February 7, 2012

Aluminum Anodizing Experiment

To try for aluminum anodizing experiment use sulfuric acid as the electrolyte, Rit brand dye and the boiling water seal method. Picked up a five gallon container of battery acid (sulfuric acid), which is about 50/50 sulfuric acid and water mix from an auto parts store. The Rit brad dye is available from pretty much any grocery store. A 10 gallon Rubbermaid plastic tub was purchased for the anodizing tank as well.


Always wear safety glasses, gloves and an apron or really old clothes. Both the lye and acid used here could be lethal, and may cause serious damage to people and property. Keep a good supply of baking soda solution to neutralize acid spills, and have a large supply of fresh water available if you spill on yourself, you better provide a water spray like shower in your bathroom.

For trial used an extra piece of aluminum tube 6061. The aluminum was washed with soap and water, rinsed, then immersed in a bath of 3 tablespoons lye in one gallon of water. All of the water used in this first batch was distilled water. The caustic bath will etch, or eat into the surface of the aluminum to clean the part. You'll know the surface is perfectly clean when the water sheets over the surface, as opposed to forming drops, or areas of wet and dry spots on the surface. Two or three minutes and this part was etched nicely.

Picked up 5 gallons of sulfuric acid at an auto parts store for the electrolyte. You can use small battery charger to supply electrical. The tank is a 10 gallon Rubbermaid tub. Initially added three gallons of distilled water to the tub, then added one gallon of battery acid. Remember: Always Add Acid to water, don’t add water to Acid it will splashed.

Two aluminum (or lead) plates are used as cathodes and hook up the negative lead of the battery charger. The part to be anodized (anode) is hooked up with aluminum wire to the battery charger positive lead. The part is suspended off the bottom by the wire. Make sure you vent the gas from the process; a good respirator wouldn't hurt either.

Power was turned on and charger set to 2 amps at first. Then increased the setting to 10 amps after a few minutes. Notice the white "fog" or bubbles coming off the cathodes, that indicates current is flowing. The part will emit a few small bubbles too, but most of it is coming from the cathode plates. At the charger 2 amp setting the charger was drawing 2.5 amps, when increased the power to the 10 amp setting, the meter indicated a draw of about 3.5 amps.

While the part was in the acid bath you can mixed up a batch of dye, 4 tablespoons in 1/2 gallon of distilled water. The part was immersed in the dye at room temperature, then the temperature slowly increased to 100 oF. A pot of distilled water was started boiling for the final sealing process. After 15 minutes the part was removed from the dye, rinsed in fresh water, then placed in the boiling water for 30 minutes to seal the surface.

After 30 minutes in the boiling water, the now aluminum anodized part was removed. It seems to have worked very well with a navy blue dye, and it came out very dark.

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