Create a mixture of one-half tablespoon mild liquid dish soap and 4 cups warm water. Stir the water and dampen a soft cloth with the soapy mixture.
Wipe down the ceramic vase to remove any dust, dirt and debris. Dry the vase with a soft cloth.
Create a paste with one-half cup boric acid powder, which is available in your grocery’s laundry aisle, two tablespoons table salt and one tablespoon lemon juice. Stir the ingredients until they are well incorporated, adding a small amount of water if the paste is too thick.
Spread the paste onto the ceramic rust stains with your fingers. Allow the paste to penetrate the rust for at least three hours before wiping it away with a damp soft cloth.
Wipe down the ceramic vase with a soft cloth to remove any remaining moisture.