We ran 8 test pieces of 2011, all of them were getting a "shadow" and these pictures can show somewhat of a timeline of our progress and how we solved the solution.
The pieces start left to right.
Part # / Anodize Time
1 83 min
2 75 min
3 64 min
4 45 min
5 60 min (no etch/desmut)
6 40 min (no etch/desmut)
7 35 min (no etch/desmut)
8 25 min (no etch/desmut)
9 25 min (part was test piece #1 going for round 2 so we could see how the metal would react to multiple runs. Stripped for 3 min desmut - 3 min)
Pieces 1-4
Pieces 5-8
We never had an issue with any type of shadowing on 6xxx.
Overall on the 2011, we had the most luck with splash when the anno times were kept low, and we did not etch or desmut. Parts 8&9 were the best.
Kinda off topic, I know. However, since the conversation and topic of shadowing was brought up, I thought I would chime in.