All Metal Mode and Voids in The Ground Question

Hi Folks,
Hope everyone here is doing well, been a while but im back with a question... I metal detect an old school built in 1926. I went to this school starting in 1976 and finished in 1982 in 6th grade. Our 6th grade class buried a time capsule with our class photo and other items. I have started searching for this capsule and my 6th grade teacher has also aided with information. The area we are most certain it is in, is not that big of an area. To the best of our recollection the capsule was plastic with possibly metal clasps for closing, but we arent sure. Well while going over some of this area in all metal, i have come across 2 areas that completely make the detector go silent. After the coil has passed over this area the hum of all metal returns. Have any of you ever experienced this? Could this possibly indicate a void due to something hollow or similar? Thank you for any assistance and as always i find this is the most intelligent and informative of forums one can have the opportunity to be a member of. Have a great afternoons fellow hunters.
Frank

Hi,,,I'm kinda curious what metal detector you are using???? The nulling could be from iron or some other mineral deposits in relationship to your ground balance setting or settings of the machine itself....Especially if you are using a ferrous & nonferrous TR or BFO detector .... If you are not certain that your time capsule contained any metal, then your best option is a probe to locate it.....A simple small diameter rod with a handle should work for this purpose.....Good luck....JJ

Hi JimmyJiver,
Using a modified Teknetics Mark 1. I have had a Mark 1 for years and know the machine like the back of my hand but cant figure this one out. Thanks JimmyJ
Frank

Well,,
My thoughts,,the same here as actually detecting for metal.

When in doubt,,DIG it out !!

Very likely that's why the threshold is cutting out... Guys used the old whites analogs to locate bottle dumps.

Could be that you've located a highly mineralized (magnetite or iron ore) ground area that is causing a negative response (null threshold) in all-metal mode.

A mechanical probe is definitely worth trying. One way to make a shorter one is to use a bicycle spoke. Racing bike (700c) wheels use spokes of 300mm (12 inches) length, 2mm diameter. Cut off the J-bend, fit the threaded end into a plastic handle. For longer lengths, have a look on bottle-digging websites for bottle probe construction guides.
Re: the detector, the nulling could be non-mineralised areas, such as stones, best to dig to find out.

High probability that some form of iron (iron oxide) is causing your audio 'blanking'.

In addition....... you are possibly looking for iron clasps on the container.

I used to use the Voids on the 5900 to look for underground openings..

Bottle pit's..

Rough on stump holes though lol..

Keith

“I don't care that they stole my idea . . I care that they don't have any of their own”
-Nikola Tesla

Yes I have experienced that.
Was testing for the British MOD with a variety of detectors and while using an X-Terra 705 with 10" DD coil I happened to mention I thought that I "detected voids" in the test lanes that seemed to get them excited by my findings!
I've experienced it about two other times in the wild - was using a Sov and an Explorer

It can occur but folks misinterpret the event as it's such a rare occurrence.