Welcome to the community @mansker. Yes, multiple passes can help in general for getting a deeper engrave or in this case, clearing away what you need to.
I’m pretty impressed that you were able to get to pens right away on the Glowforge.
Just a heads up on some forum customs and housekeeping. Since Glowforge is doing the unusual thing of offering support through the forum itself, they like to keep this category limited to machine problems and default settings on Proofgrade materials. So don’t be surprised if this gets re-categorized. You could change it yourself to Beyond the Manual.
Here is one topic that discusses settings for anodized aluminum. There are lots of topics on them, but other than basic settings, not much. Still there are posts that talk about this.