Is coin cleaning a big no?

I have some nice coins, which aren't worn or damaged, but are fairly dirty.
I'm wondering if I should clean them or not? I hear a lot that you should not clean coins, but polishing coins properly makes them look so much better.

Also, I have hundreds of Roman coins and older which I found myself (metal detecting). Don't really know anything about Roman coins, but about 50% of them it is impossible to see any detailing on it, and would love to know a bit more about them.

What's your take?

Personally, I would never clean any coin in any case. What'll happen when you clean a coin is; it will be clean and shiny, but what you are cleaning off is not just dirt, but its value.

I wouldn't even clean a coin with just water and soap, or just water for that instance. I know I might be a radical and that some forms óf cleaning could be "allowed", but I wouldn't clean a coin just because it's dirty.

Well, this is just me though  

New machined type coins I'll rinse in soap and water and pat dry with a cloth.
Roman coins are another story all together.  In my opinion you absolutely have to clean them  if they cannot be identified.  Otherwise it's just a round-ish chunk of metal that used to be a coin.

I use an ultrasonic cleaner. It works very well to remove dirt and does not affect actual tone - it has removed many blemishes in the past and has added much eye appeal to my collection.

Can you show us pictures of the ultrasonic cleaner effects.

Just done a small experiment using a sonic cleaner on a couple of coins (I only use this for cleaning my rc nitro engine parts but seeing this blog thought I'd try it on a couple old coins) any this is the outcome.
before pictures.



After cleaning



Let me know your thoughts please

Thanks for that, Tony! I think that the results are better on different metals. ?.

I think it depends if the muck/dirt is pitted into the coin or not, if it's pretty loose then you get a much better result. I will try a few more with different variants of metal and whether the dirt is pitted or not. Will post more pictures over this next week or so.

That's great. I think that we should have a section on cleaning!

OK, here are my 2 cents on the coin cleaning - though strictly personal.

First of all, there are several types of the cleaning and I have an impression that some people simply mix them up. In my view, cleaning may mean:
    - removing dirt, sweat, oil and other foreign substances from the surface of the coins (with the patina being untouched and unaffected)
    - removing corrosion (e.i. ugly corrosion spots) with the minimal effect on patina
    - partial or complete removal of the patina to make coins bright and shiny
    - removing earthy deposits and heavy corrosion from unearthed coins to make them recognizable    
And, of course, all this thing often overlap with each other and can make more or less serious cleaning very tricky.  

I personally do some very gentle cleaning (dirt only!) because for me a dirty coin looks - how to put it? - simply dirty and unpleasant. I do though restrict myself to removing lightly attached dirt only and I use a soft toothbrush with a drop of liquid dish soap - it cuts through the grease better than any hand soap and doesn't contain any skin lotion components which may deposit on the coin surface. I've never used an ultrasound cleaner but can imagine that the good one (especially the one designed for jewelry cleaning) would remove dirt gently and effectively and shouldn't affect the patina.
I stay away from any other type of cleaning simply because it may damage the patina - and the value - of the coin. Cleaning of unrecognizable unearthed coins is a completely different game, but I'll leave it to more experienced people to discuss.