ASTM F1941 Specification

• In applications where the use of hexavalent chromium (Cr+6) is prohibited, coated fasteners with a supplementary chromate finish must be supplied with a trivalent chromium (Cr+3).
  Additionally, since yellow iridescence noted in the designation C of the Table 3 is characteristic of hexavalent chromium (Cr+6), the use of yellow dye with trivalent chromium (Cr+3) may be misleading and is not recommended