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Brian

Why Do Bottle Caps Sound Scratchy?

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I've been wondering for a while why bottle caps tend to have the scratchy sound. I can't seem to find an answer on google either. Is it because of the rivets in the sides of the cap or ferrous material inside the cap?

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The iron in the metal and the jagged edge. 

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Most modern bottle crown caps (not the screw on caps) are made of zinc or tin coated steel. What the composition of the steel is I don't know as far as alloys. Then there are the ones that have aluminum foil coatings and of course the ones that have corroded and rusted. So, lots of different surfaces exposed to the Nox multi frequencies and who knows how many different metals mixed together and oxidizing that react differently to the Nox. Coronas drive me crazy since they rarely give much of a ferrous response in my mineralized area. 

If you are able to get bottle caps to sound scratchy on your Nox consistently you are lucky and maybe you can use that characteristic sound as a "tell" for caps in your area.

 

Jeff

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Bottle caps are not at all uniform in their alloy structure.  Different companies use different metal mixtures so to speak.  Your detector is trying to analyze the metal object beneath the coil and sees a somewhat complex compound so it reports back what it's seeing.  Also, the shape and state of preservation affects the signal.  A crushed, rusty cap will give off a different signal than a pristine one of the same type.

It's not that the detector is at fault in my view, its a precision machine that's trying its best to analyze the impure metal it sees. 

At least this is what I've discovered on our beaches....other views of the battlefield could very well differ.

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Here’s what I posted on Dankowski a while ago...

I have puzzled over this question for a while - what are these “steel” caps made of. After wasting an hour on the web I have concluded that it is likely that they are “Tin Free Steel” or TFS. This differs from “tin Plate Steel” or TPS by the use of metallic chromium instead of tin in the laminate. TPS is what most cans were made of - TFS is used because of its superior anti corrosion qualities and its suitability for painting or other decorative exterior finishes. 

Tin Free Steel 

Features 

TFS has excellent lacquer adhesion properties allowing use for food cans, beverage cans and general line cans. 
Excellent resistance to black sulfide stain makes it the most suitable material for making fish cans. 
Even when the same surface finish as TIN PLATE is applied to the substrate steel sheet, 
it provides the unique surface luster characteristic of metallic chromium. 
 

2C31FAAE-58FB-4FF8-85C6-C879FE1AB99C.jpeg

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Rick illustrated the facts much better than my view from 50,000 ft.

Good job Rick  👍

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