An Old Problem That Was Never Solved

I remember you posted this coin. Like you said you don't have room for experimentation. The best advice I can give is to do nothing further. Why it might seem appealing to remove the "encrustation" you risk damaging the surface metal by removing the mass mechanically. If you attempt to use acids or the like you risk discoloration and or complete removal of the patina, neither option would be advisable. Enjoy the coin for its character and for whom is on it.
If you feel you must must must clean this coin further- you could soak the coin for a week or so in DI (deionized water) or distilled water. Allow the water to permeate the limestone. Give a quick dip (2-5seconds) in high purity acetone to dry the coin. Place the coin a sheet of Aluminum foil and bake the coin in your oven @ 375 F for 15 minutes. (Dont forget to pre heat). Then allow to cool to room temperature and gently poke at the lime with tooth pick or tooth brush. Hope this helps.

I agree. Distilled water is the mildest treatment you can apply. Just keep changing the water every couple of days and soak until the encrustation comes off. May take weeks.

You should be able to get it at any grocery store. Not sure why you would have any trouble finding it.

As your in the UK you might have a local 99p store?(http://www.99pstoresltd.com/index.asp) My local one sells 2 litre plastic cans of deionized water used for ironing down the household aisle.

"Nursery water" that they sell in the baby section is good also.

Given that it's limestone and therefore porous, wouldn't a soaking-freezing-resoaking cycle work? That shouldn't affect the original metal at all.

If it says that it provably has sone kind of coolent or anti freeze in it.

I'm not sure why most sellers have switched from distilled to deionized over here but seem to remember someone telling me its a cheaper/easier process to produce it? Never say to a chemist that they are the same thing thing but for what we use it for the difference is not worth worrying about, indeed DI water is often purer than distilled and that is a good thing. As close to H2O as possible is what you want and sadly tap water has all sorts of other things in it.

The car reference is for radiators and batteries but many people now say tap water is better for radiators as its not as 'hungry' for ions (can corrode from the inside) and most batteries are sealed. Its a bit pointless really unless you intend to keep your motor for a long time as its unlikely to do any real harm for about a decade. In the end your just choosing between death by corrosion or death by scaling! Anti-freeze needs to be added to it when it goes in the radiator and is not present before. I used to use it to refill fork truck batteries, much like household irons you don't want anything else in the water that could cause scaling as it evaporates.




Although pure it could still have bacteria in it, guess the manufactures are just covering themselves, I bet I drink worse at my local every weekend

Peter_thomas - it is indeed distilled, but a lot of stuff gets in it while its up there and un-distills it. The main worry I would have with that is acidity but it would most likely not make a difference