Just one. Read this and you can get creative on your own.
http://www.popsci.com/popsci/how20/3f178ca927d05010vgnvcm1000004eecbccdrcrd.html
What it doesn't tell you is this.
First you need: some alligator clips at the local Lowes or Ace Hardware and some speaker wire. Make up 5 of your own little jumper cables with these. You'll need ten alligator clips and a crimper tool or pliers.
Set up 3 new 9 volt batteries on a table. Set them so the postive terminal is on the right side as you look at them. Tape them all down using some duct or electricians tape so they can't move around on you.
Once the batteries are secure and the jumpers are made clip on a alligator clip from one jumper cable to the positive terminal on the number one battery going left to right. Clip the other end of that jumper on the negative terminal of battery number two.
Place a small piece of tape on the alligator clip so it cannot come into contact with the clip beside it on each battery. (the batteries can explode if the clips touch for too long.) Now with the tape in place you can safely place the next jumper cable clip on battery number two's positive terminal and the other end of that one to the negaitve terminal on battery number three.
Now your batteries are hooked up in series.
Take another jumper cable and hook it to battery number one's negative terminal and set it so it is just sitting with the other end safely away from making contact with anything. Place the last jumper cable on the postive terminal of battery number three and set it the same way. You now are ready to work.
Pour a little diet coke, coke, pepsi or whatever you have in a glass bowl. Doesn't take much. Tear of a small corner of a paper towel and soak it in the bowl.
Take the free clip from the jumper on battery number three and clip it to your titanium that you wish to color. Take the paper towel out of the bowl and cover the part you want to anodize with it. Take the jumper from number one batteries negative terminal and move it all over the surface of where the towel sits actually moving it over the towel on top of the towel not under it. Lift it up once you made some progress to check the results. Make note of some areas that need further color and touch them again and move on and continue until the surface you want covered is anodized uniformly. Should come out a nice blue/purple color with three batteries.
Safety equipment should include safety glasses, some latex gloves and some tape to safely keep the ends from touching each other when the batteries are hooked up in series. I don't recommend using more than six batteries. 3 seems to be the best for good deep rich color to me. You can experiment with one, two or up to six but remember 9x6=54 volts. Thats enough to wake you up if you shock yourself so keep that in mind.
STR