Rinse the cloth bag first, then put it in a basin of clear water, soak it in some dark blue ink, gently rub it for half a minute, and then take it out and dry it directly. Because blue ink spindle blue pigment can promote the recovery of fluorescent whitening agent in white cloth bag, it can also be soaked in hot rice washing water and wiped with orange peel after boiling. Principle: It can also promote the recovery of fluorescent whitening agent in white cloth bag.