The substantivity of reduced sulfur dyes
is high partly because of the high concentration
of salts in the reducing baths, but,
parallel to direct and leuco vat-dye anions,
this substantivity varies from dye to dye
and can always be increased by the addition
of common salt or sodium sulfate.
Reduced sulfur liquids generally dye so
rapidly that their addition is made gradually
and at low temperatures.