Having dyed some scrap metal parts (this blog, 23 April 2012), I moved on to some machined reel parts. On my first attempt, the result was not satisfactory. There were small but obvious flaws, like this spot on the rear end plate.
And this one on the front end plate.
I had taken the usual steps for anodizing: wash in dish detergent, wash with degreaser, handle with finger cots (but just 2 on each hand). My dyeing vessel was a mini crockpot that was not large enough to suspend the end plates vertically. So I attached “legs” made of screws and spacers at 4 lugs . These held the part up off the bottom of the vessel, but oriented horizontally. I now think that attaching the legs was too much handling, and some of the dye smudges are prints from fingers without cots.
So I stripped off the unsatisfactory coating with caustic soda (lye) and made another try. This time I was prepared with some wire hooks so that I did not have to handle the parts, either from wash to anodize or from anodize to dye.
The more complex wire part is a rack that holds an end plate horizontally in the dye.
I also soaked the parts in a hotter detergent solution for a longer time. The caustic soda etch (to remove the first anodize layer) may also have help make a cleaner part.