What is anodizing?
Anodization is “an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts. The process is called anodizing because the part to be treated forms the anode electrode of an electrolytic cell. Anodizing increases resistance to corrosion and wear and… can also be used for a number of cosmetic effects.” (Wikipedia)
In a nutshell jewelry (rings, pendants), knife handle scales and hardware (screws, pocket clip, backspacer, etc.) are frequently anodized to create a dynamic color contrast.
Can all metals be anodized?
Most metals can react with oxygen to form an oxide layer at the surface of the material. In some instances, this can happen spontaneously, while others require the addition of heat to get the reaction started.
There are many metals that can be anodized including Magnesium, Zinc, Niobium, Tantalum, Aluminium, and Titanium. From the knifemakers and jewelers’ side, it is generally Titanium that is anodized.
Titanium is extremely prone to oxidation and a micro-layer of oxide will form within moments of exposure to the atmosphere. While this may seem at odds with the titanium’s inert nature, it is actually this oxide layer (titanium dioxide) that protects the metal from further corrosion.
The size of the charge, and its duration, determines how much oxidation takes place, and therefore, the amount of oxide that develops on the surface of the metal.
Fun fact: beyond just looking cool as all get-out, anodization increases material surface hardening for greater resistance against scratches and scrapes.
Titanium dioxide layers are thin and measured in nanometers (i.e. one-millionth of a millimetre), and it is this thinness that is the key to the process of adding colour to the material, as anodised titanium works by selectively filtering specific wavelengths of light through a process called refraction.
Depending on the thickness of the titanium oxide layer, certain wavelengths are enhanced, while others are cancelled out. Thus, anodised titanium gains its vibrance not by the addition of colour, but by the selective elimination of it.
We will look at two different process of anodizing titanium with a few inexpensive tools you can even do your own anodization at home in your garage.
Electric Current Anodizing
For more consistent and even results, opt for anodizing via an electrolytic process. This is great for mono grades of titanium (ie: non-patern-welded ) such as your liners, pocket clips and screws.
- Anodizing DC power supply (9V batteries can be used)
- Non-reactive containers (3 minimum)
- Simple Green or another degreaser
- Borax (as electrolyte)
- Scrap metal as an electrode
- Paper Towels
A clean work area is the place to start. Clean the titanium part that you wish to anodize. Clean with the degreaser. Rinse the parts of while wearing gloves as the idea is to not get any oils onto these parts as this will give you blotchy/uneven results.
Prepare a borax electrolyte solution in a glass or plastic container. Connect the negative electrodes to a piece of non-rusting metal and place this in the solution. A spare piece of Titanium or aluminium works. Suspend the parts to be anodized in the solution from a non-reactive wire, titanium wire is a good option.
Be careful that the negative and positive anodes not to touch each other.
Playing with the voltage will give different colours. You cannot anodize back down to a previous colour (lower voltage) without removing the anodizing first, so have a colour in mind and before you start, or use a test piece.
Remove the parts when the desired colour is reached. Rinse off the electrolyte solution.
To achieve multiple colors on one piece or create intricate overlays, you can simply mask off the piece and anodize the highest voltage setting first, continuing to unmask the areas in order from highest to lowest voltage.
Clean the piece between processes. Continue until you have obtained all of the hues you want on the piece.
Heat / Torch Colouring Titanium
This process is probably the best for pattern-welded titanium or titanium damascus like our DSC Titan or DSC Zitan ranges. This is because of the mixture of different grades of titanium (typically grade 2 & 5) in the alloy that form oxides at different rates. Plus, with enough practice, you can create colour gradients.
Heat anodization works by artificially coaxing the natural oxides that grow on titanium over time at different temperatures to bond more readily with the oxygen in the air.
- Take the titanium to the finished stage, normally 1000 grit or higher.
- Buff to your final desired finish (a higher-finish results in brighter colours)
- Wash with alcohol while wearing gloves
- Wash with sunlight soap, still while wearing gloves.
- Still wearing gloves dry with a lint-free cloth.
- Hang up and slowly heat with a gas torch (gas stovetop).
- Make sure that it is an even distribution of heat over the article and that you slowly increase the heat. It’s important to remove the heat every few seconds so as not to overheat/overshoot the desired finish. P.S the colours can change very quickly.
- If you have overshot the desired colour point, simply buff using the white compound and then to continue from point 3 again.