When an alkali-free glass is polished with a polishing liquid containing hydrofluoric acid as a main component, a sludge is generated on a glass surface and in a storage unit and a pipe of a polishing device. As a result, there arise problems such as deterioration of quality and stopping of the device. A washing liquid that dissolves a sludge containing aluminum and fluorine produced in a glass polishing device is characterized by containing Al3+ ions, and a sludge formed by bonding a divalent element such as Mg, Ca, Sr, and Ba with Al and F can be dissolved with this washing liquid. The problems are solved by washing the inside of the polishing device with this washing liquid.
