Magic Color on Metal: Titanium
As you may know, most of my most personal and ambitious work includes detailed imagery in anodized titanium, a truly marvelous and magical material. Here is an article I wrote that gives some basic information on how that work can happen. It is a bit on the dry side in terms of prose, but if you want the info, this is a good start. Not as comprehensive as taking a class or workshop with me, of course, but it is more than I had to get me started originally, so go ahead– give it a try!
By Noël Yovovich
Copyright 2007 Do not copy, publish or distribute without permission
The technical details of why titanium turns colors
Fortunately, it is not necessary to have any understanding of the process by which color appears on the surface of titanium, in order to take advantage of the fact that it does. Nonetheless, here is a very basic explanation of the remarkable, even magical, way that this amazing material turns colors.
Titanium is one of the so-called reactive metals. This means that it reacts to certain conditions—current or heat, in this case—by developing an oxide layer that appears brightly colored, even though there is no pigment whatsoever. The color is, in a sense, an illusion. The layer varies in thickness according to the degree of heat or the amount of voltage. This oxide layer is quite chemically inert and quite permanent. It is also very thin and transparent. Its transparency allows light to bounce off of both the front and back of the oxide layer. Because the layer corresponds in thickness to wavelengths of light, the bounced light reinforces certain wavelengths (colors) and interferes with others. This causes the oxide layer to appear colored.
The mechanism is the same as for the colors on an oil slick or a soap bubble, but with two important differences. First, it is permanent. Second, the thickness of the layer changes in increments, causing it to produce some colors, and only those colors. So titanium will not turn red, for example, but will produce a strong pink under the right conditions.
Titanium is not the only metal that performs this neat trick. Niobium and tantalum do, too. Niobium is fairly widely used in jewelry, and actually is easier to color, to form, and to polish. It is much less stiff and hard than titanium, and, unlike titanium, will readily take a high shine. The colors it produces are much more bright and vivid.
If all this makes niobium seem like a better choice, the techniques outlined below will work just fine with that metal as well, with some exceptions. Niobium must be anodized, which is to say, colored with electrical current—it does not color in response to heat. And, as metals go, it is “gummy”, which means that it does not offer the same opportunities for contrasts of texture as well as color, as described below, that titanium does. And the colors are so bright as to possibly be considered garish. Lastly, it is more expensive than titanium, at about five times the cost, though neither is very costly. If you experiment with niobium, you will find that if you bend or form it after coloring, the color will change as the surface is stretched or compressed. Titanium doesn’t seem as prone to this, but, in any case, it is too stiff to be formed much, even when thin.
Titanium and niobium each have unique qualities to offer the metalsmith. The rest of this discussion will deal solely with titanium.
A few more technical details
Because titanium reacts to heat by oxidizing, it cannot be soldered, welded, or annealed in an oxygen atmosphere. This means that for the purposes of the studio metalsmith, those things cannot be done at all. As a result, it must be cold-joined. This means it can be wire-wrapped, drilled and hung, riveted, set like a stone, or made wearable by whatever other method your imagination can provide.
What colors can I get?
As either temperature or voltage is increased, the succession of colors on titanium will always be the same. The exact voltage, or time with the torch, will depend on the size and thickness of the piece of titanium. The correspondence between voltage and color, at least in studio conditions, is somewhat approximate. Some colors (such as blue) will appear over a fairly wide range of voltage or heat. Others, such as green, are more fleeting or difficult to control. The colors, in order from lowest temperature or voltage to highest, are: gold, brown, purple, dark blue, light blue, yellow, pink, magenta, royal blue, blue-green, yellow-green. There is a narrow point between light blue and yellow that shows a very pale green, almost white. And between yellow and pink, it may be possible to stop at orange.
It is assumed, for the purposes of these instructions, that the reader understands the use of electricity and will observe all necessary precautions to avoid shock.
An anodizer consists of a power source that can provide variable DC (direct current) voltage up to at least 80v at low, constant amperage, generally between 1 and 3 amps. The negative lead is attached to a strip of conductive material, usually stainless steel (the cathode) which is suspended in a conductive bath. Water, by itself, is not conductive enough, so it is made more conductive by the addition of trisodium phosphate (tsp) or a phosphate-free substitute (sold at hardware stores for cleaning or removing wallpaper).
The positive lead is attached to the titanium work piece, also suspended in the bath, which makes it the anode. The voltage is set and the power turned on until the desired color is reached, then the power is shut off and the titanium removed and rinsed thoroughly. You cannot be sure what the color really is until the piece is rinsed and dried.
It is vital that the anode and cathode do not touch when the current is on, and that you do not put your hand in the solution when the power is on. Wear rubber-soled shoes, and take care to avoid shocks. As long as you do not stick your finger in the bath during anodization, the process is quite safe. Rubber gloves are a good precaution as well.
When first using an anodizer, it is best to begin by creating a test strip. A long piece of titanium, say, 6” x ½”, can be marked off for every five volts (a steel ball bur in a rotary tool works well for this). Then the entire strip is anodized to 5v. The first segment is then lifted out of the bath, the voltage turned up to 10, and so on.
The exact results will vary according to the amperage of the anodizer (higher-voltage colors will be easier to get if amperage is very low, though the color will develop slowly) and the condition of the surface of the titanium. It is not possible to go into every detail of the variations here. This is why experimentation is a must. The best readily available source of information about reactive metals (as well as the metals themselves, and tools and supplies for this process) is Reactive Metals Studio, Inc. They can be found on line at www.reactivemetals.com, and by phone at 928 634-3434.
Because of the variability of the process, it is best, when anodizing pieces which must match, such as earrings, to color them at the same time.
Multiple colors can be used on the same piece by either masking areas and removing the mask bit by bit as you work your way from higher to lower voltage, or by grinding the oxide off of areas to provide a fresh surface to color. The first method creates a contrast of color without creating texture. The second gives a contrast of both color and texture.
Any material that will keep an area dry will work as a mask. This includes tape, rubber cement, fingernail polish, paint pen, etc.
Likewise, any tool that will remove the thin oxide layer can be used to expose a fresh surface while creating texture. Sandblasting and grinding with steel burs, especially ball burs, work well, as does grinding with a steel brush, for large areas.
A word to the wise: if you get an area that you are happy with, cover it with tape, nail polish, etc, because higher-voltage colors may still “advance” to the next-higher-voltage color when you anodize again, even if you are using a much lower voltage.
When heat-coloring, you must depend on practice and luck to make pieces match, but heat-coloring is, by its nature, a less precise undertaking. This is part of its charm. Whereas anodizing creates areas of one solid color, heating tends to create gradients and rainbow-like effects. Though it is not possible to mask areas from the heat, areas can be ground down to offer a fresh surface. However, if those areas are heated, the previously-colored areas will also be heated, and will change color as well.
It is important to work on a very clean surface, such as a brand-new soldering pad or firebrick. The titanium should be absolutely clean and dry—any trace of moisture or finger oil will affect color and show up as a blemish.
Play a bushy flame over the surface from a couple of inches away to get even color. Be patient, and let the color develop slowly. Bring a hotter flame in close for a change of color in one area. The only way to understand and become comfortable with this process is to try it. If you keep notes about your experiments, it may be easier to duplicate results you like.
The information here is far from exhaustive, and is intended to guide you through the first steps of getting acquainted with this amazing material/process. Titanium is unlike any other material—light, strong, and capable of feats of magic!