1. Similar to direct dyes
(1) Use salt to promote dyeing
(2) Cationic fixing agent and metal salt fixing agent to improve color fastness
2. Similar to vat dyes
(1) The dye needs a reducing agent to be reduced to a leuco body before it can be dyed on the fiber and oxidized on the fiber. It's just that the strong reducing agent sodium sulfate is not used, but the weak reducing agent sodium sulfate. However, the directness of leuco body to fiber after reduction is lower than that of vat dyes, and the tendency of dyes to aggregate is greater.
(2) With acid, it can generate H2S gas, and with aluminum acetate, it can produce black aluminum sulfide precipitation (used to verify the presence of sulfur dyes)