Quick question: Would a really soft Makeup brush meant to apply powders work to lift some of the dust (and then dump it over a vacuum machine so it’s actually removed) or is it not fine enough?
I wouldn’t risk using a brush of any kind. Can of air and bed the straw so the can is upright or use pec pads. There are instructions on cleaning the mirror and galvos if needed on the Formlabs site.
As Ken said, any non-approved cleaning materials that come into contact with the mirror surface risk damaging it. This is because these are “first surface” mirrors and have no protective coating over them.