Cleaning old copper coins

[Chilgrove]

I wonder if anyone else agrees with my thoughts about cleaning an old copper coin under the tap? Most or all of the drinking water in the UK is treated, quite correctly, using chlorine. I have personal experience of what chlorine can do to some metals and therefore I prefer to use rain water or distilled if there is any chance of the coin being interesting. It could be argued that the tap water is coming through a metal tap so there can be no danger of damage to metal but I still have this lingering doubt.

[LuckyB]

The amount of chlorine is miniscule, it will not damage your grotty already corroded copper coin, If it was going to cause a problem then you would soon know given all the copper pipes the water has to pass through to get to your coin.

Sometimes distilled water can actual be quite corrosive as it has nothing in it and to reach equilibrium it will dissolve any avalible metals, minerals and salts, in the middle east water produced from desalination plants often has some sea water added back in to "stabilise" it.

[Chilgrove]

Thanks LuckyB. I have the impression after cleaning dirty copper coins for many years under the tap that I lose some of the coin definition. However I do accept that doing so I cannot do a reasonably scientific test on the same coin using tap then rain water so I think I will just carry on using my rain water. I also find that not washing the copper coin at all but simply leaving it on a sunny window-cill can (appear to) enhance the definition.

[LuckyB]

I think it is the washing action (in any fluid) which is causing you to lose definition because it is removing some of the corrosion product which with copper alloys can retain some of the original surface details. The water softens the corrosion product and any brushing action will mechanically remove it (even with soft brushes). As you say leaving things to dry then picking off the dirt will help retain the corrosion product and is probably closer to the process used by profesional conservators for metal objects.

[KevinB]

The last few I have cleaned I used no water just a composite cleaning pencil on a dry coin it took a bit of time but pleased with the results. Just be careful with something a bit special. Four different bristles are available...