JOURNAL OF COSMETIC SCIENCE 294 Figure 2. U-shaped tube for experimental determination of zeta potential. A difference in the liquid levels was achieved as a result of electrophoresis. (1) Working part fi lled with the dye solution (2) main faucets (3) coupling fl uid parts and (4) balancing faucet.

ELECTROPHORETIC MOBILITY OF SOME TATTOO DYES 295 The dye solut ion level did rise in the “positive” bend (Figure 2, right side) for all four samples meaning that the dye grains for all colors used in the framework of our experi- ments acquired a negative charge when dissolved in the isotonic NaCl solution. ANALYSIS OF T HE ELECTROPHORETIC MOBILITY OF PIGMENTS Because the z eta potential of the black pigments was the largest, it was selected for the investigations related to applicability of electrophoresis to extract samples of “real” pig- ments samples from tissues. No human or animal tissue samples were used because of ethical restrictions and gelatin-based mixtures were used at that stage. Twenty-fi ve m illigrams of unbranded gelatin was dissolved in 500 mL of hot water to obtain such mixtures. Then the solution was divided into two parts one of them was left for cooling and hardening, whereas the required amount of the pigment suspension was added to the second one to make its concentration equal to 0.25 mL/L. Then it was also left for cooling and hardening. Parallelepipe dal samples were cut out of each part and placed into a plastic microelectro- phoretic cell (Figure 3). The cell was designed in such a way (12) that each sample was in contact with the graphite electrodes located on the outer edges of the cell and connected to an external electric power supply, whereas the inner sides of the samples were in con- tact with each other ensuring transferability of the dye particles between the samples. Figure 3. Microelec t rophoresis cell with the gelatin samples: (1) raw sample (2) the sample consisting some dye (3) graphite electrodes. Let us compare positions of the boundary between the colored and not-colored samples for various gelatin/black dye samples.