Soda blasting seems to be the way the professionals do it, but you'd need to find a professional. If you do go with media blasting, you want to use something that will clean off completely. I've heard ultrasound in a solvent bath is great, but I've never found anybody with the equipment near me. Most of us use the shade-tree approach of an escalating series of solvents/cleaners (Simple Green is pretty low on this scale) and various abrasive pads like scotchbrite. Work hard enough and you can do a reasonable job and what's left typically looks good as patina. I've heard using steel wool on alum is considered a no-no, but it works great on steel parts.