THE EFFECT OF ALUMINUM HYDROXIDE DISSOLUTION ON THE BLEEDING OF ALUMINUM LAKE DYES

The effect of pH on the bleeding of FD&C yellow No. 5 aluminum lake an d FD&C red No. 40 aluminum lake was investigated. The pH-bleeding prof iles corresponded to the pH-solubility profile of aluminum hydroxide. The similarity of the bleeding profiles of both lake dyes and the pH-s olubility profile of aluminum hydroxide indicates that pH related blee ding, other than that occurring by competition with anions, is a resul t of dissolution of the aluminum hydroxide substrate. This dissolution is related to the properties of the substrate rather than to the stru cture of adsorbed dye.