Pieces of anodized titanium

When Morgen and I got married, most of our wedding guests came up to us and said things like “Congratulations!” or “Enjoy your honeymoon!” One of our friends, however, on seeing our titanium wedding bands, cautioned us gravely, “Avoid electrified salt solutions.” That’s one of the strangest things anyone has ever said to me. Not knowing how else to respond, I assured him that we would—in fact, I think I can safely say that I have made a lifelong practice of avoiding electrified liquids of any kind. But I always wondered about that odd warning. Years later I ran into this friend again and asked him what the deal was—what terrible fate would have befallen us, or our rings, had we encountered an electrified salt solution? He said it would permanently alter the appearance of the ring, and sent me some links to photos of titanium that people intentionally treated in this way in the name of art.

The examples of titanium jewelry, sculptures, and other artwork in the pictures were lovely, with intricate patterns in rich, vibrant colors. Our friend had mentioned that one could obtain a wide range of colors using this process, and sure enough, artists seem to use every color of the rainbow. But what I found most interesting about all this is that all the colors are essentially an optical illusion.

Just Add Water (and Electricity)

Any metal, given the right conditions, will oxidize, which simply means reacting chemically with oxygen to form a new compound. When iron oxidizes, the result is iron oxide, which we all know as rust. Some metals are less prone to oxidation than others—aluminum and titanium, for example, do not readily oxidize in air. But with a little help, they can form very thin oxidized layers that, unlike rust, actually protect the metals from further damage. One way to cause oxidation is to put a piece of metal in an electrolyte (an electrically conductive solution) and apply electricity—the negative electrode, or cathode, is placed in the liquid and the metal being treated is connected to the positive electrode, or anode. This procedure is therefore known as anodization. Chances are, if you have any aluminum products in your home—cookware, for instance—they have been anodized. The aluminum oxide coating thus created is quite hard and prevents the aluminum from reacting with, say, tomato sauce.

You can do the same thing with titanium (and several other metals). Titanium oxide is clear, but when light shines through it onto the reflective metal surface and then bounces back, the titanium oxide refracts it. The result is the appearance of color—even though the metal itself is whitish gray and its coating is transparent. So without dyes, paints, enamels, or any other materials besides titanium and oxygen, anodized titanium products can be made to look outrageously colorful.

The Anodizing Solution

Although some electrolytes are salt solutions, most common salts produce poor results when it comes to anodizing titanium. Better results come from an alkaline solution of something like baking soda or trisodium phosphate (TSP), or an acidic solution (think Coca-Cola). The color obtained is mainly a function of the amount of voltage applied to the metal; the more voltage, the thicker the layer of titanium oxide produced and the more refractive power it has. Some shades require that the titanium be etched with an acid before anodization, and some (like pure black) are impossible with anodization alone.

Artists whose medium is anodized titanium have developed numerous clever techniques for controlling the thickness of titanium oxide deposits with great precision. In this way, they can create nearly any imaginable design. I’ve seen framed titanium “prints,” titanium earrings, pendants, and pins, and all sorts of standalone titanium sculptures. There are also some anodized titanium rings, but because rings are subject to a lot of abrasion, which can wear off the titanium oxide coating, they tend to dull and lose their color. Of course, if my hand just happened to fall into an electrified salt solution and I managed to survive, it’s comforting to know my ring would eventually return to its original color. Who needs that kind of stress in a marriage?

Note: This is an updated version of an article that originally appeared on Interesting Thing of the Day on February 16, 2005.

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