Acetone finishing

Has anyone used an ultrasonic humidifier to create a vapor rather than heating?

That's actually a good idea, but you will need something to diffuse the mist evenly.

Not sure if the plastic that the humidifiers are made with will dissolve or not but the ultrasonic vaporizer is metal. My idea would be to use it like a paint gun, cool the part then paint the part with the vapor spewing from the humidifier. The acetone should condense evenly on the cooled part, let dry and you're done.

The other benefit would be that the vapor cuts on and off with the flip of a switch. Those humidifiers are instantaneous, as soon as you flip the switch vapor is pouring out and it's cool(you can get heated ones too, but those take a while to hear up). Flip a switch and vapor is off and your remaining acetone is at room temp.