Corroded copper and silver ring with the copper almost completely goneNo, I will not make you a copper & silver mokume ring.
It is not because I don’t like the color contrast. I love the color contrast that copper alloys have with silver in mokume gane. The original Japanese work in mokume gane was almost all done in copper alloys and copper alloys with silver. Those strong color contrasts are one of the things that originally attracted me to mokume gane.
It is not because it is cheaper than the precious metals that are in most of my rings. The rings I make are labor intensive. The mokume process is very time consuming and exacting. We hand make every ring for a customer; we do not mass-produce or machine-produce these rings. I and my studio assistant make every piece of mokume gane. We cut, clean, stack fire and forge the mokume billet from the individual sheets of metal. Most of the metals I alloy, cast, forge and roll into sheet myself to get the color and working properties I want for my mokume gane billets. Almost all the rings we make are intended to be wedding or engagement rings. They hold great significance for my customers as the visible symbol of their love and commitment for one another. Because of this I strive to make the best mokume gane rings we can possibly produce for each and every person who has entrusted us with the job of making his or her ring. So even if we were to make a copper and silver mokume gane ring it would not be inexpensive due to the time and care we put into each and every one of the mokume rings we make.
The reason I will not make you a silver and copper mokume gane ring is that they self-destruct. Copper is a base metal as opposed to being a noble metal. In chemistry, noble metals are those that are resistant to corrosion and oxidation in moist air. The noble metals are gold, platinum, palladium, silver, iridium, osmium, rhodium, and ruthenium. In and of itself copper being a base metal is not the problem. By itself when worn on the skin copper will corrode and turn your skin green; this is a nuisance but many people are ok with these phenomena and wear copper bracelets or rings. The problem comes from a physical property of metals: galvanic corrosion.
A galvanic cell is what is created when you connect two different metals in the presence of an electrolyte. It makes an electrochemical cell otherwise known as a battery and electrical current will be produced. So what has this got to do with a copper and silver ring? There is a battery formed by the copper and silver when the ring gets wet; salts on the skin, lotions and soaps or other substances in the water create an electrolyte. This current will flow from the more negative metal to the more positive one. When this happens, galvanic corrosion causes the more positive metal to dissolve or corrode into the electrolyte and the more negative metal is inhibited from corroding. Copper is the more positive metal in the copper silver pair and it begins to dissolve every time it gets wet. The speed with which this happens is controlled by many variables and it is impossible to predict how fast the process will be for any individual. However it will happen! Any ring made from a base metal (such as copper) in contact with a noble metal (such as silver) will corrode. Rings made from noble metal pairs (such as gold and silver) will still form galvanic cells but their resistance to corrosion (nobility) keeps them from being dissolved into the electrolyte.
When I first started making mokume gane rings I did not understand this. I made rings with gold and shakudo and with silver and shakudo. Shakudo is a traditional Japanese decorative copper alloy that is about 95% copper with the balance being gold. It takes on a dark black color that is very striking when laminated to high karat gold metals. Another artist told me about galvanic corrosion and I began to research it. After learning more about it I decided self-destructing rings were probably not a good idea so I quit making them. But over the years I have had the occasion to see rings that I had made where this corrosion was very obvious.
Top photo after about 18 months of wear. Bottom photo the same ring when it was brand new.The experimental ring.
To illustrate the problem of galvanic corrosion I decided to make a copper sterling silver ring and perform an experiment with it. I published my experiment on another blog on a jewelry-making site. Since we often get requests for copper silver rings I thought I would share that post here as well.
Since this was first posted several people have somehow assumed this is a problem with all mokume gane. It is not! The corrosion will occur only if one or more of the metals in the ring are a base metal and two metals are connected in a wet environment. This corrosion will not happen with rings made entirely of precious metals. Rings worn daily are the jewelry items that will typically be affected due to the fairly constant wetting of ones hands.
