I’m no longer able to do this as I’m no longer working, but....putting glass pieces inside of a bigger glass container, fill the biggerco Rainer up with sulphuric acid submerging the glass piece by adding enough acid to cover it, place the container into a jewelry’s sonicator and turn that on for an hour.
it’s dangerous to do this (safety goggles, skirt and acid spill kit on hand) and really not practical outside of a lab, but this makes the glass cleaner than new.
Safest way to clean these hard to clean bubblers at home is with isopropyl alcohol (the greater the strength the better) and common table salt.
1) put a couple of tablespoons of salt inside your bubbler.
2) Add a few ounces of isopropyl alcohol and cover the openings (if possible) with a bit of Saran Wrap and a rubber band.
3) Shake until the isopropyl alcohol does not look like it’s going to get any dirtier and empty it. Add fresh isopropyl alcohol and repeat the shaking/draining process until it looks as lean as you want.
4) Fill the bubbler up with water, shake to dissolve any remaining salt and empty. Repeat with water until there is no visible salt left. Rinse once more.
The Isopropyl alcohol/salt is a good cleaner/gentle abrasive. This is actually sold on several formulas as ‘glass cleaner’, but it’s cheaper to cobble together the stuff yourself.
Tom