March 20, 2008
The short answer is: “No.”
In detail, the colors are caused by a particular trick of physics: Optical Interference. As is described in detail on this page, the colors are limited by the behavior of photons. There is no dye or coloring agent to give us precise control.
Red, in particular, cannot be produced because it’s wavelength is twice as long as blue. So if the interference allows red, it also allows the shorter blue through. This creates the secondary color called Magenta, red-violet, or purple.
March 18, 2008
Here’s another question I frequently get:
I followed your instructions on building an anodizer
and I would like to say that you have made a great job illustrating it. My anodizer is the dimmer and light bulb type it delivers a maximum of 160 Volts.I prepared a solution of TSP in distilled water placed the cathode (aluminum foil) and the Ti at the anode ran the circuit. The voltage keeps rising slowly and I get shades instead of definite colors (mostly violet, golden and pale blue). I can’t hold the voltage at a definite value. What should I do to get smooth colors? I tried adjusting the voltage first then immersing the piece but the voltage after immersing is lower than what I’ve just set it to. Please help me out here and thanks in advance.
First of all, the dimmer based voltage control is going to be a bit temperamental and unstable. But I used one myself for years before replacing the dimmer with a Variac.
Aluminum should work for a cathode, but should be lightly sanded to remove the invisible insulating oxide layer that spontaneously forms. I usually use titanium, but have been told by many that stainless steel works well.
When you have a large capacitor smoothing a the choppy dimmer voltage, the top end will be a bit mushy. The lower voltages are the worst for this effect. The tan, violet and blues are at the low end of the voltage scale.
Another issue in getting smooth colors is getting the voltage everywhere simultaneously. You should have the piece to be anodized immersed in the solution before completing the circuit to the leads. That is, you need a switch to turn the leads on and off, while the anodizer is running at the voltage you want.
Cleaning and chemically etching the metal before anodizing also helps assure a uniform color, and is generally considered necessary for getting the higher voltage colors.
The voltage measured on the leads or capacitor will drop when you start anodizing, and should rise back to your preset voltage in a minute or so. The time depends on how big a piece you are anodizing, how big your cathode is, and on the efficiency of your electrolyte.
Another possible problem might be the material of your attachment to the anode piece. Only titanium or niobium should touch the electrolyte at the positive side. Never use copper wire or regular (galvanized or tinned) alligator clips to immerse your piece. The current will just go though that, and little will be applied to your piece.
March 18, 2008
Here is a typical question that I get asked:
I would like your advice: Besides the plastic container, what else do I need to anodize titanium grade 23 or grade 5. I called Reactive Metals to buy the machine for $206 , they told me to buy a mesh but I do not know what or where to buy it. I am a little scared of getting hurt if I do not know how it really works.
Any help will be really appreciated.
The question seems to be, what is needed to get started. Peter has already bought an anodizer, a 0-150vdc voltage supply.
The “mesh” might be one of three things.
- A large-area cathode (negative pole immersed contact) could be a mesh of titanium or even stainless steel. I use a coil of wire for this, but a plate of metal does fine. Ideally, you want to have a non-conductive porous material ( maybe a plastic mesh) between the cathode and the work piece, in case of contact. Rubber non-skid shelf liner mesh/screen is cheap and good for this.
- A mesh basket made of niobium wire makes a good anode connection for loose parts. A titanium wire basket will work, too. Just not quite as reliable at higher voltages.
Note: I haven’t tried this myself. I use a homemade titanium clip and the niobium clips that ReactiveMetals sells.
- A plastic mesh basket such as a salvaged automotive windshield washer fluid filter can also be used on the anode side by running a niobium or titanium wire into the basket full of little parts.
Note: I haven’t tried this myself, but have heard of it being used by others.
One can easily weave your own basket from titanium or niobium wire.
One important final note: If you are afraid of getting hurt, please do some more reading about electricity and safety precautions. Wear rubber gloves, and always double check where all the live contacts are when you are working. Read my old anodizing page over until you understand everything in it. It may not be complete, so do ask questions to help me fill it out.
March 16, 2008
Titanium is colored by applying oxygen to the metal surface, usually through a process called anodizing. There is a pretty good description of how to anodize titanium on MrTitanium’s website. There is also a page that tries to explain how oxygen makes it colorful. If there are questions or suggestions after reading those, I’d like to see them. Feedback given here may modify those pages.
Don’t confuse anodizing titanium with anodizing aluminum. The electro-chemistry is similar, but the procedure, electrolyte, voltage needed, current consumed, the time it takes, and safety hazards are different. You can anodize aluminum with a titanium anodizer, but not the other way around.
Safety issues with titanium are mostly high voltage related. The electrolytes recommended are generally safe enough to use on your garden for fertilizer or pest control: Ammonium phosphate is lawn fertilizer, and TSP is a cheap detergent that can be used to control plant parasites, and washes down to enhance root growth.