A Field Note on Sulphur Black: The Workhorse Dye That Refuses to Fade Away

If you’ve spent time in a denim mill—or frankly any cotton plant—you know the quiet dominance of Sulphur Black. It’s not flashy, but it’s reliable, economical, and increasingly, cleaner. Originating from HEBEI FUXIN INTERNATIONAL TRADE CO.,LTD. (A-1205, MCC World Grand Plaza, 66 Xiangtai Road, Shijiazhuang 050023, China), this grade has been turning heads in mills that want deep shade without drama.

What’s Trending

Two shifts are defining Sulphur Black right now: liquid, low-sulfide versions for cleaner effluent, and tighter compliance (ZDHC MRSL, REACH). Mills tell me shade reproducibility has quietly improved with premixed liquid forms—less tinkering on the floor, fewer do-overs.

Technical Snapshot

Process Flow (what mills actually do)

• Materials: Sulphur Black flakes or liquid; sodium sulfide; caustic; wetting and sequestering agents; salt (optional).
• Vatting: Reduce at 80–95°C to the leuco form—this is where shade potency is won or lost.
• Dyeing: Cotton/viscose at liquor ratio 8:1–15:1, 30–60 min depending on depth.
• Oxidation: Air, H2O2, or sodium nitrite to lock color.
• After-treat: Soaping at 95°C, then neutralize; softener as needed.
• Testing standards: ISO 105-C06 (wash), ISO 105-B02 (light), AATCC 8/165 (rubbing/accelerated aging).

Typical fastness (internal and customer lab notes): washing 4–5; light 5–6; rubbing 3–4 dry / 2–3 wet. Service life on garments: around 50–100 home launderings before perceivable fade, depending on finishing and detergent chemistry.

Where it shines

Denim warp, workwear twills, yarn dye for socks, and some nonwovens. Many customers say it “just runs” on their existing lines—no exotic auxiliaries, no sticker shock.

Advantages (why buyers keep coming back)

• Deep jet black with competitive gram-per-shade economics.
• Stable liquor; good levelness on both rope and open-width.
• Compliance-ready batches available (ZDHC MRSL, REACH-aligned), according to vendor declarations.

Vendor landscape (quick comparison)

Customization

FUXIN offers flakes for cost-focused setups and a liquid for tight shade control. Customizations I’ve seen: viscosity tuned for dosing pumps, pre-reduced blends for lower sulfide discharge, and shade calibration packs for denim labs.

Case notes from the floor

• Bangladesh denim mill: Switched to low-sulfide liquid Sulphur Black; internal wastewater logs showed ≈18% COD and ≈40% sulfide reduction; first-time-right increased by 12% month-on-month.
• EU workwear converter: Reported wash fastness 4–5 (ISO 105-C06 C2S) and light fastness 5–6 (ISO 105-B02); garments retained acceptable depth after ~80 home washes.

To be honest, the reason mills keep using Sulphur Black is simple: it’s the best value route to durable black on cotton—especially when the liquid grades meet modern compliance.

Certifications and paperwork

Ask for ZDHC MRSL conformance declaration, REACH compliance statement, and recent wastewater test data against ZDHC guidelines. Also, lab test to ISO 105 and AATCC standards before bulk, just to be safe.

References

1. ISO 105 Textiles—Tests for colour fastness (C06, B02, X12).
2. AATCC Technical Manual: Methods 8, 61, 165.
3. ZDHC Wastewater Guidelines and MRSL v3.1.
4. REACH Regulation (EC) No 1907/2006—Annex XVII restrictions.