Microfade Testing of Fourteen Natural Dyes on Wool: A Comparison of Five Mordants

ABSTRACT Microfade testing (MFT) was used to examine standardized wool samples dyed with 14 natural historic dyes, each prepared with five different mordants, to determine whether the lightfastness and colourimetric properties of these dyes vary as a function of the mordant. The addition of mordants changed the original colour of the dyes as well as potential patterns corresponding to ΔL*, Δa*, and Δb* such that the variation of lightfastness ranges from 0.25–0.70 units of Blue Wool Equivalence (BWE). Disregarding the effect of mordants, MFT showed that all dyes have lightfastness equivalent to BW3, indicating that they belong in the category of ‘high sensitivity to light’. All dye-mordant combinations vary in lightfastness, such that even the least lightfast dye will have a mordant combination that is more lightfast than the most lightfast dye combined with a mordant that renders it less lightfast. The effect of mordants varies by dye: while one dye may demonstrate a difference in lightfastness of 0.56 units of BWE between the least and most lightfast mordant combination, another may show little or no difference (as low as 0.07 units of BWE). Overall, alum based mordants tend to produce the least lightfast combinations, followed by tin and iron, with copper and chromium producing the most lightfast combinations. This paper shows that there are no simplistic patterns of lightfastness between mordant-dye combinations with these 14 natural dyes. Identifying both dye and mordant is useful to better estimate the lightfastness of a dyed textile.