This test is an accelerated aging test so you will not see this level of effect with normal wear in this short a time, but it will occur. How quickly will vary widely with the individual and their environment. I have seen this level of corrosion over the period of a couple of years on some individual’s rings that had copper or shakudo elements in contact with gold. Two metals joined together in the presence of an electrolyte create an electrolytic cell that is in essence a battery. In a ring the electrolyte is provided by the water you constantly expose your hands to through washing, sweat, swimming etc. One of the metals will be more electrically positive called anodic and one will be more electrically negative called cathodic. The difference between these poles is measured in volts. When exposed to the electrolyte the anode will dissolve and supply ions to the electrolyte. The higher the voltage the greater the activity and the faster the anode will dissolve. The higher a metal is on a galvanic series chart the more noble it is and the more cathodic or negative it is. The precious metals are at the top of the chart which why you will occasionally hear them referred to as noble metals.
So what all does this mean? If you combine silver (noble metal) and copper (base metal) as in the ring above you will have an electrolytic cell where the silver is the cathode and the copper is the anode; the copper/anode will corrode.
No matter how the two metals are joined (bonded as in mokume, soldered, riveted), it will always create an electrolytic cell. When copper is placed in contact with an electrolyte the copper will give off ions to the electrolyte and dissolve. How quickly is the next question, which is what I wanted to know. When copper is placed in contact with an electrolyte the copper will give off ions to the electrolyte and dissolve. I wanted to know how quickly this happens so I set up a test to find out.
Believe it or not there are defined standards for test solutions to simulate human sweat for testing properties such as colorfastness of fabric dyes; the EU uses another one to test for nickel release in jewelry items. I looked up several of them and picked one that seemed to be both easy to make and not too concentrated. I chose 7.5g/l NaCl, 1.2g/l KCl, 1g/l urea, 1ml/l lactic acid with a pH of 4.57. I placed this mixture into a beaker at room temperature and suspended the ring in it with nylon fishing line. I thought I would check on it once a week or so but I took a peek at day one to see if anything had happened. Much to my surprise etching had become visible in only 24 hours.
Day 0: The experimental ring, highly polished, non-etched in sterling silver and copper before beginning the test.
The copper showed definite signs of etching in just 24 hours
Day 1: The crystal structure of the copper is clearly visible where the sweat solution has begun to etch it.
Day 3: So I decided to check back in another 2 days. At this point the etching was quite pronounced.
Day 7: The ring was severely etched.
Day 7 close up: In fact in some places the copper had been totally eaten away. Day 10: The end of the test.
Day 10 close up: At this point the copper rich areas of the sterling were beginning to be affected by the solution and in many places the copper was totally gone. In another few days the ring would have fallen apart. Quite beautiful in a very distressed way.What should you take away from this? Copper-silver rings will corrode/etch over time….it may take months or years but it will happen. It often starts subtly so it may be a long time before you notice. However if you want a ring that will last a lifetime buy a ring made from a combination of noble metals (platinum, gold, palladium and/or silver).
If you would like to see some of the rings we make that will not have any issue with galvanic corrosion take a look here https://mokume-gane.com/rings/
Thanks for reading,
Jim
I am curious if the ring were to be sealed with a clear polymer coating. That should keep it dry. Is there any reason not to do (something like) this?
Unfortunately coatings are not really suitable for the wear that rings receive. No coatings can stand up to the rigors of day to day wear, for other jewelry items coatings can work but may not be absolutely necessary.
Can you purposely galvanize/corrode much of the copper out of the ring and then fill the gaps with a clear epoxy?
The epoxy would quickly get scratched up and probably not end up looking very good.
It would be extremely tricky to pull off (possibly) but could you use glass as a coating instead of a polymer?
Probably not a realistic task.
A little off base here, but I’ve been familiar with the galvanic stripping action of dissimilar materials for quite a while. When my windmill quit pumping they pulled the sucker rod and galvanized drop pipe. There were holes eaten all the way through the drop pipe! The bronze pump head and the galvanized drop pipe didn’t like each other – especially in my highly mineralized water! (Can’t bathe, wash dishes, flush toilets or grow anything with it! Makes pretty good adobes….)
wow this has been very interesting to read and learn about. thank you so much for sharing ur findings.
Thank you so much for the information! Would there be a good alternative to copper that contrast well with silver? Something that is not as precious as gold.
Alternatively would shibuishi be better than regular copper in terms of longevity?
