The field guide · Colour and dye
Mordant
A mordant is a metal salt that binds a dye to the fibre and fixes the colour. Persian dyers used mainly alum (zāj); iron salts darken colours and are used for dyed browns and blacks. The same dye gives different shades with different mordants, and tannin-rich additions darken them further. Iron weakens wool over time, which is why iron-mordanted browns corrode.
Also mordanted · alum · zaj · iron mordant · iron-mordanted · ferrous sulphate
See also Corrosion, Oak gall, Madder, Natural dye
Sources
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