You might try sloshing a little rinse aid for dishwashers inside it.

Are there spots on the inside of an overall haze? Spots may come out. Here’s one formula. Few drops of dish soap and 1/4 cup vinegar. Fill vase with long-cook rice and shake. Let rest shake again. If the inside is hazy, I’d say it was used as a vase and it’s hard water etching which is permanent. Let me know if this works.

Raw rice, not cooked

Oops wasn’t too clear. Raw and not instant as it swells. Thanks for the correction.

Denture clean tablets.

And a bottle brush