Water stain craftsman Insesame

Limescale is formed when minerals in water precipitate, but it's no exaggeration to say that the final boss of all limescale is silica-based limescale called silicon dioxide. This is silica scale.

This stain doesn't just adhere to the surface, but rather bonds with the silica components in glass and glaze, so it can't be removed with alkaline or acidic solutions.
You need to break that bond.

Limescale Shokunin is Japan's first acidic powder cleanser.
The acid dissolved in water removes excess scale from around the silica, and several types of abrasives intricately intertwine to release the bonds.

You can adjust the strength of the cleanser by changing the amount and water, so it can be thoroughly removed by hand or with a polisher.