There is not really any substitute that is not a gold alloy. There are only two colored metals copper and gold, all the others are some shade of grey. Silver is the closest to a pure white but it is also slightly grey. So alloys that have a color other than grey are made using either gold or copper or both. Any of the traditional Japanese copper alloys like shakudo will have the same issue as copper in that they will readily dissolve when used in a ring. Other types of jewelry are generally not a problem but rings are so exposed to water that electrolysis is a real issue.
So what about an alloy of gold and copper or silver and copper? Still the same effect?
Depends on how much gold is in the alloy, 14k or better will resist corrosion. Red gold is the only real substitute for using copper in rings.
I read with interest your article. Are you saying then that 9k gold as we use in New Zealand would also corrode the same. Have you tested this as I thought it would be fine as much jewellery here has silver and 9k gold even before the advent of mokume gane. I was hoping say shakudo (4%gold) and say 3k (12.5%gold) would be alright. Your comments appreciated. Regards Brian Dodds
Yes 9k would corrode if you were to join it to 14k or 18k. It would be much slower than the copper corrodes but yes it will. Basically any alloy of less than 50% weight gold or lower than sterling silver will corrode if paired with a more noble metal. So 9K against shakudo the shakudo would corrode, 18k against 9k the 9k would corrode.
Thanks James I now see you already answered my question before. Just learning how this blog system works
This is a very interesting article, and it stands to reason why one wouldn’t want to make any items with this combination.
I’m wondering, if silver is often alloyed with copper to make sterling why this doesn’t happen then. Maybe I missed it in the article, and I’m sure it has something to do with science and the way it is alloyed. In that case, can something be done differently to the copper, so this doesn’t happen in the Mokume gane process?
Also, can mokume gane be achieved base metal to base metal
Thanks so much for the information…invaluable!
It actually does happen in sterling but it gets more complicated to describe. If you look closely at the 10 days picture you will see pitting in the surface of the sterling. Sterling is what is called a two phase alloy. At room temperature there are two different crystal structures in sterling one that is mostly silver with a tiny bit of copper in it this is the alpha phase, the beta phase is mostly copper with a tiny bit of silver in it. Because there is way more silver than copper in the mix sterling is mostly alpha phase with small bits of beta phase in it. The beta phase will corrode just like the copper in the experimental ring. It is just so small an area you don’t normally see it. Unfortunately there is no magic trick that can be used to fix the galvanic corrosion issue, it is a property of the basic atomic structure of the metal elements. This is why steel is coated with zinc to “galvanize” it. The zinc is the more anodic (+) metal and it will preferentially corrode instead of the steel.
Base metal mokume is fairly common but not suitable for rings because of the corrosion issues.
Bronze and silver? Will that just be a slower degradation?
It will be very similar to copper silver, probably not noticeably slower.
I am a jeweller from New Zealand. We mainly use 9 ct gold and combine it often with silver with many rings long before Mokume gane became popular. I never heard of the silver or the 9 ct gold dissolving with those rings. Do you think there would be a problem with Mokume gane if using those combinations? Have you ever done a test whether on this combination. I was hoping may be 3 ct gold (12.5% gold) would be all right. Even hoping Shakudo (4% gold) would be all right. Look forward to your comments. Regards Brian Dodds
I can definitely tell you shakudo will not work, I am very doubtful 12.5% gold will fare much better. We don’t use 9K here but I do know it suffers from some corrosion issues as does 10K. But it is real easy to test. Solder two pieces of sheet back to back with one being the alloy under test and one being the highest karat gold in the desired laminate and suspend the resulting plate on a piece of nylon fishing line in a solution of 1 liter of water with 7.5g NaCl, 1.2g KCl, 1g urea, 1ml lactic acid. This is an artificial sweat solution. Pull the plate every day and see what happens. The degree of corrosion will be your guide to how much damage you are likely to see in use.
could always just add a liner inside the ring as many jewelers do prohibiting contact of mokume and skin, thus leaving mokume outside and visible for looks and liner inside the ring for practical function.
Unfortunately a liner will not inhibit the corrosion and in some cases can make it worse. For example the use of a gold liner will make the corrosion happen even faster. The corrosion happens because the different metals are in direct contact with each other and exposed to water. This cannot be avoided except by never allowing the piece to get wet. Since we are talking about rings that are worn daily that is not really possible, even the moisture on your skin will allow the process to occur.
