Cache Test

[Carl-NC]

OK, here is the "official" run-down of the cache test. This is a repeat of the test described on Gary's Detecting site, in which Gary claims a decent sized cache cannot be detected at a mere 2-feet deep. Now, lots of folks were skeptical about that test, but all good science is subject to independent verification

Since I was curious, and didn't see anyone else digging a big honkin' hole, I thought I'd try to prove Gary wrong. I s'poze have two advantages in performing this test. One, I gots lots of silver on hand to make up a cache. Two, I gots lots of detectors to test. About 100, though I'm now thinning the herd.

I decided to roughly match Gary's setup... he buried 1kg (2.2 pounds) of coins, copper & silver mixed, about 25-inches deep. I chose 3-pounds (220-count) of silver US quarters. This gives me an edge... a bigger cache, and all-silver so it has higher conductivity. However, I intended to go a little deeper, but my digging was abruptly halted at 30 inches by sandrock, and I was fresh out of dynamite. So the top of the cache container (a plastic Betty Crocker frosting tub, circa 1990) ended up exactly 24 inches deep, and the coins came up an inch below the lid, for a perfect 25-inch match to Gary's setup.

The next posts show some photos.

- Carl

[Carl-NC]

Here is the cache... 3 pound of 90% silver coins.

[Carl-NC]

Here's the hole, with Betty Crocker ready to, errr... go down.

[Carl-NC]

Bucket o' coins at the bottom of the hole. Like Gary, I also notched out a little side cubby to stick the coins in, so the soil immediately above the cache is undisturbed.

[Carl-NC]

Depth as measured from the top of the container. Exactly 24".

[Carl-NC]

Hole is covered. I'm seriously concerned that when the grass recovers, I may never be able to find my coins again. I need to add some method of marking the spot.

[pml]

That's some great testing there.

I decided to roughly match Gary's setup... he buried 1kg (2.2 pounds) of coins, copper & silver mixed, about 25-inches deep. I chose 3-pounds (220-count) of silver US quarters. This gives me an edge... a bigger cache, and all-silver so it has higher conductivity.

I would have to disagree with that. I believe that a PI can take advantage of the fact that lower conducting materials has a faster di/dt decay time, which means higher voltage. Remember that the increase in the coin/nugget's eddy current will be about the same regardless the metal type, to within reason, because the pulse should be fast, meaning it's mostly inductive, not resistive. But when the applied voltage is removed then the coin/nugget will decay at a rate depending on the resistance of the metal.

Well, that's just PI and nothing to do with VLF's, and that's assuming the PI is tuned for the lower conducting metals such as natural gold, not coins.

Paul

[Carl-NC]

True, but I believe all of Gary's tests were with discriminating VLFs... in fact, he specifically said he would not test a non-disc detector, because such a beast would be unusable in England's iron-laden fields.

But I still think PI's should be tested, to see if any will pass the test. They would be useful in many other cache-hunting scenarios. A better PI test would be to bury 3 pounds of gold coins... alas, I'm a tad shy of that mark.

- Carl

[pml]

You know, while having new tires put on the car yesterday I was scrounging around for lead tire weights. I found one, but it sure don't look like lead. I'm wondering if they're using some cheap substitute now days.

I don't know how lead compares to gold, but you're right gold is expensive. You could try tossing a jar full of tire weights, without the steel hooks.

Just a thought.

Paul

[Joe(TX)]

GARY's CACHE TEST

The problem with Gary's test is that no time has been given for the halo effect. Silver Coins buried for 100's or 1000's of years should have a tremendous hallow effect especialy if the container was iron or brass,etc. But even if the silver coins are buried in a ceramic type of container the silver would leach and hallow out! This test must be an ongoing one to test every 6 months or so. But after 6 months to a year I bet that I could locate that cache with my Garrett BFO discriminator with the 12 by 24 inch or 24 inch magnified coil or with a pulse Induction detector with a very large coil. Another note is that the plastic tub may not let the coins hallow out at all.. ANCIENT CONATAINERS WERE NOT WATERPROOF....Maybe you need to poke a few holes in that tub!!??? Just my knowledge of 35 plus years poking around for treasures!

[Carl-NC]

Joe, a number of people have looked into the "halo" theory, and I think it's close to being busted. Gold absolutely does not create a halo, and silver and copper probably do not, either. Yes, they corrode, and they probably leech some atoms into the surrounding soil, but this does not increase the eddy current response. Iron is another story, and it does produce a halo effect.

I have an experiment on halo effect planned for this summer, starting next week, actually. Should be interesting.

And, I also have a Garrett BFO with both the 12x24 and the 24x24 coils... I'll give it a try.

- Carl

[pml]

That's pretty cool. I've never even doubted or thought twice about the halo effect, but what Carl is saying makes sense. As Carl said, Iron produces halo effect. That makes sense because iron is a magnetic material. If you have a 1" square piece of magnetic material, and say at 3 feet away it produces a returned signal of 8 units. Now if you break that square into 3 x 3 x 3 (27 chunks) and appreciably separate the pieces you should get a returned signal close to 8. That's how proportionally square magnetic materials work; i.e., not much change in *effective* permeability. Ferrite rods is an entirely different story because a change in length versus radius changes the effective permeability.

Eddy currents in electrical materials greatly depends on material size. So if you break a square chunk of copper into 27 pieces then you decrease the eddy currents by magnitudes. So I can't see spread out atoms of gold or copper producing any noticeable halo effect, but I guess anything's possible.

Paul

[Qiaozhi]

Halo Effect

Joe, a number of people have looked into the "halo" theory, and I think it's close to being busted. Gold absolutely does not create a halo, and silver and copper probably do not, either. Yes, they corrode, and they probably leech some atoms into the surrounding soil, but this does not increase the eddy current response. Iron is another story, and it does produce a halo effect.

I have an experiment on halo effect planned for this summer, starting next week, actually. Should be interesting.
- Carl

That would be a very interesting experiment indeed.

Many years ago, using a simple IB machine, I detected a George III copper coin from 1797. These coins were known as Matthew Boulton's "Cartwheels", and were some of the first copper coins produced in the new fangled steam press. Its diameter is 35cm and is 3mm thick. This coin was detected at a depth of 11", which was pushing it somewhat for this particular machine. In fact, I almost gave up digging, and then "voila" - there it was at the bottom of the hole! Once removed from the hole, the same detector could only manage to detect this coin at a distance of 9". This is contrary to expectation, as all detectors can achieve better detection distances in air than in the field. Also, this is not the only example I have enountered over the years. So - is this caused by the halo effect?

Carl - hopefully you won't need to wait 200 years for the halo to occur.

[pml]

I'm wondering what would happen if you have some salty wet ground mixed with metallic atoms. I guess given enough time anything's possible.

That's enough of my 2 minute analysis, lol.

Paul

[Joe(TX)]

Gary's Cache Test

Carl, How about doing a variation of the test but this time bury the coins in an iron pot, Coffee can, etc but keep the size about the same size of the plastic tub that you used. Also do the same but use a Glass mason jar with a zinc lid. Keep all the parameters the same as Gary's test. I plan to do the same....Also I plan to keep the site watered and will report on the results. May take a week or so to get started as I'm leaving on vacation today for a week.