The replacement of chromium (111) by safer iron (11) has been investigated, using three commercial azo acid mordant dyes. These dyes have been applied to nylon 6 and wool fabrics and the dye exhaustion has been calculated at different temperatures. Color properties and fastness to light, washing and rubbing have been described. The characterization of the unmetallized and metallized dyes was investigated by HPLC analysis, thin layer chromatography, and UV/Vis spectroscopic techniques. Lightfastness shows that Fedye3 is a strong candidate for dyeing nylon 6 and wool fabrics with high lightfastness.