Fig. 1 depicts the amount of MB and R6G absorbed by bentonite against the equilibrium concentration of dye remaining in solution at room temperature. The initial dye concentration ranged from 5–100% of CEC. An S-shaped isotherm was observed at low dye loading while as the initial dye concentration increased equilibrium concentration of dye left in solution decreased and finally reached close to zero. With further increase of dye concentration, an H type isotherm was observed, indicating that the adsorbent surface has a very high affinity for dye molecules. The curves show plateaus corresponding to maximum adsorption of bentonite at around 220 mg/g for both dyes. The aforedescribed results are consistent with other reported research (for example, Atun et al., 2003). For preparation of fingerprint developer, initial dye concentrations for both MB and R6G were relative low, their position on the isothermal profile is shown by hollow symbols indicated by the arrow. Under these conditions, little or no dye was transferred to the supernatant liquid after dyed clay was washed in water and centrifuged. Attempts were then made to re-disperse the dyed clay into several different solvents including acetone, ethanol and tetrahydrofuran (THF). Samples were then centrifuged again to allow clay particles to settle. In each experiment, little to no dye was transferred to the supernatant solvent. This suggests good affinity between clay and doped dye, as suggested by other researchers including Narine and Guy (1981) who concluded that the bonding of cationic dye to clay minerals is an irreversible process. The amount of dye used in the dyeing procedure was much less than the CEC of the clay mineral particles, thus it is reasonable to expect little to none organic leaked from the dyed bentonite during further process and application.