Stable, pourable aqueous suspensions of solid particulate materials are provided, especially suspensions of sulfur dyes which are characterized a very low content of inorganic sulfides and inorganic polysulfides. The suspensions are produced using certain suspension stabilizing agents, particularly polysaccharides, such as xanthan gum, whose solutions in water are pseudoplastic. The suspensions may further comprise a non-sulfide reducing agent. An improved method is also provided for determining the the potential for such suspensions to release hydrogen sulfide upon being acidified at a given temperature, which method comprises acidifying a sample of the suspension to pH 2.9-3.7, capturing all of the hydrogen sulfide released during acidification in aqueous alkali and measuring the sulfide ion content of the aqueous alkali.