Guide to Coloring Reactive Metals

by Bill Seeley
"Processes, methods, and apparatus presented herein have not been tested or verified by ArtMetal in any way. Anyone using any of this information is doing so at their own risk."

During the past ten years there has been a steady growth in the use of the reactive metals in jewelry and art. Within this group of metallic elements the most common are titanium and niobium. Titanium remains the most popular for commercial jewelry, followed by an expanding use of niobium. Niobium is both more ductile and more colorful. These metals can be cut, formed and finished with standard hand and power equipment. The high colorations can then be achieved through a simple anodizing process.

Note: In the following discussion of the techniques and processes for preparing and coloring these metals, titanium will be used as the reference metal with notes to any variation as they apply to niobium.

Interference colors

The colors produced by these metals are known as interference colors. There are no pigments or dies involved. They are generated by a transparent oxide film grown on the metal surface. The colors develop when part of the light striking the surface reflects and part pass through the film to reflect off the metal below. When the delayed light reappears and combines with the surface light waves they may either reinforce or cancel. This generates a specific color. The thickness of the oxide film dictates the color. In nature these colors can be found in the eddies of an oily wet street and in the iridescent colors of some insects.

Surface preparation and forming

All forming and surface finishing must be done before coloring. Most surface finishing techniques can be adapted to these metals. Die cutting, bending, stamping and surface textures can be achieved with standard tools. Work can be vibrated, tumbled, sanded and polished. Finishing will be more time consuming than with traditional metals. Consideration should be given to sanded and textured surfaces. Light gathering scratches and marks will add flash and variety to the work. Textured surfaces also add some protection against abrasion.

Chemical etching

Titanium requires a chemical etch to prepare the surface for high voltage anodizing. Multi-Etch is available in our current catalog and provides an excellent alternative to hazardous acid solutions. The basic commercial etching solution is: 3% Hydrofluoric acid plus 30% Nitric acid in water. No acid finishing is required by niobium.

Note: All chemicals should be used under strictly controlled conditions. Hydrofluoric is an insidious acid and requires special handling equipment, safety precautions and disposal.

Forming

Tools of hardwood, nylon and steel can be used to dap, bend, chase, texture and form Grade #1 annealed titanium and niobium. Niobium will easily die form and may be chased or repousse'd. Surface textures can be cut with a flex shaft, sandblasted and engraved. Roll printing is most effective with niobium. (Protect the rolls with copper or brass when roll printing titanium.)

Both metals require lubrication when drilling and machining. The low thermal conductivity of titanium can cause heat to build and damage cutting tools. Use cutting oil or soapy water as a lubricant to lengthen tool life.

Coloring

Coloring can be achieved in two ways; thermal oxidation and electrolytic oxidation (anodizing). Both processes do essentially the same thing. Through electron excitation, the metals react with oxygen to form a thin transparent film. Thermal oxidation (heat coloring) is simple, but difficult to control. Anodizing is infinitely more predictable and is the only effective way to color niobium.

The colors produced appear in up to five repeating orders. Most of the current jewelry is produced with the first two orders. All the colors of the light spectrum are not produced. True red and forest green are not generated.

When the oxide is of a thickness to generate interference colors, its depth is measured in angstroms (Å=1/100,000,000 centimeter). This layer can vary in thickness from 500 to 1,000Å+ depending on the color. It is not the oxide itself that is perceived by the viewer but its effect on light.

Although harder than the parent metal, the extreme thinness of this oxide dictates that it is not a strong wearing surface. Bracelets, belt buckles, rings and items that normally receive heavy abrasion should not be considered unless the metals are protected by other design elements.

Thermal oxidation

This is the type of coloration that most metalsmiths start with on titanium because no special equipment is necessary. At temperatures as low as 640 degrees F titanium will begin exhibit its first golden colors. Then, with increasing temperature and time, a variety of hues will appear. A torch or small kiln can be used.

Throughout the thermal coloring process cleanliness is an absolute necessity! Dirt, dust, oil and finger prints will discolor the oxide as it is growing. It is possible to contaminate the surface for special effects. Refinishing a piece that has discolored during the heating operation is difficult and time consuming. Niobium does not heat color. When heated to a dull red and held for 10-15 seconds it will produce a tough gray/black oxide. This is a very hard finish and works well in many applications where a black metal is desirable. The piece must be formed first because heating hardens the metal. The black oxide can be polished, waxed and even engraved and anodized.

Flame coloring

Here a torch becomes the artist's brush. A free painterly approach to the work is necessary as precise effects and color control are difficult. Softly shaded washes of color and some rainbow effects can be generated with a little practice. Almost any torch will do, as the temperatures required are not high. Large soft flames will produce areas of even color. A small hot flame will generate rainbows of color radiating out from a point.

Kiln coloring can be done in a standard enameling kiln. Running at temperatures between 800 and 1,200 degree F, a few minutes in the kiln will produce golds, purples and blues. Actual temperatures and times will relate to the size and thickness of the metal. Solid one color pieces can be produced with this method.


Disclaimer of Liability

Reactive Metals Studio, Inc., ArtMetal, and the author assume no responsibility and disclaim all liability for injuries and /or damages and/or loss of profit from the use or attempted use of the processes described in the following paper.

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.


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Copyright 1994, 1995 ArtMetal

Author: Bill Seeley
ArtMetal Editor/Curator: Enrique Vega

Last Updated:Sun, Jan 21, 1996