No dye is used. All the color is produced by a variable-thickness
layer of titanium oxide on the titanium plate, approximately the same
thickness as the wavelength of visible light. Light reflects from
both the top and bottom of the oxide, and the interference between the
light from the top and the light from the bottom produces these
colors, in the same way as the thin film of a soap bubble.
Depending on the exact thickness, some colors interfere constructively and look brighter, and others interfere destructively and look dimmer. In the notional illustration to the right, the red colored light is interfering destructively, so almost no net red is reflected; the blue is interfering almost completely constructively, so its intensity is diminshed only a small amount.
The oxide is plated onto the titanium electrically. The titanium is immersed in a tank of water with acid in it to make it conductive. Then a fine titanium wire electrode embedded in a plastic print head is scanned over the surface with precise stepper motors. The movement is computer-controlled, and the voltage is altered depending on the location of the printhead in order to form the desired image. Initial prints were very crude, with hand-cranked positioning and a single button which could print one color, selected by dial. I have been refining the technique and equipment since September 2010, and I started achieving the first attractive results in August 2012.
The resolution is approximately 64 ppi, but I often overprint at 92
ppi for smoother curves. So far all prints have been 2.5 by 2.5
inches, on 3 by 3 inch sheets of 26 gauge titanium.
