A very long time ago, I received some scrap rods of titanium. One of titanium's really neat properties (it has several) is that it can be anodized into a rainbow of colors. Unlike aluminum anodizing, where the created aluminum oxide layer is colorless and a dye is needed, titanium anodizes to create what is known as thin film interference. Basically, light waves entering the transparent oxide layer created by anodizing interfere with each other, making new waves and colors. Other metals like niobium and tantalum also have this effect. I thought anodizing titanium looked really fun, so I slapped together an anodizing experiment.
For my anodizing bath, I used 200mL of tap water with 8 grams of Borax dissolved in it. Then, I sanded my titanium and cleaned it with acetone. It is important to not leave fingerprints on the surface.
I looked at
this image to see which voltages anodized titanium to nice colors. Then, I connected the number of 9V batteries necessary to achieve that voltage. Some batteries were at a bit less than 9V, so my first voltage I used was 24V (three batteries). I connected my titanium to the positive on my battery series and clipped a piece of aluminum to the negative. After putting both electrodes in my anodizing bath for half a minute, the titanium had turned a bright blue color!
I wanted to try making a pattern, so I cleaned my blue titanium with acetone again and then cut a tiny square of electrical tape into the letters "Ti." I carefully applied the tape letters to the titanium, being sure not to leave skin oil on the metal. Then, I put the titanium back into the bath, this time using 57V (seven batteries). I wasn't happy with the faint yellow color that voltage made, so I tried again with 73V (nine batteries). That gave a nice pink color, so I took the titanium out and removed the tape. The pattern had worked, and I now had beautiful blue letters on a pink background. The experiment only took half an hour, but it had great results!
For my anodizing bath, I used 200mL of tap water with 8 grams of Borax dissolved in it. Then, I sanded my titanium and cleaned it with acetone. It is important to not leave fingerprints on the surface.