Streaks on hard anodize surface

What would cause a wood grain appearance on hard anodized parts? It looks like streaks of thick anodize over flash hard anodize. Hard anodize should have a granular dark look, but this one is definitely different. Any ideas?

Mario Rodriguez
- Phoenix, Arizona, USA

Can you verify if the anodize is the same thickness over the entire part? I have seen grain on anodized aluminum which seemed to be grain structure, but which had some swirl to the pattern which I might have thought looked like woodgrain. Can you strip the anodize, then etch the aluminum using some laboratory etch which would develop the grain?

Tom Pullizzi
Falls Township, Pennsylvania

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