I have a really strange issue I need advice with. I had some of my coin collection loose in a small box temporarily as I did some home renovations. I had the box on a shelf where I also had a container of car radiator fluid (stupid I know, but it was temporary and they weren't near each other). Well at some point the rad fluid container cracked and the fluid spread across the shelf and my box of coins soaked it up. Here's the issue. Most of my copper tokens from the 1800's have now got a sticky green tint to them. My silver coins seem to be ok. I was wondering if you know any safe way to maybe take the green tint away without ruining the original patina of the coin, or doing as little damage as possible? Is there something I could soak them in over a period of time that will draw it out? I've been a collector for years and I know you should almost never clean an old coin, I'm just not sure what to do. Any advice would be amazing at this point. All I've tried is gently rubbing them with a dry paper towel and some of the green is coming off, however also some of the patina on certain coins. I didn't want to try anything else until some more research was done. I've been reading through some threads on this forum about cleaning coins in acetone, would that work here? Thanks!
Welcome to CoinTalk! First, stop rubbing with a paper towel. Yes, that's guaranteed to ruin any coin that isn't already ruined. Second, since radiator fluid is water-soluble, soak the coins in distilled water. This may do the trick. While you're doing that, read on: I'm not sure there's anything in radiator fluid itself that would damage your coins, but it might have picked up something else (from the box or elsewhere) that was harmful. "Sticky green tint" sounds like damage from PVC, a soft plastic with components that can react with coin metal (especially copper). If distilled water (soak and rinse) doesn't solve the problem, it's worth trying acetone; that can remove some plastic-related substances that water won't touch. There's also a product called Verdi-Care, invented and sold by a member here (@BadThad), that can give excellent results removing verdigris (green corrosion) from coins that contain copper. Whatever you do, don't rub the coins. Under some circumstances, you may end up dabbing the coin with a wet cotton swab or microfiber cloth, but rubbing, especially with regular cloth or tissue, will almost always produce permanent damage. Good luck, and please check back in -- I'd like to know how it goes, and there are a lot of people here who are in a better position to offer specific advice than I am.
Given the composition of ethylene glycol as a very polar organic substance, I suspect acetone will be quite effective at removing it. As @-jeffB said, though, just plain water should be pretty effective on its' own.
You don't say what kind of coolant it is. There are several formulations on the market and some would warrant special consideration, if your rubbing them hasn't already shot you in the foot.
If all else fails, you might try soaking your copper or bronze medals in 100% pure virgin olive oil. This 1836 French medal had (dried) green crud all over it until it was given repeated soaks in olive oil. Chris
Thanks Everyone! Yes I know the coin rubbing was bad. I only did that to a few coins before noticing what damage I was doing. I also tried washing one with warm soapy water, but that made no difference other than it was no longer sticky. Still green though. I have no idea what the name brand was on the coolant, but it was the orange kind. All the labels had been ripped off at some point. I will try all methods you've suggested to me on some of my less valuable coins and see which works best, then report back here with the results. Thanks again.
Well I thought I'd update this as I've made some pretty good progress. It seems the distilled water worked best. It seems to take away the green and the stickyness without harming the patina. Thanks! I also tried some coins in acetone, but although it did take away the green, it also left my coins looking hazy. I only did a few coins in this as a test. Maybe I left them in too long. Oh well, the distilled water has saved the day. Thanks again everyone for the advice.
If the antifreeze was orange, it has OAT (organic acid technology) corrosion inhibitors. OAT compounds aren't orange; but an orange dye is added to signal their presence. Antifreeze is quite a witches' brew. Although most of them are based on ethylene glycol as the main ingredient, they contain dye, corrosion inhibitors, and lubricants. Ironically, it's the corrosion inhibitors that are likely to be a problem for coins. Some of these compounds are selected for their ability to bind to metal and form a protective layer. That's great for your radiator and engine block; not so great for coins. A distilled water soak and rinse, followed by an acetone soak and rinse, and final distilled water rinse is about the best you can do. Cal
The hazy look happens to copper after acetone. It removes all the oil from the surface and takes away the glossy look. Don't worry, it didn't harm them, just gave them a "dried out" appearance that I've seen dozens of times. A little verdicare will rehydrate the surface safely, if you want to buy a $10-$15 bottle of it from one of our members here. It's available on eBay.
A lot also depends on what kind of coins they are. Ancient collectors tend to go all buggy about patinas, whereas world and US collectors are a little less committed. Now that is not to say anything about toning. What kind of coins?
Cal is right about the corrosion inhibitors binding to metal. Maybe this is why you see the hazy appearance after soaking in acetone (This is only a guess). Removing these could be tricky and beyond the ability of many "shade tree numismatic chemists" to provide good advice. I would be careful trying anything beyond the acetone and distilled water unless you know what was in the antifreeze and can get an opinion from a good chemist (there are some on CT) as to the correct solvent to use.
I like that...seriously though, for a situation such as you seem to describe, the only safe course to follow is water, distilled water and acetone (perhaps a side trip to 91% rubbing alcohol). Alternate among these until the coins are clean - finish up with either pure acetone or distilled water. Particularly if the coins are Unc, AU or proof. If less than this, a toothbrush brushing won't hurt (ignore this if any are $1000 dollar coins). Finally, copper, silver or gold is relevant.
Well the coins weren't anything super expensive as far as coin collections go. The coins I had the most issue with were old Canadian tokens from the early to mid 1800's. It's not that any one coin is worth a whole lot, but the fact that this affected about 40 coins of my collection was upsetting. Like I said though the distilled water seems to be working fairly well. Thanks again for all the help everyone. It has really saved my bacon.
If and when I ever clean a coin I use the softest small paint brush and brush from the middle to the outside rims. Always use distilled water and mild dish washing liquid.
