Monday, 18 February 2013

Process of Anodizing in Jewelry Making

Anodizing titanium - Etch the titanium by immersing it in a solution of 1 part hydrofluoric acid to 10 parts water for about 10 seconds. Do this outdoors or in a very well-ventilated room. When you cut the titanium, leave a long, thin piece from one corner by which you can hold it and from which it can be wired to the anode.Anodizing was first used to wonderful effect in the early 1970s by such jewelers as Edward De Large and Brian Eburgh. Since then, it has become a popular way of introducing vibrant colors into jewelry because the process is relatively inexpensive and quick to do. However, because the chemicals involved are so dangerous and because it is a fairly technical process, it is possible to send work out to jewelers who specialize in the process to color pieces professionally.

The process of anodizing the refractory metals titanium, niobium, and tantalum produces a range of colors over the surface of the metal that is similar to the colors formed when oil floats on water. The effect is achieved by an electric current being passed through a solution to build up a layer of hard, transparent oxides on the metal. The thickness of the layer of oxides, which determines the colors that are seen, is determined by the relative area, time, and voltage taken in the anodizing process.

The colors that are produced in this way are called diffraction colors, and the process works because each color consists of a specific wave length of light. White light that is, light that carries all the colors penetrates through the oxide layer and is refracted, reflected off the surface of the metal, and then diffracted as it emerges through the oxide layer. In this way, some elements of white light are cancelled out, and some are amplified to produce particularly vibrant shades. The rougher the surface of the metal, the more intense is the color that will be achieved. 

High-voltage colors should be put on first because they do not need to be masked against the lower voltage colors. Apply a "stop out" resist, similar to that used in etching, to areas that need protecting against a higher voltage. It must be completely dry before the metal is immersed in the anodizing bath because "stop out" resists can lift off and peel away at very high voltages. It is possible to apply a coat of resist to a piece, to scratch a design or pattern through it, and to anodize the metal at high voltage. You can then remove the varnish with a suitable solvent or turpentine and re-anodize the metal at a lower voltage. This process produces fine lines across the anodized colors.

Titanium can have patterns etched on it with hydrofluoric acid. Apply "stop-out" varnish to the areas you do not want to be etched before anodizing the piece. Another method is to wrap thin strips of masking tape in a random pattern around a piece of titanium. The anodized effect resembles bamboo stalks.

Backgrounds that blend from one color and merge into another can be created by lifting the piece out of the anodizing bath, which gradually increases the voltage in proportion to the ANODIZING area applied. In this way you can create the effects of sky, sunset, sea, and so on.Tantalum and niobium anodize in the same way as titanium, and if the metals are combined and anodized at the same voltage, different colors will be produced as they produce different colors at different voltages.

Anodized metal can be engraved or abraded and then re-anodized.

Tools and materials

The equipment needed for anodizing is specialized and technical. You will need: a variable transformer, capable of delivering from 3 to 120 volts at 1 amp; a non-glass container for the hydrofluoric acid; a glass vessel to hold a 50 percent solution of lactic acid; a glass vessel to hold a solution of ammonium sulfate made in the proportions of 1 ounce to 1 quart; plastic tweezers; titanium wires for the anode and cathode; strong rubber gloves. Safety goggles should be worn throughout the process.

Writer – Jinks Mcgrath
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