Tin, Bolts, Washers, And Other Ferrous Items That Read As Non-ferrous

[Steve Herschbach]

When I saw a video showing the Makro Gold Racer recovery speed using two nails and a gold ring, it caused me to reflect on the various internet nail tests. Nearly all employ modern round nails, when these items rarely present issues.

The common VDI (visual discrimination scale) puts ferrous items at the low end of the scale, and items with progressively increasing conductivity higher on the scale. The problem is the size of items also matters. Small gold is low on the scale, and the larger the gold, the higher it reads on the scale. A silver quarter reads higher than a silver dime, etc.

All manner of ferrous trash including medium and smaller nails fall where they should when using discrimination and are easily tuned out. The problem is large iron and steel items, and ferrous but non-magnetic materials like stainless steel. Steel plates, large bolts, broken large square nails, axe heads, hammer heads, broken pry bar and pick tips, etc. all tend to read as high conductive targets. Usually it is just the sheer size pushing it higher up the scale.

Detectors also love things with holes, which makes for a perfect target by enabling and enhancing near perfect eddy currents, making items appear larger than they really are. Steel washers and nuts are a big problem in this regard, often reading as non-ferrous targets.

Oddball shapes cause problems, particularly in flat sheet steel. Old rusted cans often separate into irregular shaped flat pieces, and roofing tin (plated steel) and other sheet steel items are my number one nemesis around old camp sites. Bottle caps present a similar issue in modern areas. These items produce complex "sparky" eddy currents with both ferrous and non-ferrous indications. Many thin flat steel items produce remarkably good gold nugget type signals in old camp areas.

Two general tips. Concentric coils often handle ferrous trash better than DD coils. A DD coil is often the culprit when dealing with bottle caps where a concentric coil often makes them easy to identify. Another thing is to use full tones. Many ferrous items are producing both ferrous and non-ferrous tones. Blocking ferrous tones allows only the non-ferrous tone to be heard, giving a clear "dig me" signal. This was the real bane of single tone machines with a simple disc knob to eliminate ferrous objects. You still heard the non-ferrous portion of the signal. Multi tones allows you to hear the dual ferrous/non-ferrous reports from these troublesome items, helping eliminate most of them.

Certain detectors can also show multiple target responses on screen at once, like the White's models featuring the SignaGraph (XLT, DFX, etc.) and CTX with target trace. These displays show target "smearing" that stands out differently from the clean VDI responses produced by most good items. A machine with a simple VDI numeric readout can only show you one number at a time and the only indication you might get is "dancing" numbers that refuse to lock on. Usually though the predominate response overrides and fakes you out. This is where a good high end visual display capable of putting all VDI response on screen simultaneously can really help out.

the bottom line is there is not a clear line between ferrous and non-ferrous, but an overlap. Many detectors offer a variable control to deal with this - the iron bias setting. Higher settings eliminate more ferrous, but also runs more risk of missing the desired non-ferrous. Conversely, lower settings reduce the risk of missing desired targets, but you dig more trash.

I have been collecting these odd iron and steel items to practice with and to help me evaluate which machines might do best in ferrous trash. The main thing I wanted to note here is contrived internet videos with common round nails often present a misleading picture. Many machines do very well on nails yet fail miserably on flat steel.

Steel Trash Testing

Tech explanation from Laurence Stamatescu at Minelab:

[fredmason]

not to mention the old square nails were apparently a much better grade of iron...I have found many that appeared to be just-made...

Thanks for your unending pursuit of knowledge and for sharing the same.

fred

[Randy Lunn]

Thanks Steve, you have just confirmed several of my suspicions. The amount of rust and the location of the rust on nails and flat iron sheets also seems to add to the signal problems.

[Northeast]

I have no idea why this has popped up as a recent thread but I like it - maybe you thought it was pertinent Steve and brought it to the top of the forum?

The first paragraph at the bottom of the Q & A page describes how high frequency detectors are perhaps not the best at discrimination.  Is this perhaps why the discrimination on my Gold Monster has not been as accurate as I was hoping?  I was expecting miracles of course

Due to the fact that high frequency is not as good at discrimination is that perhaps just one of the reasons that the multi-frequency Equinox is going to be better at discriminating targets - it has the lower frequency range to assist.  Obviously Multi IQ, processing speed, etc is probably having a greater influence but...? 

And the second paragraph at the top of the page where it is talking about positive and negative signals.  So non-ferrous can ONLY give positive signals whereas ferrous are mostly negative but can be positive.   So that made me think that if something is giving a negative signal at all it can simply be dismissed as rubbish - yippee.        But then I imagined a beautiful big chunk of gold that had a heap of ironstone attached and assume that it might give positive and negative signal responses??  

When responding please take into account that I have never used a VLF with TID numbers or visual displays other than the Monster with its simple Ferrous/Non Ferrous read out 

Thanks.

[Steve Herschbach]

I bump old threads now and then if they seem like they got overlooked. Lots of new forum members did not see the old stuff and don’t look back that far.

The part that is missing here is the ground. A detector sees everything under the coil. The ground is a massive ferrous target. Therefore, ALL targets are a mix of ferrous and non-ferrous signals. Almost any non-ferrous target will read ferrous if the ground iron mineral content is high enough.

The assumption is that if a target gives a ferrous signal it might be bad, so skip it. The way it should be done properly is that if a target gives any non-ferrous response at all, then dig it.

The problem as this article notes is lots of ferrous will read as a very high non-ferrous signal. The trick there is the false signal will typically come in around the silver dollar range on a detector with target id. Gold will read lower. Unless your detector does not have target id (like the Gold Monster, just ferrous/non-ferrous) in which case the false signal just reads non-ferrous.

Which is why having actual target id numbers is helpful when dealing with trash.

 

[Domenico]

Further to what has been written in the above answers...

Some searchplaces are so instested with iron that they're pretty unworkabke...Again, I have to bring out european pure nickel coins ( as are canadian coins too) .

You face an iron infested place?  Well, just do as usually, using your best settings for the places.

Then use a NO MOTION mode on the same place, and just ground balance it to salt...

What now will happen is all PURE ferrous targets will be IGNORED, all ferrous alloys will give signals. Pretty useful for relic hunting and Canadian coins hunting.

Purists will state that de detector will not be tuned to the actual site conditions...believers will walk away with finds...

This trick is very useful once you understand it...I had plenty of succes in relics and coins using  this trick with the GBPro in all metal mode, GB to "0"  From then on, you will know what you were missing... 

If the detector beeps, dig !! no matter if the ID is a ferrous one  !! 

Happy hunting...!!