Water-Soluble Sulfur Black：100% Black Uniform Powder Or Granule

Product Overview

Water-soluble sulfur black, designated under the Colour Index as C.I. Leuco Sulfur Black 1 with index number 53186, represents a significant advancement in sulfur dye technology. Unlike conventional sulfur blacks that require reduction with sodium sulfide prior to use, this product has been pre-reduced during manufacturing. As a result, it possesses the unique characteristic of dissolving directly in water, eliminating the need for harsh reducing agents and simplifying the entire dyeing process.

The product is manufactured according to the Chinese national standard GB/T 25809-2010, which is administered by the National Technical Committee for Dye Standardization and supervised by the China Petroleum and Chemical Industry Federation. The previous industry standard HG/T 3632-1999 was officially withdrawn in 2015, and all production now follows the national standard.

Physical and Chemical Properties

Water-soluble sulfur black appears as uniform black granules or a fine powder. It dissolves readily in water and, when dissolved in a sodium sulfide solution, exhibits a greenish-black coloration. When treated with concentrated sulfuric acid, the dye turns black while releasing sulfur dioxide gas; subsequent dilution causes precipitation.

From a chemical structural perspective, water-soluble sulfur black belongs to a class of high molecular weight compounds with a high sulfur content. Its molecular structure contains disulfide bonds and polysulfide bonds. Under certain conditions, these chemical bonds can be oxidized by atmospheric oxygen, generating sulfur oxides that further react with water molecules to form sulfuric acid. This chemical pathway is the primary cause of fiber tendering-the weakening and degradation of cellulose fibers-that has historically plagued conventional sulfur black dyeing.

Quality Specifications

The quality of water-soluble sulfur black is defined by several key parameters. In terms of appearance, the product must consist of uniform black granules or powder. The dyeing strength should be one hundred plus or minus three percent relative to the standard reference, ensuring consistent color yield between production batches. The spectral strength is similarly maintained at one hundred plus or minus five percent of the standard.

The shade of the dye, when compared to the standard, must achieve a rating of "approximate to slightly different," indicating very close color matching. Insoluble matter content must not exceed 0.5 percent, while moisture content is kept below 7.0 percent. Regarding solubility, the dye achieves at least sixty grams per liter at sixty degrees Celsius and can exceed one hundred sixty grams per liter at twenty-five degrees Celsius.

Color Fastness Performance

When applied to cotton fabric at a dyeing depth of six percent on the weight of fiber, which corresponds approximately to one over one standard depth, water-soluble sulfur black demonstrates specific fastness properties. Light fastness, tested under xenon arc lamp conditions, reaches grade six, indicating good resistance to fading from sunlight exposure.

Wash fastness at ninety-five degrees Celsius shows a color change rating of grade three, while staining on adjacent cotton fabric achieves a very good rating of grade four to five. Rubbing fastness is more moderate: dry rubbing achieves grade two to three, while wet rubbing reaches only grade one to two. This relatively low wet rubbing fastness is a characteristic limitation common to sulfur dyes.

Perspiration fastness, tested under both acidic and alkaline conditions, achieves grade four or higher. Hot pressing fastness at two hundred degrees Celsius produces a color change rating of grade four. It is important to note that these fastness values are specifically determined on cotton fabric. When the product is used for leather dyeing, the fastness standards applicable to cotton are not directly relevant.

Primary Application Areas

Water-soluble sulfur black finds application across several industries, with cotton textile dyeing being its most important use. The product is particularly well suited for continuous pad dyeing processes, where it provides uniform color application and good penetration. It can also be used in exhaust dyeing methods such as jigger and winch dyeing. Because the dye is pre-reduced, post-dyeing anti-tendering treatment is not required, effectively solving the common problem of fiber weakening associated with conventional sulfur blacks.

The product is also suitable for dyeing blended fabrics containing cotton with synthetic fibers such as polyester and nylon. Linen, viscose, vinylon, and their blends can all be dyed with water-soluble sulfur black. In the leather industry, the product is used for surface dyeing of chrome-tanned leather, producing a uniform black coloration. Additionally, it can be applied in dope dyeing processes for viscose fibers, allowing the color to be incorporated directly into the fiber structure.

Product Advantages

Compared with conventional sulfur blacks, water-soluble sulfur black offers several distinct advantages. The most notable benefit is ease of use, as the dye dissolves directly in water without requiring sodium sulfide for preparation. This simplifies the dyeing operation considerably.

The elimination of post-dyeing anti-tendering treatment represents both a process simplification and a cost saving. Because the dye is pre-reduced, the risk of fiber weakening is greatly reduced. The product also reduces environmental pollution by avoiding the use of sodium sulfide and lowering the sulfur content in wastewater. Good dyeing uniformity, stable shade, minimal batch-to-batch variation, and excellent storage stability compared to conventional powdered sulfur blacks are additional benefits.

Storage and Transportation Considerations

Water-soluble sulfur black has a strong tendency to absorb moisture from the air. Therefore, careful attention must be paid during storage and transportation. The product should be kept in a dry, well-ventilated warehouse, protected from direct sunlight. Exposure to heat and moisture must be avoided to prevent degradation of product quality. During transportation, packages should be handled gently to avoid damage. Typical packaging consists of iron drums lined with plastic bags, with a net weight of twenty-five kilograms per drum. Woven bags or cartons may also be used according to customer requirements.

Recent Developments

The water-soluble sulfur black product category continues to evolve. Environmentally friendly liquid sulfur black has been developed in recent years. This liquid form contains virtually no impurities, exhibits higher absorption rates than powdered products, and can improve dry and wet rubbing fastness by up to half a grade. Liquid sulfur black is fully oxidized during manufacturing, so it does not undergo further oxidation during transport or storage, providing greater stability. In Western industrialized countries, environmentally friendly liquid sulfur dyes have largely replaced powdered products.

Furthermore, the Chinese national standard GB/T 25809-2010 underwent review in August 2025, and the conclusion was that a revision is necessary. A new revision plan, designated as 20253798-T-606, is currently under review and will further standardize the product specifications for C.I. Leuco Sulfur Black 1.

Summary

Water-soluble sulfur black is an excellent black dye that combines deep color yield and low cost with improved convenience and reduced environmental impact. By offering pre-reduced, water-soluble form, it solves the key pain points associated with conventional sulfur blacks, including complex preparation procedures and fiber tendering. Whether applied in continuous pad dyeing of cotton textiles or in the dyeing of leather and viscose materials, water-soluble sulfur black demonstrates excellent versatility. As environmental requirements become more stringent and liquid dye technology continues to advance, the application prospects for water-soluble sulfur black products will become even broader.

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