When selecting colors from the four-digit PMS metallic color guide, keep in mind that it is difficult to exactly match metallics on press to the color swatch. Metallic inks tarnish when introduced with chemically active PMS colors or the vehicle, which has an acid value. Metallic inks will go through levels of changes; most of the transition takes place 24 hours after the ink is mixed. To avoid changes of color within the same print job, ask your printer to mix the metallic ink several days to a week before the job is run so that the majority of the transition has taken place.