Garys Detecting.co.uk
The buried hoard test : I wanted to know how deep a discriminating metal detector could detect a small hoard, so was told to go and get some machines, a big spade and some coins.
These days we hear so many stories about new models going deeper than ever before, we read about people finding coins and artefacts over 2 feet in depth.
Georgi ( The Bulgarian) has always insisted that finding a small hoard at 2 feet is a myth and indeed scientifically impossible using the metal detectors we are all searching with today, I have been told coins with a patina are electronically isolated from one another so in the ground a detector will not see the coils as a mass, more like several individual targets.
Georgi the Nexus designer has always based his resultson facts when testing machines this is why he dropped by to show me what a metal detector was really capable of and busting this myth once and for all.
Note :
 We can only test machines available at the time
 We are not interested in testing a machine with no discrimination circuit as you would not search in all metal on a junky ancient site.
Also this test is to simulate coins buried in a non metallic container which has almost certainly been destroyed, eg: leather pouch, clay pot, wicker basket wooden box.

We decided to carry out 2 tests in my garden (while woman was at work)
Test A to bury a sixpence at 10 inches deep
Test B to bury a small hoard of coins 1kg at 25" just over 2ft...64 cms to be exact
Both undeneath undisturbed soil or as close as we could simulate.

The Test
We dug the hole to 70 cms then burrowed 2 chanels into the opposite side walls 8-10" long
 One at 64 cms deep marked "B" the other at 10" deep marked "A" .
This was to ensure the targets were placed underneath mostly undisturbed soil.



The test diagram
Our earlier tests had proved that the Halo effect of buried coins etc played no real part in detection depth in fact the halo effect only applies to Iron. To prove this fact next time you dig an ancient coin try to detect the soil in which it came out, if the halo effect was true the soil would give off a signal to.
The silver sixpence was placed in pod "A" the 1kg coin hoard was in pod "B" (see diagram).

Machines used
Minelabs,Exp,Sov Big coil,Quattro
Gold Maxx Mk1
Whites, XLT,MXT
Nexus, std coil, prototype coil
Tejon with big coil

Digging starts

The test hole
 It is surprising how hard it is to dig this deep... hell 2 pay when she sees it.

I cant get my head around the Centimitres business

Measurements in inches and centimetres



Before we carried out the full test we buried a highly conductive aliminium piece at the bottom of the hole and the filled it in with the earth 3 machines picked this target up with a faint signal the Minelabs, Tejon (Big coil),Nexus with std 9" coils.
Then we dug the hole out and placed the aluminium piece in the side pod "B" and filled the hole, now we could test it under undisturbed soil.


The pocket is next to the screwdriver

Test Result:
No machine could detect the target beneath the undisturbed soil.
Conclusion
 Loose earth in a freshly dug hole is not a fair test for a machines depth, all machines tested would indeed pick the hole up as part of the target giving a false depth impression.
Eventually we managed to get a digable signal from the Nexus fitted with the prototype ulta low frequency 12" coils.

The highly conductive Aluminium test piece

Placing the test piece in the side pocket for the second test

At 25" deep only the Nexus with the 12" coils was the only machine that produced a smooth signal.

1KG of mixed copper and silver coins some with the original soil still stuck to them

The coins were placed in pocket "B" and the hole was filled in.

Ready for the test

Test results
NO MACHINE COULD PICK UP THE BURIED HOARD IN DISCRIMINATION OR ALL METAL
 NOT EVEN THE MIGHTY NEXUS
The test is now in place for ever, it will be interesting to test new machines in the future.
Next time someone says they dug a hammered coin at nearly 2 feet simply give them a tape measure and a link to this page.
Targets can be possibly be detected this deep providing they are
A: Bigger in mass than our test coins
B: Higher in conductivity than the targets used.
Pulse machines and pipe locators have no discrimination(so not a fair test) I will post results if and when I get one
This myth is Busted
I asked Georgi Can machines that that don't air test well go deeper in the soil.
He said No absolute Crap !! this is scientifically impossible if a machine air tests badly it will detect badly in the soil despite what you read on metal detecting forums and some manufacturers literature.
However some machines that air test better can loose a higher percentage of depth in the soil around 30% depending on what type of search coil is used.
If you suspect these results are wrong, please go out there and do the buried coins test for yourself, I think you will be amazed!!!!.

As for the sixpence at 10" test we will be posting the results soon, but be warned there not good.

Letter from reader