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Dye thickness in anodize

I laser etch into black anodized aluminum nameplates. I am concerned about the depth I am etching. We etch to remove the dyed layer. It seems that some lasers make a whiter mark, others look a little grey or dirty. How far into the anodizing does the dye go? Are we affecting the integrity of the anodizing when we remove the black dye layer?

Karl M [last name deleted for privacy by Editor]
Laser Engraver - Wichita, KS, USA
2004

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2004

How deep the dye layer goes depends on how thick the anodizing is, Karl. Dye does not go on top of anodizing, it goes into the anodizing. It is always risky to guess, but the anodizing on quality black parts is probably about .0006" to .001" thick. There is a non-porous boundary layer at the base of the anodizing, but this is quite thin; so for practical purposes the dye layer is the thickness of the anodizing. If you remove the dye layer, you destroy the anodizing.

You can protect the damaged area with a chromate conversion coating, but the ideal thing to do is to mark the parts differently, i.e.., silk screen them before anodizing or mask the dye out of selected areas before sealing, etc. I don't have personal experience with them, but there are viscous dyes nowadays that can be applied with some sort of roller coating, so that you could apply the white dye numbers that way before you dyed the rest of the part black.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey