The use of a range of ultrasound frequencies to reduce colouration caused by dyes.

The formation of hydrogen peroxide and the degree of decolourisation of six different dyes as a result of sonication over several ultrasonic frequencies (20, 40, 380, 512, 850, 1,000 and 1,176 kHz) was investigated and correlated. It was found that the highest levels of hydrogen peroxide and also the greatest amount of decolourisation occurred at 850 kHz. 380 and 512 kHz also resulted in some decolourisation, however higher and lower ultrasonic frequencies were not effective.