The simple answer is you can back off the settings on most any detector and notch out the bottle caps. On the CS you might be able to in some cases. Reduce the Sensitivity and Threshold to test. The majority of the time nothing will keep a crown type bottle cap from reading as a "coin" signal. The CS likes round things including harness rings. And as Chuck VT says bottle caps aren't iron or even pure steel so they will not behave as a piece of cast iron or cut nail as far as reject goes. They are basically low carbon mild steel sheet with coatings. And there is a lot of variation. I also find a big difference depending on if they are flattened.
You can see in this text that there are 2 types of crown caps: tinplate and tin free steel (TFS).
I personally want more finds than less so I want to dig all the bottle caps. Tin can lids are no different. They could be an Eagle breastplate.
Here's some details gleaned from the web about bottle caps (crown caps). :
The crown cap that was registered in patent office in 1892 was invented by William Painter in Baltimore, USA. The cap was originally made of tinplate and sealed with 1/8 inch cork inset adheared to tinplate by egg white albumen. Since the middle of the 19th century about 150 different technical designs of bottle closures have been developed in the USA. None of them though have been able to fully replace the crown cork, that still has a market share of 70 % in the EC.
Our crown caps are made of tinplate, electrolytically lined with tin, or of chromium plated sheet metal according to DIN 6099.
Electrolytic Tin Plate is a Tin Mill Black Plate product which has been coated with tin by electrolytic deposition. It is furnished in a variety of tin coating.
Electrolytic Chromium Coated Steel or Tin Free Steel is a Tin Mill Black Plate product which has been coated with metallic chrome oxide by electrolytic deposition. ECCS / TFS is only available with one standard coating which is equal on both sides.
Tinplate – cold-rolled sheet of low-carbon steel coated with tin or a special chromium alloy to combat corrosion. Tinplate is used for example to make food and drink cans, crown caps and jar lids.
Tin Free Steel (TFS) is electrolytic chromium plated steel consisting of thin layers of metallic chromium and chromium oxcide deposited on the base steel which give a beautiful, lustrous metallic finish on both sides. Tin Free Steel offers outstanding corrosion resistance, workability, lacquerability, lacquer adhesion as well as printability. Tin Free Steel has been developed by TCIL as an economical and high quality replacement for Tinplate, especially for the screw and crown cap market. Having high scratch resistance, lacquer adhesion, Tin Free steel is ideal for use in crown caps for soft drinks, fruit juice and other beverage bottles and caps for tomato ketchup, jam and other products.
Tinplate is a low carbon steel sheet (base metal), coated on both sides with a thin layer of tin, throughout on electrolitic process. Since the tin firmly adheres to the base metal, the product may be press molded, stamped, drawn or bent and shaped into complex forms without the tin coating peeling off.
Electrolytic Tinplate -- JIS G3303 / ASTM A624, A626
Tin Free Steel -- JIS G3315 / ASTM A657
.... tin mill black plates or TMBPs, which are further processed in the Electrolytic Tinning Line (ETL) to produce tinplates -- a cold-reduced, annealed, temper rolled and side trimmed low carbon mild steel sheet coated on both surface with tin through the electrolytic process. Tinplates are used by various canning industries to produce industrial cans.
So there you have it ... there's a whole lot more in a crown cap or tin can lid that just iron and that explains why we pick them up with greater sensitivity. Also as some folks have stated round metal objects often read as "coin" on many detectors. I know on my old QII that is true of round iron rings and washers. So far the washers I have tested on the CS do not false badly.
The Fisher Coinstrike Homepage !