I have an antique crystal decanter with a narrow neck and there is some sort of stain, possibly soap scum, that I can't remove. I have tried white vinegar soaking, long bottle brushes, etc. but the stain doesn't come out.
Try dropping a denture cleaning tablet in water in the decanter. It always works well for me. Just leave it for awhile, I leave it overnight. Hope this helps you.
Try automatic dishwasher detergent.
If that doen't work, push a dryer sheet into the neck and soak in water.
Try putting some rice or a good amount of salt with a little bit of water. Shake it really good. That should give you a good scrubbing action.
Put crushed ice and salt in the decanter and swirl around...this will act as a scrubber and take care if it all! This also works well for coffee pots with a narrow opening!
Combinatio: I used a couple tablespoons of rice with a tablespoon of dishwasher detergent andabout a cup of water. A couple minutes of shaking and the dried port stains were gone from a fine heavy leaded decanter... thanks