I've dabbled with a little Ti anodising for a while, but having completed a frame I fancied some wild graphics and wild colours (yes I know: like a four year old who has just been given a paint box). I rapidly discovered it's a minefield and not many folk are at all keen to tell you how they do it. That's a little unusual in the frame building world as most folk are happy to share knowledge.
Anyhow, it's been a bit of a rabbit hole and I'm no expert but I'm happy to share what I've learnt so far. A WARNING though: some of the chemicals and techniques are dangerous, so do your own reading as well, take care and don't blame me if it goes awry.
Right, here goes, Ti anodises happily and the colours obtained are voltage dependant, it can be done with stacked batteries but to get the vibrant greens, purples and so on a variable voltage supply seems a necessity. Available via EBay for peanuts 0-110 volts.
Preparing the titanium: the colours and intensity of colour it seems can vary quite a lot depending on the grade and surface finish of the Ti, polished, brushed or media blasted, so experiment and take your pick.
The titanium has to be clean of grease and contaminants, I've wiped down with acetone, then alcohol, then distilled water.
The next and probably for me most hard to solve and nasty part of the job, is to etch the titanium, don't ask me why, or what it's actually doing to the surface but it appears to be necessary for a good finish and vibrancy of colour. The etchant of choice appears to be hydrofluoric acid, this is absolutely awful toxic, poisonous, dangerous and environmentally unfriendly with bells on stuff - that said in the USA, but not the UK, it's available as or as part of "Whink" rust stain removal fluid. Goodness knows why the UK is currently desperate to adopt US standards (I have an opinion, you might not like it). Several people on the good old internet claim to have come up with some other etchant that works beautifully, is safer and is a great option for those in the UK - then they refuse to tell anybody what it is. It's probably a bottle of "Whink" they got in the UK via EBay, which is what I did. I read about hydrofluoric acid and triple gloved. I'll be getting some super duper chemical gloves next as I'm terrified of this stuff, and I used a mask and face shield. To think you can just buy this in a shop over the pond, amazing, utterly weird, I've got it stored in a locked metal box.
Now the fun bit, the anodising. It's not really possible to stick a frame in a vat of electrolyte so brush anodising is the preferred technique, your "brush" or foam/cotton wool clipped to the negative becomes electrolyte as it's soaked in it, the frame is clipped to positive.
There's much discussion about preferred electrolyte, it seems that Borax gives quicker anodising and possibly better colours than sulphuric acid, and it's easier to work with and obtain.
I have anodised using vinyl stencil masks but at higher voltages the heat makes bleeding under the glued edges more likely. Anodising an area, then masking and media blasting gave me better results for graphics and logos.
The masking is a learning process too, after some experimentation and exasperation I'm using Aslan branded vinyl suitable for medium duty blasting, the main issue I was having was not wearing through the vinyl but keeping the mask stuck on, particularly smaller bits like the dots on the "i"s. I think I've cracked that problem by leaving the application tape on, giving the mask a light blast which hammers it down, then removing the app tape. I suspect that with this approach I might have been able to use any decent weight of vinyl for blasting with glass bead medium.
If you want to mess about relatively safely to start with you can forget the etchant, and the electrolyte and just use a few batteries and some water, I achieved some nice blues, purples and brown colours with that approach.
There you go that's the sum total of my knowledge to date, I hope it helps someone, and if you know what I can substitute to etch the Ti without using mega horrible chemicals do tell me. Apart from the etchant it's simpler than anodising aluminium, that is a whole different kettle of parsnips, been there got the tee shirt.
April 2021 addendum to this post: After some more "research" (Googling!) I've found that a better etchant is "Multi-etch ™ ". Trouble is it's unobtainable in the UK. It appears that a 0.5m solution of a couple of chemicals works very well though:
Ammonium persulphate and sodium fluoride 114g and 21g in 1 litre distilled water, follow the instructions for proper Multi-etch ™ . Use it warm or make a 1M solution, or both.