Woah, I learned something new today! Came here from Pinterest and this was a real fascinating read.
“Quite beautiful in a very distressed way.” – I was thinking the same. Is it be possible to make a piece of jewelry so that the copper would corrode but the noble metal would still be wearable, or does everything fall apart once the copper goes?
I am no jeweller and stumbled upon this article for completely unrelated reasons, but I must say: the final result (with copper almost completely corroded out) is strikingly beautiful. If there is a way to keep the ring structurally sound on that stage, it can make a great new technique capable of producing very exciting designs. I’d pay top money for something like this.
I know, if there were only some way to stabilize it.
Could filling the etched out line with niello save the design and stop the corrosion?
I guess the only way to create a stable design that holds the shape of what the silver looks like after the copper corrodes is to have laser etching of the spirals.
Yes except the ring is beginning to fall apart. The copper and silver are in parallel layers if all the copper goes away all you end up with is pieces of silvery not a ring 😟
Just thinking out loud, what about cutting a groove around one of the band edges to inlay a wire of even more reactive metal like zinc the way sacrificial anodes on boats work?
I think it looks awesome after the copper is gone!!!
What a great article. This gave me such in-depth insights into the workings of base and nobel metals. I do wonder, after looking at the etched ring, is it possible to use the natural etching of a combined base and nobel metal to make a piece of jewelry? Because the ring, after 10 days, looks soo sick with the deep, almost canyon like markings etched into it. Maybe in a way where you would let the coper etch for 5 days, and then use a dissolving solution to clear out the remaining coper? Or does that make the ring unstable?
Would it be possible to electroplate the weathered ring to retain the etched grooves ( of course losing the color difference) and stop the corrosion?
Untill you managed to scratch through the plating, then the corrosion would continue and eat under the plating and it would peel off.
my first exposure to mokume gane was 1990. very very little of it was gold based. it took a knife maker doing very large billets in a short time to really hook me on the process. it was married metal before that. I understand why making higher quality rings, that last forever, is important. but i wonder if the harsh wack on the nose for those learning other methods is good for the experimentation process. then again..im always amazed at the mokume like process in paper, wood, steel, clay. the lamination of materials for variation in color or texture is awesome. 1990 the jeweler i was learning metals from viewed mokume as stupid. it was only a thin layer of varied metal with a base metal back. so we just didn’t try it. i beat my head on that way for 5 years. before going to a knife maker to learn the trick. i understand it doesn’t work for rings. but the process is beautiful and wonderful what ever metals or end product you choose. even stainless lol
It works great for rings as long as you steer clear of using base metals in the laminate 😀
This is a fascinating article, but confused me. The base metal vs noble metal makes total sense to me, but as gold / silver are to weak to be used pure – there is always an alloy present. Now as you mentioned – if you used 9ct and 14ct together the 9ct would be worse off due to the higher alloy content. But what confuses me is the simple plain 9ct rose gold band, if it is a mixture of copper and gold – does the ring start to weaken over the years? Or does the chemical/battery effect only happen if a pure base metal is present and in contact with an alloy. I’m not a jeweler/chemist by any means – so I apologize if this is a silly question. Just very curious.
The short answer is yes there is some corrosion in low karat gold alloys. It shows itself as tarnish or discoloring of the gold alloy surface. Typically it is not a big deal though.
But, what about ring where copper and silver is mixed, are they self-destruct too(I mean silver rings with copper details)??? Thank you in advance!
Yes
What about pairing brass and copper, obviously brass being an alloy of copper, i assume corrosion wouldnt happen in this instance?
The corrosion will still occur, but more slowly as there is not as much difference in galvanic potential.
My husband and I fell in love with mokume, and made our own wedding rings with it, lining the inside with silver to avoid any green skin issues. After 2 years of continuous wear, however, the copper has all but disappeared. The grain was very fine, so the canyon-effect is not very pronounced. It pretty much looks like a silver ring with deep scratches, less visible because there’s no contrast. I was hoping for some ideas for putting copper back in the grooves, or creating contrast somehow, but I didn’t realize this was an expected side effect of putting copper and silver together.
If you happen to have any ideas for making the best of this situation, let me know.
