Shibuichi & Continuum™ Sterling Silver We are very excited to offer our newest metal combination, which is visually striking and durable; also the most affordable of our precious metal combinations. Given the high cost of gold, palladium and platinum it has been difficult to offer a high quality, lower cost mokume gane ring using precious metal alloys in the laminate. Our Damascus steel and blackened stainless steel have a lower cost than our gold or palladium mokume rings, however those metals don’t necessarily appeal to people who want a precious metal ring. By combining Continuum™ sterling silver and shibuichi we are able to offer a ring with beauty and high durability at a much lower cost than rings with other precious metal alloys.
What is shibuichi?
Shibuichi is a traditional Japanese copper / silver alloy. The name translates into English as “one quarter”. Shibuichi was often used to decorate a samurai sword’s handle and scabbard. Shibuichi has a nominal composition of 75% copper and 25% silver but can range from 5% – 60% silver. At 75% copper / 25% silver it has a pale copper color. In traditional Japanese work it was typically patinated to various shades of grey. I chose to use the 75% copper 25% silver alloy as it gives the resistance to corrosion and strength properties I was looking for.
What Is ContinuumTM Sterling Silver?
ContinuumTM sterling silver is a patented alloy from the jewelry supplier Stuller. It was developed to produce a sterling silver with improved hardness and tarnish resistance. Its use in our mokume gane in combination with shibuichi allows us to offer a beautiful, tough and long-lasting ring.
Color: While shibuichi is initially pale copper in color the alloy quickly will turn to a medium grey color with some copper tone highlights in daily wear. We will normally apply a treatment that colors it to grey before shipping. As it is worn it will develop a unique patina of grey with some coppery highlights.
Corrosion resistance: Shibuichi with its silver content is much more resistant to corrosion than I had initially thought. I conducted extensive tests similar to those I did on copper silver rings to see if this metal combination would be satisfactory for daily wear. This metal combination passed all of my tests. I feel confident in offering this metal combination as part of our precious metals mokume line.
Options: We can use this metal combination in all our ring styles and jewelry. Prices will be significantly lower than any of our other metal combinations that include gold, palladium or platinum.
In order to have a high contrast in the pattern, this metal combination will only be offered as etched.
No, 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.
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.
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/
Today I’m making a replacement ring for a customer. It is made from palladium 500 and sterling silver. This is a big ring: size 13.5 and 10 mm wide, It will be quite striking! Given its size and width you will see a lot of pattern.
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We have been struggling to find the right words to say during these stressful times. This pandemic has upended “life as normal” and we wish there was something we could do or say to make it better. Though all of our lives have been altered for the foreseeable future, life does go on. We will continue to post photos and information about our work and we are here to answer questions and work with you. We are available by phone, FB messaging, email and are working on video conferencing. In the meantime we thought you would like to see a photo of our “puppy” Hoshi who is now 8 months old and over 70 pounds! We hope this makes you smile…her antics certainly keep us smiling and laughing. This is her just after grooming before she could find the mud again! ... See MoreSee Less