GB/T 4469-2006 "Vat Dyes—Determination of Rate of Reduction—Steaming Method" specifies the method for determining the reduction rate of vat dyes using the steaming method, which is applicable to the pad dyeing process of vat dyes (ultrafine powder) suspensions. The dye suspension is padded onto the fabric, followed by drying, padding with a reducing solution, and steaming for different durations. The reduction rate is determined by visually comparing the normal color development corresponding to the steaming time. The test requires instruments such as a steaming box, padding machine, soaping equipment, and an oven to ensure the stability of the reduction effect in the dyeing process.