Unfortunately there is no solution to the corrosion issue and I am sorry to say not any way to repair it. This is the reason I don’t make copper / silver mokume gane rings.
A combination of gold 14ct and argentinium might be a good mokume combination.
What do you think?
Argentium has too many drawbacks in my opinion. I know some folks love it but I am not one of them.
Very interesting. I find the corroded ring beautiful – if only the process could be arrested before the thing falls apart! I myself wear a copper/silver/brass mokumé gane wedding ring (24 years and counting). My jeweller, Susi Hines, made it with a kind of U-shaped silver lining, so the mokumé section effectively fits into a shallow trench, backed and bordered by silver. Perhaps this is why it has survived or does the brass prevent the corrosion effect? I can see a couple of small areas that have corroded, that’s all.
The corrosion varies depending on many factors. Often the effects are hard to see because you see it every day and don’t really see the changes.
this article and the comments are wonderful!! please keep up the scholarly explanations of stuff!!!
Hi
I means that gold plating brass om fashion jewelry is a complete nonsense?
thks
dan
Not really, on anything but rings there is not really an issue with galvanic corrosion. It is the constant exposure to water that rings experience causes the problem. That is why there are not many companies that produce rings that are gold plate over brass or copper alloys. Gold plated rings are normally made of silver not copper alloy .
Thank you , it is very interesting , is there any effect due to the way the clients are taking care of their rings?. for exemple I know that most of french women never take their ring off and keep them for washing , taking a bath etc.. in opposite of most of german women who take them off.I think clients should know about that problem and in france or even in US Isee many of nice brass rings which are gold plated from reputated brand names such as Dior, Channel. may be those manufacturer are aware of it and gold plate with at least 20 microns their brass rings.
I am having a box made as a wedding present to contain several family heirlooms: a gold wedding ring, a watch of silver (maybe platinum but not sure), earrings of gold, pearls, & silver. These will sit on a platform of wood (oak), and the sides of the box will be made either of aluminium or of copper, with a wooden top. Will the sides of aluminium or copper condemn the precious heirloom to a death from corrosion?
RED
No the metals on the sides of the box will not cause corrosion problems. However the wood and some wood finishes may emit fumes that will cause the silver to tarnish. You may want to line the box with tarnish resistant cloth.
Curious, how does this work with the Shibuichi line you have?
https://mokume-gane.com/product-category/shibuichi-collection/
Do they exhibit the same issues you mention in this article?
Hi John,
The silver content in the shibuichi prevents the galvanic process from removing the shibuichi. The copper rich areas on the surface are eaten away until there is enough silver on the surface to halt the action,it forms a passivated surface of silver. This is why the shibuichi goes grey in color from its natural pink.
Hi, I stumbled across your article whilst looking for reasons why my copper superconductor ring has started to become very dark in colour after only 1 day of wearing it next to a silver ring on the same finger (2 separate rings) my question is, if I was to wear a thin band of tungsten carbide separating the 2 rings would galvanic corrosion still happen?.. thank you
Mark, the copper niobium superconductor material will have galvanic corrosion issues all by itself. Niobium is more noble than copper So when exposed to sweat the copper will corrode at an accelerated rate. As for a tungsten carbide band as a separator, it will not do anything to change the galvanic corrosion issue with the copper/niobium superconductor material.
This was an incredibly interesting read, I learnt so much! Thank you to the author and all those who asked questions
Our mokume-gane rings, made by George Sawyer in 1998, are white gold, yellow gold, and red gold, if I recall.
After 23 years, I see a very slight corrosion of the red gold: it looks almost like your “Top photo after about 18 months of wear” but with about half the depth of decay seen in the photo.
We work on computers, so the rings see only normal hand-washing: no jungle environments. We’d like the rings to last another 23 years, so … any recommendations?
I really can’t comment on George’s rings as far as corrosion issues go.
That’s cool, thanks.
This is some invaluable info that you cannot find anywhere. Still, what if you ask for a rhodium polish, wouldn’t that protect the jewel?
Rhodium is a plating process, it would coat the whole ring with a layer of white rhodium which defeats the idea of laminating different colored metals. And eventually the rhodium would wear off and the corrosion would continue.
This article – and the follow-up comments – continue to be a fantastic resource. Thank you for this!