Tuesday, March 31, 2009

Jewelry Metal Chemistry 101

I've decided to break down my posts on finishes into several posts after realizing how much there is to say, so today, I'll be talking about patinas. One small piece of business to get to first tho!

Emma, one of my Etsy friends from the UK and owner of Emmateale Jewellery (http://www.emmateale.etsy.com) brought to my attention that in the UK, it is perfectly correct to use the term "carat" synonymously with "karat" when addressing the purity or finess of gold. So to all of my readers, I stand corrected. Thank you Emma! Now, on to the post!!

I’m sure all of us have had that same feeling at one time or another. You buy that special sterling silver or white gold ring and perhaps not such a long time later, you find that it’s losing its luster, darkening a bit in color, and if it has an intricate design, perhaps those little grooves are beginning to appear black. What’s your immediate reaction? I got ripped off? What a piece of junk? Time to have it cleaned to get rid of that gunk?

Maybe not. Sure, if you’re one of those people who loves the sparkle and sheen of a perfect finish on your jewelry, by all means, take it in and have it cleaned and brought back to its just bought beauty. But please don’t feel like you’ve been ripped off or that your jewelry piece is now a piece of junk. There are two truths, if you will, about metals: 1) In their natural form, they do not have the same appearance as the highly polished metals you find in most fine jewelry and 2) all metals, even the pure golds and silvers and platinums, will react chemically with their environment over time.

“Antiqued” or “oxidated” finishes on jewelry are becoming increasingly popular though, with the ability to create vintage looking jewelry through patination becoming an invaluable tool in metalworking for jewelry design.

Here are some unique and beautiful pieces from Etsy shops illustrating a variety of patinas.

Without going into a long winded chemistry lesson here, the metal in your jewelry (or for that matter, your silverware or copper pots or gold tea service) reacts to chemicals in the air, oils in your skin, heat, and chemicals it comes directly in contact with, either purposefully or through something as simple as eggs or vinegar or onions.

This chemical reaction results in the formation of a patina, a thin film formed on the surface of the metal, which alters the color of the metal. The process itself is referred to as patination or oxidization. I’m going to mention a couple of evil words here – tarnish and rust – which, from a chemistry point of view are other forms of oxidization, and actually can produce some lovely effects on metal IF, and it’s an important IF, the process that creates them in the first place has been stabilized and the metal sealed to prevent further corrosive processes. Yes, tarnish, rust, and patination all occur through corrosive processes and are all basically the same chemical process! The aesthetic appeal of the result is the difference – a good analogy would be like comparing a beautiful golden suntan to a lobster red sunburn. Same process – different results, different appeal.

Although it is possible to achieve patination on the pure forms of metals like gold, silver and platinum, it must occur naturally over a very long period of time, but it can also be forced through the application of chemicals such as sulphur or ammonia. In alloyed metals, it is often the copper in the alloy which is responsible for the patina that develops (called verdigris), although different alloys will contain different metals and therefore be able to produce different patinas. The Science Company has an extensive list of Patina Formulas on their website (note that neither they nor I are guaranteeing any results) http://www.sciencecompany.com/patinas/patinaformulas.htm . There are also a lot of simple homespun (more eco-friendly, less heavy chemical) methods of producing some patinas. Heat applied during processing of metals can produce an amazing array of patinas. My best advice is to leave it to the experts – many jewelry stores offer patination and many Etsy jewelry designers are truly experts in the process!

One important thing to note about patinas is that many of them can be toxic and therefore it is wise to make sure that the metal that has been patinized has also been appropriately sealed. Standard methods of sealing include application of a lacquer or wax (Renaissance wax is an industry favorite).

There are also a number of “paint-on” faux patina finishes that are being used in the jewelry industry to simulate a real patina. While many of them are beautiful, keep in mind that these finishes do not bond to the metals at the chemical level, leaving them much more vulnerable to wear and tear than a natural or chemical produced patina.

For those of you who appreciate a variety of jewelry finishes, consider patinated jewelry. The richness of the colors, the unique luster of the metals, and the beauty of the look in general can lend much to your overall fashion style.
Tomorrow I'll be doing another piece on finishes and also touch on some information about the types of wire used in jewelry making. Hope to see you back here soon!

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