinc, bronzes, brasses, aluminium alloys etc.
Here's a link to a table of data showing different metals conductivity. The figure to look at is the IACS one, where copper = 100%.
[eddy-current.com]

Size is moderately important, if you consider it in a straightforwards linear dimension way. Eg. a 16mm diameter musket ball would read quite a bit higher than an 8mm one. But if you think about the resulting weight, the big one is 8 times heavier, so weight of the item is not such a significant factor.
If the item is thin in one dimension, eg. a coin, aluminium foil, this can start to have a noticeable effect on the way electric currents flow. Here in Europe, we have old silver coins that are very thin, often around 0.3mm (0.012 inch), and that contributes towards making them read much 'lower down' than you might expect.

Corrosion has a significant effect on certain metal alloys. Many brasses & bronzes corrode heavily, typically the tin or zinc leaves the item, the remaining metal has a very uneven surface and the remaining bulk of it is porous (on the microscopic scale). This makes it conduct electricity much less readily, dropping it down the scale. Even sterling silver (92.5%) can lose its copper over time.

Shape has a small part, but one particular shape that stands out is a ring/loop of metal, eg. finger rings, nuts, washers, ringpulls. These read noticeably 'higher up' than a 'broken' piece of metal of the same size, it's almost like the 'hole' is filled in. This can even help iron read as non-iron. In Europe, we find nuts, washers, other iron rings, that have come from old farm machinery (steam engines etc), they fool detectors quite well.



Edited 1 time(s). Last edit at 11/26/2014 10:19AM by Pimento.

Just 2 cents more... last night I took the half dozen gold rings I have found in the last year and waved them under the nose of my G2. All fell under common US coin readings (4 were 14k, 2 were 10k). They ran from low 40s to low 50s on the G2 and some were not smooth sounding at all. Shape and volume were the main variables as far as I can tell. An open ring (broken or gapped) is much weaker than an intact one signal wise. A large ring is much higher reading than a fine one. Stuff we learn pretty quickly but may be helpful to the newbies or those who have a different hunting experience.

Past(or)Tom
Using a Legend, a Deus 2, an Equinox 800, a Tarsacci MDT 8000, & a few others...
with my beloved, fading Corgi, Sadie