EDITED TO PROVIDE MORE DETAIL –
Just a note, I make chainmaille jewelry and it is easy to make an anodizer for titanium/niobium (lots of videos about it on youtube, Dylan Kowalski even has some). I currently use multiple 9V batteries in series to generate the voltage I need and use a stainless steel spatula as my cathode, although I might need a larger cathode if I were to do a yoyo. I also would like to invest in a volt adjustable power source as some point, BUT IT IS NOT NECESSARY. This website also has some good info on anodizing: http://mrtitanium.com/anodizing.html
I haven’t anodized a Ti yoyo yet because I haven’t been able to afford one but hopefully some day I will get one and then I can make it a sweet purple (like pictured - Niobium tends to anodize more richly than titanium, but you can etch titanium to get deep colours). The thing that really excites me is that you can easily touch up the colour if it starts to wear (which with titanium means it will start migrating to a colour lower on the scale and typically not reach down to raw). This is because as opposed to anodizing aluminium (which creates a clear oxide layer that acts as a primer for coloured dyes), anodizing titanium does not use dyes, instead it create a crystalline oxide layer that changes light refraction as it gets thicker (and the thickness is regulated by voltage); this creates a whole spectrum of iridescent colours. So even if you scratch the finish, you can pop it back in the bath at the same voltage and it will “heal” the finish back to a uniform layer (its magic!). (Ps: A scale for voltage and colours with Nb/Ti attached.)
So moral of the story is that I would encourage people to get into anodizing titanium themselves. It is way more accessible that aluminum and it can be super fun. Plus if you screw up, you can use an etcher (which is caustic) to start over.
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