Pink Tone

I experimentally dipped these coins in a strong acid and they have acquired a pink tone. Now, is there any chemical reaction that could return them back to their state or cut down the pinkishness?

You've dissolved the surface nickel and are left only with the copper hence the coppery color. Why you would repeat that process 12 times (or worse chucking all off them in at once without even a test trail) is beyond me. And no destructive cleaning is never reservable, that's why we always advice never to clean coins … especially if you don't no your stuff.

Well, they were solid and dirty beyond comprehension so had to do something. I did recover some of them in good condition.

Next time use acetone 

I have but that's the worst cleaning experience I have witnessed, or perhaps I need to have the coins submerged into acetone for hours?

You can possibly retore them with care, put a small amount of sulphur powder (available from garden shop) in a jar of water,  shake it up and  suspend one of the coins in it, after a few hours the coin will darken. If you drop a coin on  the bottom of the jar then only one side will darken

Experiment to time it right, you can also put coins directly into the powder but then you can't see how fast they are darkening, they will go very dark indeed if left too long

Nice, I shall try that!

If Idolenz is correct in saying that the surface nickel is gone, there is no way to restore them other than replating them. They are destroyed for most collectors, theyre just novelties now.

FlyingRedPanda

If Idolenz is correct in saying that the surface nickel is gone, there is no way to restore them other than replating them. They are destroyed for most collectors, theyre just novelties now.

That is true but in some cases when the coin is extremely rare then most collectors would take it whilst waiting for a better example I did that with a kiao chao 10 cent coin 

Offa

FlyingRedPanda

If Idolenz is correct in saying that the surface nickel is gone, there is no way to restore them other than replating them. They are destroyed for most collectors, theyre just novelties now.

That is true but in some cases when the coin is extremely rare then most collectors would take it whilst waiting for a better example I did that with a kiao chao 10 cent coin 

any rare coin could would be worth more in its uncleaned state than in this cleaned/deplated state

I know but it is a way of getting the coin until a better example comes along