Anodizing procedures


Note:

Anodizing most closely resembles standard electroplating. When a reactive metal is suspended in a electrolytic bath as an anode(+) and current is passed through the bath, oxygen is produced at the anode surface. This oxygen reacts with the metal to form a thin oxide film that generates colors. The transparent oxide increases in thickness in relation to the amount of voltage applied. At any given voltage the oxide will grow to a specific thickness (i.e. color) and stop, having reached a stage where current will no longer pass. This phenomenon of voltage controlled growth means that the color is also voltage controlled.

An area of oxide produced with a high voltage will not pass current from a lower voltage. In other words an area anodized at 60 volts will not need masking when an adjacent area is anodized to 40 volts. It follows that multiple anodizing processes should proceed in decreasing voltages. Working in descending order will save masking and generate fewer errors.

While oxygen is generated at the anode(+), hydrogen is formed at the cathode(-). Titanium and stainless steel make most convenient cathodes. This process does not have much throwing power and it is necessary to have a cathode equal to or larger than the anode.

The electrolytic solution can be almost any liquid capable of carrying current. Such diverse solutions as Coca-Cola, Sparex, sulfuric acid, ammonium sulfate (fertilizer), magnesium sulfate (Epsom salts), trisodium phosphate, dish detergents and even wine will work. Recommended here is a solution of 3 to 10% by weight trisodium phosphate (T.S.P.) in solution with distilled water. The percentage of chemicals in the solution will determine to some extent the length of time for the desired reaction to be completed. Slowing the reaction can be achieved by lowering the concentration of chemical in solution.

Anodizing set up

Power supplies

The power supply required for anodizing has a much greater range of voltage control and lower range of current capabilities than plating rectifiers. The requirements are 0-150 volts DC variable in one volt increments and from 2-5 amps. Larger capacity power supplies may be necessary for work larger than jewelry and in high volume production.

Anodizing procedures

Bath anodizing

Bath anodizing

This technique is best for one color, rainbow and mass produced work. You will need, 1) a power supply 2) a plastic or glass container 3) electrolyte 4) a cathode and 5) titanium clips, holders or hooks to hold the work. With the pieces to be anodized in the bath, turn the anodizer ON and slowly increase the voltage. You may see small bubbles appear on the surface of the anode. This is an indication that the anodizing is taking place. The colors will continue to change as the voltage increases. If you do not like the color, increase the voltage and produce a new color. You can never bring the color back down once it is passed. Turn the power OFF, remove the piece, rinse and wipe dry. Only then will you see the true color.

 

Anodic painting

Sponge ToolNote: The metal ferrule of paint brushes, other metals and conductive materials that could come in contact with the operator or cause a short circuit should be covered with electrical tape or coated with a plastic coating. Always wear rubber gloves. This is where the real graphic potential of this process comes into play. This technique brings the electrolyte to the work. Applicators can be made by soldering an insulated wire on to the metal ferrule of an artist's brush or clipping on to a sponge with the cathode lead wire.

Pen Tool
Connect the anode(+) lead from the power supply to a reactive metal workpiece. Connect your applicator to the cathode(-) output of the power supply. Moisten the applicator in electrolyte. Turn on the power supply and set the voltage to the desired level. Touch the applicator to the surface and the colors will begin to appear.

If the applicator is held in one position the colors will slowly radiate out from the point of contact. With excess electrolyte and constant movement, even large areas can be evenly colored. Fine detail work can be produced with an almost dry brush.

Masking

Defined areas of color can be achieved with the techniques described above and suitable maskings. Masking agents like asphaltum, lacquer, photo resists and specialty tapes can be applied by a variety of techniques. Multiple anodizing steps are performed as layers of resists are removed for spectacular effects.

 


Disclaimer of Liability

About the author: Bill Seeley is president and founder of Reactive Metals Studio, Inc. He is considered an expert in this field with over fourteen years experience as artist, teacher and consultant. This excerpt was compiled from "Studio Preparation and Coloring of Titanium" Bill's Masters Thesis completed at the University of Kansas. If you have questions please feel free to call 800/876-3434 or FAX 520/634-6734.


Copyright 1994, 1995 ArtMetal

Author: Bill Seeley
ArtMetal Editor/Curator: Enrique Vega

Last Updated:Thu, May 1, 1997