The side of lettering is very important! If there are scratches on the luminous side, it can still be used, but if there are insertion marks on the lettering side, the CD can't be used. Because the lettering side is used to reflect light, the principle is the same as that of a mirror. The mercury on the back of the mirror can't be used if it is damaged, so the lettering surface is protected with the commonly used CD protective film.