Conservation Black Spots on Bronze/Copper

mrjason71, posted: "I have 1,000s of Lincoln Wheat cents and 100s that are BU. There are dozens with black spots. Black spots that EZ-est and the like will not remove. Are you saying "Most KNOWLEDGEABLE, EXPERIENCED folks can remove" these? Maybe you are talking about the occasional spot thats created from dandruff or spittle or organic material or something. Ive seen these dissolve away in EZ-est. Im talking about carbon spots. They are really sulfur spots. There are scientific studies on them. I think everyone knows what I mean. Sure some misidentify a spot here and there as a carbon spot, but these spots I speak of are common. You see them on coins in slabs. If most knowledgeable, experienced people could remove them, Im sure someone would mention how they do it on the internet."

Thanks for posting the link and calling me out!

I'm sorry to read about your coins. Unfortunately, AFAIK There is not one person in the world who can successfully remove actual BLACK corrosion spots from copper coins without leaving a trace. At the moment, some folks are working with lasers.

For those who know what they are doing, a coin's surface can be COMPLETLY STRIPED to remove SOME types of spots and then recolored. This is not very successful on original BU (red) copper.

PS Don't dip copper in EZ-Est.

PPS Notice that even the professional chemists in the link know what much of the "black" spots are and its causes but they left something important: HOW DO WE CONSERVE THE ITEM TO GET RID OF IT!

 

Log in or Sign up to hide this ad.

Didn't want to "call you out"! You are awesome and have been very helpful and have shared freely of your knowledge and experience. Numismatics is littered with these bastardized terms. Heck, "carbon spot" isn't even accurate and I've seen scientific papers calling it something as unscientific as "Black Spot on Bronze" lol. This preliminary debating over the meaning of a term reminds me of one of my other threads where we couldn't get anywhere for a while because I used the word "dip". Took two pages just to convince members I was talking about acid/thiourea dip.

Anyway, I'm talking about the real deal sulfur spots that can pop up right before your eyes...the kind of spot that makes you pass on the coin without a second thought...you can take a bit of brass-o and massage them away...and what an awful coin you have thereafter. Black spot or raw metal spot...which is worse? They're both hideous. Maybe the raw metal will tone and be less obvious. I've used erasers to eradicate them. Just literally erased them Same nasty raw metal hole.

I am not a chemist either. There MUST be something out there that will dissolve this sulfur (or whatever it is) without eating away the luster...especially flyspecks. I have a couple 1920s Unc Lincolns with flyspecks that just kill me. I would love to conserve them. I have the dates without flyspecks as well. Not a matter of just "buy another coin you like". Someone has PVC issue, we tell them get some acetone. If toning is black and hideous, dip it. Just would be awesome to have a "cure" for this.

 

The problem is that there are substances that can chemically break sulfur-copper bonds. The problem is that they will react more on the purer copper coin than on the bound copper - sulfur. Many older coins bear signs ( small pits) that they have been treated, probably with acid/thio dip or worse. After which they were probably bright pink, but if you wait 30-50 years they might retone enough to pass (Brown).

When a TPG guarantees they can remove ALL such spots, no matter the size, or money back. I might buy the aspect they have a secret formula no one has known but them. I think lasers have a better chance than chemicals myself.

 

Great stuff, desertgem--good food for thought. I'd like to find the right chemical--even if it's just to spot treat.

I remember buying a Dansco Lincoln Cent with Proofs album. I then bought an entire set of Memorial proofs off of a guy on EBay...as I removed each coin from its flip, these little black spots starting forming right before my eyes. Craziest thing I'd ever seen. I imagine the seller treated these with somethjng and then quickly got them in flips. I was just sitting in my room temperature living room watching TV. Like the measles they popped up. And the flyspecks I spoke of earlier--they are slightly raised and feel like I could almost scratch them off with a fingernail. Mostly there's those Cents that look to have had carbon spots for years the size of the point on a Sharpie marker. They look almost like the coin absorbed a black liquid. Those I might have to admit defeat with. They are "in" the coin. I hold out hope for those "on" the surface.

Sorry if I've wasted everyone's time. I hoped maybe lots of people would have lots of experiences with varying results and that it might be nice to have all this anecdotal info in one place. I'll keep up the search

 

The are several people around the forum , that thinks electrolysis can do it, but we haven't heard from them on this yet.

 

Really? Haven't come across that in my hunt. Like the homemade-power supply modification electrolysis? Or like some high tech thing? And would it be the sort of thing that nukes the entire surface of the coin? Toning and all?

