British 20 pence piece with brown patina 1986

Hi, it's me again 🙂
I need to clear up a problem about my 1986 Cupro-nickel 20 pence piece, apparently Cupro-nickel doesn't tarnish, well I beg to differ ! lol
I have one that has a very dark brown patina on it???
Can any one help to explain why mine is tarnished?
Thanks in advance 👍

neither are magnetic.

I had one similar - it had been buried.
Copper-nickel turns dark in soil.

God, I feel like we are always at loggerheads!😂
I have been trying to find out why it is brown and this is what I found before posting here earlier:

Corrosion resistance: Copper-nickel alloy coins do not tarnish.
Electrical conductivity: Copper-nickel coins have specific electronic signatures that help prevent fraud in vending and coin-handling machines.
Antimicrobial properties: Copper-nickel coins are much more sanitary than coins that do not contain copper. This is because copper surfaces kill dangerous bacteria, viruses and fungi quickly and with a high degree of efficacy.
Durability: Copper-nickel coins can survive at least 30 years in circulation. This is one reason why copper-nickel was chosen for the 1- and 2-euro denominations.

So, if they say it doesn't tarnish, they obviously haven't been looking at 20 p's! lol! 😂😂👍

There is some information on buried coins in these ...

https://metaldetectingforum.com/showthread.php?t=204569

http://www.njminerals.org/metaldetecting-haloeffect.html

Hmmm, that was very interesting reading , I've bookmarked a link on metals and souls, for later reading. I detect a lot I have an AV equinox 600, so that will be really helpful....just one more question, how do you bring them back to the original colour? I have some old Fracs that are also that colour.
😁👍

* Soils .

*Francs
( I'll get there in the end)!! 😂

you can edit your posts.
why do you want to return them to blast white? not that it matters, but the chocolate brown is an interesting unusual occurance, and a coin that has been chemically scrubbed is not that interesting.

Sorry, I didn't realise about the editing, I'm a technophobe and don't have any young people around me to help me out, ( when I first got a PC, it sat in the corner of the room for a week until someone showed us how to turn it on!! ha ha ha! not everyone has it going on! 🤪🤭🤤🤣

well, I don't use chemicals on coins and being that it's not a collectable coin and no one but me will ever see it again, I wondered if it would clean up. The old Francs I have dug up are also not valuable (other than to me ) I would like to see them silver coloured again. I think it's all down to personal choice. To be honest, I'm not lucky enough to find anything that's worth selling except maybe the jewellery I find, but even then, I'd rather keep it than sell it because I am a sentimental person. 🤎👍😁
Each to their own I suppose! lol! 🙃