This paper investigates the feasibility of dyeing viscose rayon fabric with an anthocyanin solution extracted from H. sabdariffa L. calyces. For eco-friendly dyeing and improvement of the natural dye’s affinity to fabrics, natural mordants instead of traditional metallic mordants were applied. The effect of natural mordant types and mordanting procedures (pre-, meta- and aftermordanting) was evaluated by colorimetric measurement (CIE Lab and K/S values) and color fastness. Four natural mordants including alginate, walnut hull, lemon peel, and pinecone were used. The results show that the light and wash fastness (1–2 degrees according to the blue scale and the grayscale) of the un-mordanted viscose fabric were very low and unsuitable. Natural mordants, especially walnut husk and alginate, could improve color strength and color fastness. The light fastness value of the dyed fabric was improved, reaching a value of 5–6 in the presence of walnut, lemon, and pinecone mordants. The highest wash and light fastness was obtained when the aftermordanting method was used. Also, the use of walnut husk mordant increased the color strength and decreased the lightness of the dyed fabrics, as compared to other natural mordants, in all three methods of mordanting