 

I had a couple of otherwise nice coppers in my collection that had one or two black spots on them that bothered me enough to experiment. I've done a bit of plumbing on copper pipes and had some zinc chloride solder flux. I used a fine tipped artist's brush to apply a tiny drop of Zinc Chloride (available as liquid solder flux at hardware stores) to the black spots. It quickly dissolves copper oxidation, green oxidation and black sulfur spots. Wash off within a minute or less with warm water and carefully dry the coin with a soft cotton cloth without rubbing, just blotting it dry. There may be a spot of lighter copper exposed that can be blended in with mixture of powdered sulfur and mineral oil. But quickly remove this as soon as the color blends with the surrounding patina. Rinse the coin in acetone to remove remaining oils and handle with gloves. Try this on some junk coins before you try it on one in your collection. As another poster noted, if the oxidation is deeper than the surface, the zinc chloride will leave a noticeable depression where the oxidation had been. It does not seem to attack the copper, just removes oxidation but it stops the progress of copper "rust" or bronze disease. I haven't tried baking soda and distilled water, but apparently that can be used also for bronze disease - green verdigris, but takes longer and the coin is soaked in the solution for an hour or more. Google search "How to Remove Verdigris From Coins” (with the quotes).

 

Like @Insider said and @GDJMSP alluded to, about the only way to deal with spots on copper coins is to strip the coin and re-tone it. One of the things I have tried with some very limited success is to treat the spots on the coin with a reducing agent. I tried sodium sulfite. Not that great.

 

Wow. How easy it would be to keep this to yourself. To take the time to sit and put that together in that kind of detail for your fellow anonymous coin enthusiasts is just amazingly noble of you and I wish I could tell you how much I appreciate your generosity of information and experience. Thanks for replying. Hopefully those in the future who seek to be rid of these horrid spots will find your words before they deface a 100 more coins with experimentation.

I spent a few hours one day ripping various sized magic markers apart--pulling the ink absorbing cores out of them and running water through them until they were "clean" of ink. (I later realized you could buy these without ink in them!) It seemed to me that these would be the perfect implements to "erase" these spots with some unknown chemical applied to the tip if the chemical would not eat away the point of the marker. I put a little Brasso on the tip of the marker and found great control in abrasively "scratching" the spots out. I was left with such a God awful clean spot that I just abandoned the whole approach. This was probably the 20th such experiment.

Thanks again for the guidance. Off to the hardware store!

 

Thanks Kentucky! Did you find that the sodium sulfite only ate away at the sulfur spot?

 

Hey Tuck,
I still like @GDJMSP ‘s suggestion:
“.....Well, my suggestion has pretty much always been the same. If you have a coin with spots on it and you don't like the spots - then sell the coin and buy another one that does not have the spots. Just that easy - and it works, every single time.“

I realize this doesn’t help for VERY rare coins as you have to take what’s available but it does work well for commons. Don’t waste your time on trying to keep an undesirable coin find a nice one! Great advice from our site Overlord. Lol

Reed.

 

Only one thing bothered me a little when using sulfur to tone any part of a coin, including hiding repair, is that it does to many people fall in the realm of AT, artificial toning, even if it is just to hide a treatment.

 

I'll take altered surfaces over a carbon spot any day Id smash a slab to take out a straight graded coin with a carbon spot to alter its surface and id put it in a flip and sleep well

 

Judging what I see on a daily basis, it's a real shame millions of folks have taken up coin collecting.

 

I'm already a millionaire (in South Korean won), so I'm good.

I really would like to think that there's a solution, but I suspect there isn't going to be a fix for a lot of brown-spotted coins.

I'm a collector of South Korean copper-based coins, and their particular alloy is either 88% Copper, 12% zinc (known in metals industry as "commercial bronze") or 65% copper and 35% zinc (also known as "high brass"). I could swear, these coins have THE HIGHEST susceptibility to brown spotting of pretty much any coins ever minted! Get the storage of these coins just a little wrong, and you can expose them to the kind of atmospheric conditions or temperature swings to which these alloys are particularly susceptible.

 

You didn't read this from me but if it's that bad, I'd put lacquer or oil all over them until you are ready to sell. I keep my rough opals hydrated so they stay pretty.

 

We have to be carefull not to let our “old school” show to much there Insider. I haven’t seen anybody lacquer a coin in forever! Funny thing is IT WORKS! I found this picture of you in your coin conservation room. Enjoy!!!!
Reed.

 

Oooh here's one. On eBay...would love to break this thing out and fix it up. I don't know how this is Pf66--perhaps it's based on the low mintage/population. What a sin it's been allowed to deteriorate to this extent! Is this a carbon spot with verdigris around it? Weird to see black core with green halo...you can just see this thing grow and grow. Let's alter its surface and save this thing.