While I was in graduate school at San Diego State University I became interested in the anodizing process. I had been working with aluminum in jewelry for a while when Arline Fisch brought back some basic anodizing aluminum information from Bezalel Academy in Jerusalem. I put together a primitive anodizing set-up, which eventually lead to my doing my M.A. thesis in 1981 on the anodizing aluminum process and its applications for jewelry.
I moved to New York City that fall and was offered a teaching position at Parsons/New School. There I met technical consultant Thomas Pignatelli, who helped us put together anodizing equipment. Through him I learned more about the process and became acquainted with the Sandoz Company and their dyes and chemicals, which I now use. The set-up in my studio is based exactly on what is found in industrial situations. This has made the process more efficient and the outcome more predictable.
I believe anodized aluminum is an ideal material for jewelry. Aluminum is light in weight, and it can be colored in a wide range of hues through the use of the anodizing process. I find stimulation in the irony of using an industrial material and process for jewelry and combining this with more traditional material, such as gold, silver and stones.
Anodizing is an industrial process that produces a stable oxide film on the surface of aluminum. The work piece is attached to an aluminum hook or wire and then immersed in an acid bath (electrolyte solution), it receives the positive (anodic) current, and as oxygen is released an oxide film containing billions of pores similar to that of a honeycomb structure is produced on the metal surface. These pores will then accept dye. Once sealed, the metal is strengthened and protected from corrosion and is resistant to water, oil, salt, weather and general wear.
For bright, clear colors on relatively pure aluminum the sulfuric acid process is used. A chromic acid process, which produces a less clear, thinner coating and color, is used for less pure aluminum alloys. (See also Jewelry Concepts and Technology by Oppi Untracht, New York: Doubleday, 1982 for more information on the chromic acid process.)
Anodized aluminum has a variety of industrial uses in architecture and building materials, hardware and housewares. Its applications for jewelry are exciting. In addition to the durability of the anodized surface, aluminum is light in weight and the color palette is almost endless. The Sandoz dyes are rated highly in color-fastness and will not fade noticeably for many years. By controlling the variables of time and temperature in the acid bath and the time and temperature of the dyes, multiples of the same color can be easily produced.
The process is a bit more time consuming than that of coloring refractory metals, such as titanium and niobium, but it produces on the aluminum a clear field of color that is much more durable. The color can be solid or shaded through overdyeing. Resists can be used to produce more than one distinct color on a surface, and the dye can also be painted on.
Fumes are created while using the caustic etch and the anodizing bath and the work area must be well-ventilated. (For more information on ventilation, consult Ventilation: A Practical Guide, $7.50, available from The Center for Occupational Hazards, 5 Beekman Street, New York, NY 10038.) As with any electrical set-up, normal precautions should be taken. Never touch the anode (work piece) and cathode (lead) or connecting rods or wires while the rectifier is on. The current generated could be extremely dangerous. Rubber gloves should be worn as insulation against electric shock and also for protection from the acids and lye.
|Fasten aluminum wire or hooks to piece and to copper rod (see Diagram A). Tight fit is very important, Do not touch the piece with bare hands until after it has been sealed. The surface is extremely porous and vulnerable to dirt, grease, fingerprints after anodizing and before sealing. Hooks must be etched or filed after they have gone through the anodizing cycle before they can be reused.|
|Prepare bath with Sulfuric Acid, 15-18% solution in water. Ideal temperature 70°F. Bath will heat up as current is generated and cooling may be necessary. (See cooling system on Diagram A.)|
|Set voltage meter at about 12 volts. Current selected will depend on the amount of metal (surface area) in the bath. A current density of 10-25 amps/ft2 is recommended. Immerse piece in bath for 15-60 minutes, depending on desired results. Longer immersion time results in more intense color. For most colors 30 minutes will be sufficient, although black may need the full 60 minutes.|
|Rinse in clean water.|
|Neutralize in Baking Soda and water, 1oz/gallon.|
|Rinse in clean water.|
For more than one solid color on a piece of metal, resists may be used. (I use a vinyl synthetic resist, which can be easily peeled off). A resist is applied to a very clean surface before starting the process. For every additional color the piece must go through the process one complete time. To retain the original color resist must be applied to previously dyed surfaces before you begin to dye another part of the piece.
A shaded effect can be achieved by immersing the piece partway into one dye and then immersing the other part in another color, the area where they meet will blend together, similar to watercolor. Dyes may be mixed in the containers, or pieces may be overdyed by immersing in one color, rinsing, then immersing in another color.
Dye may be painted on the surface. The dye should be simmering. The color will be more pale than if it was immersed.
Permanent type felt pens may also be used after anodizing and before immersing in the dye. The piece must be carefully dried before the pen is applied. They act as a resist for the water-based dye while imparting the color of the pen. (Pen colors may not last as long as standard dye colors, but they serve the same purpose.)
Most of the equipment is available through chemical supply companies, hardware stores and electrical equipment companies. Much of it can be obtained through surplus outlets. Buckets may also be obtained from plastics supply companies.
Dyes can be obtained through Met-L-Art in Wilmington, DE, (302) 475-1906. They sell small quantities—2 oz. packages. Additional dye information may be obtained through Sandoz Technical Service Department, (704) 372-0210, 4000 Monroe Rd., Charlotte, NC 28205.
Rectifier: available from I. Shor, Gesswein, Allcraft and all big metalsmithing suppliers. Estimated costs: $150-$200, excluding power supply, which is available for $100-$800.
David Tisdale’s work was featured in a solo exhibit at Helen Drutt Gallery, Philadelphia, December 1984—January 1985.
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