Toning

Hi, I recently bought some coins from a private collection. Several have an unnatural coloration. For example, cu-ni coins look like oil does on water, almost a rainbow of colors. Does that mean the coin is valueless? Is there any way to clean it? It does not look good to me.
Paul

Ok...they might have developed this toning naturally...however it is more likely that this has been added to the coin artificially to add value...I hope you didn't pay too much. I doubt it can be undone.

I bought them by the pound and did very well. I guess I will throw them away. Thank you.
Paul

Don't be too hasty! Let's see some scans or pictures of what you are talking about.

Hi Paul

Toning is a term to describe the tarnish or light patina that forms on the surface of the metal due to exposure to environmental agents or toxins.
It can be natural or done intentionally, but artificial toning is more complicted. Toned coins normally have more value and it strongly reccomended not to clean it, simply this rainbow toning is on molecular level, so suggest just leave it as it is

These will give you an idea.
Paul

One of my relatives once found a batch of old coins in a cupboard, from around the world but mostly British. Looking through them, I came across a 1961 florin in uncirculated condition. It had a beautiful multicoloured patina, and it is now the gem of my British copper nickel, just because it looks nice.

So, if the toning makes the coins look nice, then they are worth keeping.

(I think the best of the lot in the photo is the NZ 50c)

Alright then, and thank you.
Paul

Could be they were improperly stored, perhaps they became contaminated by being stored in PVC, exposed to heat, humidity for too long.. Someone may even have tried cleaning them to correct this, thus making them look rubbed and producing what looks like oily stains.. I've seen and experienced this before..

There are different ways a coin will tone, but if it looks un-natural or pasty white, bluish green, or rainbow colored oily stains, particularly on copper coins, that is a red flag..  On the bright side sometimes they develop into some attractive tones... I would not throw them out though...

I'm afraid I'd scrap coins like that pretty quickly not even worthy of the swapping pile. It's definitely poor storage and lots of moisture.

I wouldn't throw 'em
Away they will have a value to someone ! Just let them know they are tarnished.

My friend has really  bad sulfer in his water at his house and just this alone turns ordinary piles of change into this rainbow toning in a matter of days. Strange thing so it must have some effect in the air I'd imagine - so it could be a number of things doing this to those coins not just necessarilly poor storage or fraud. I once had a Soviet Union mint set UNC that did this also, and they had never been touched but got a crack in the casing after all them years in an airtight environment; soon as they hit the air they decided to start corroding.

Half the coins in Florida look like that