I can see by your post that you did your homework, anodizing is like everything else in Life, you get out of it what you put into it.
I agree with your proposition that you anodized too long. Don't underestimate the evil effects of excessive dissolution. But ironically; if you stopped dissolution entirely, you wouldn't form a suitable anodic layer at all.
I've heard this "900 Amps/min./sq.ft."stuff before. I have verified that the "720 Rule" is quite accurate since I can measure anodize thickness. That means replace "900" with "720". The 720 Rule is based on real electrochemistry (it has a provable mathematical base) the 900 stuff is from some amateur's website and has no basis at all beyond his particular setup. If your setup isn't identical to his (fat chance) it isn't likely to work. His connection method is poor, and he doesn't use CC, the 900 stuff is a fudge factor to compensate for this.
You are correct in saying that you actually anodized at 15.6 A/sq.ft.. If you were using LCD electrolyte, the pores would have been smaller, not larger, not so small to make dyeing too difficult, just harder than it should be. This leaves excessive dissolution, and its characteristic of opening up the pores to too large a size. The 110 deg. dyeing is an error in the documentation, Caswell is been slow in correcting errors, but I expect that to change.
On what basis do you rule out #5? Threading is no guarantee of a good connection, its mechanical and is prone to failure just like any other mechanical method. We could verify connection quality if you provide some voltage measurements during anodizing.
Multiple pieces add in surface area, as you surmise.
|