{"id":104,"date":"2012-11-23T03:56:20","date_gmt":"2012-11-23T03:56:20","guid":{"rendered":"http:\/\/userblogs.ganoksin.com\/binnion\/?p=104"},"modified":"2013-01-16T04:02:21","modified_gmt":"2013-01-16T04:02:21","slug":"copper-and-silver-rings-may-not-be-such-a-good-idea","status":"publish","type":"post","link":"https:\/\/userblogs.ganoksin.com\/binnion\/2012\/11\/23\/copper-and-silver-rings-may-not-be-such-a-good-idea\/","title":{"rendered":"Copper and silver rings may not be such a good idea."},"content":{"rendered":" $\"\"$ <\/a> The copper and silver ring before the test.\n

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This corrosion will not happen with rings made entirely of precious metals.<\/span><\/span> <\/strong><\/em><\/p>\n

Also this test is an accelerated aging test you will not see this level of effect in this short a time unless the ring was kept wet constantly, but it will occur. How fast 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 individuals rings that had copper or shakudo elements in contact with gold.
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W<\/span>hen you join two metals together in a ring beyond your aesthetic creation you also create something that under the right circumstances\u00a0 can destroy all your work.\u00a0 Two metals joined together in the presence of an electrolyte <\/a>create an electrolytic cell which 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.\u00a0 One of the metals will be more electrically positive or anodic and one will be more electrically negative or cathodic. The\u00a0 the difference between\u00a0 these poles is measured in volts. When exposed to the electrolyte the anode will dissolve and supply ions to the electrolyte. Just like electroplating or electroetching.\u00a0 The higher the voltage the greater the activity and the faster the anode will dissolve. Which metal is the anode and which is the cathode will be determined by their atomic properties but can be looked up in a chart called a galvanic series<\/a>. The higher a metal is on this chart the more noble it is and the more cathodic or negative it is. You will note the precious metals are at the top of the chart and that is why you will occasionally hear them referred to as noble metals.<\/p>\n

So what all does this mean? If you combine silver and copper as in the ring above you will have an electrolytic cell where the silver is the cathode and the copper is the anode . This ring in this test is mokume but it will not matter how the copper and silver are bonded, solder or rivet will still create an electrolytic cell.\u00a0 If you place it in contact with an electrolyte then the copper will give off ions to the electrolyte and dissolve.\u00a0 How fast is the next question, or at least that is what I wanted to know. 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 things like colorfastness of fabric dyes and the like. Another one is used to test for nickel release in jewelry items by the EU. So I looked up several of them and picked one that seemed to be both easy to make and not too concentrated.<\/p>\n

I chose 7.5g\/l NaCl, 1.2g\/l KCl, 1g\/l urea, 1ml\/l lactic acid with a pH of 4.57<\/p>\n

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.<\/p>\n $\"\"$ <\/a> The copper showed definite signs of etching in just 24 hours\n $\"\"$ <\/a> The crystal structure of the copper is clearly visible where the sweat solution has begun to etch it.\n