Chrome Dye

Chrome dyes (also called chrome mordant dyes or metachrome dyes) use potassium dichromate as a mordant to fix synthetic dye compounds to wool. They produce particularly rich, deep colours, especially in the brown, navy, and dark green range, and are highly lightfast. They became widespread in Moroccan rug production from the mid-twentieth century.

Chrome dyes are not "natural" dyes, but they behave more like natural dyes than standard aniline dyes, they have good ageing characteristics and do not fade as rapidly or uniformly as cheaper synthetic dyes. A vintage piece with chrome dyes can age attractively. The trade-off is that potassium dichromate is a toxic substance, which has environmental and health implications in production contexts.