A Field Note on Sulphur Black for Modern Dyehouses

If you work in denim, you’ve met it. And if you color cotton knits for the mass market, you definitely live with it. To be honest, I’ve seen mills swear by Sulphur Black for decades because it hits that sweet spot: deep shade, rugged fastness, and sane cost. The one I’m reviewing here comes from HEBEI FUXIN INTERNATIONAL TRADE CO., LTD. (A-1205, MCC World Grand Plaza, 66 Xiangtai Road, Shijiazhuang 050023, China). I visited a buyer last month—small knitwear outfit—who said, “it just behaves,” which is rarer than you’d think.

Technical snapshot

• Name: Sulphur Black (also Sulfur Black; Sulphur Black 1)
• CAS No.: 1326-82-5; HS code: 32041911
• Molecular formula (trade reference): C6H4N2O5; structure: sulfur dye polymeric complex (practical handling)
• Appearance: black phosphorus-like flakes; or black liquid dispersion
• Typical substrates: cotton, viscose, modal, cotton/poly blends (cellulosic fraction takes the shade)

Process flow (real-world)

In practice, most mills run Sulphur Black on jigs, jets, or rope dye ranges. The chemistry is old-school but reliable:

1. Preparation: scouring/desizing to RRT ≤ 1% for uniform uptake.
2. Reduction: sodium sulfide/Na2S and sodium carbonate, 80–95°C, pH 10–11.
3. Dyeing: 20–60 min depending on depth (1–8% o.w.f.), salt optional.
4. Oxidation: air or H2O2/NaBrO3 to re-form the insoluble dye in-fiber.
5. Soaping & neutralization: remove unfixed; reduce rub-off.
6. Testing: fastness per ISO/AATCC, then shade approval.

Service life? Many brands rate 30–50 home launderings before noticeable dulling, though heavy abrasion (denim finishing) shortens that—nothing new there.

Product specification (typical)

Applications and advantages

• Denim warp dyeing and garment over-dyeing (great for cost-per-garment).
• Cotton fleece, tees, socks—where consistency matters.
• Advantages: economical deep blacks, robust wash fastness, easy shade control. And yes, the classic sulfur “charcoal” aesthetic is still in style.

Vendor comparison (condensed)

Customization and compliance

Custom options include flakes vs. liquid, tone adjustment (neutral/brownish/blueish), and concentration for low-liquor jet systems. Certifications: supplier can align with OEKO-TEX Standard 100 and ZDHC MRSL conformance on request; always verify with current COAs and MRSL declarations. For brands under REACH, ask for SVHC screening—standard practice now.

Case note (denim mill, South Asia)

A rope-dye line swapped to Sulphur Black liquid grade for a fashion black denim. Results after tuning oxidation: ISO 105-X12 wet rub improved from 3 to 3–4; re-dye rate dropped ≈18%. The finishing team said crocking “finally calmed down.” Not a miracle, just disciplined soaping and a cleaner reduction bath.

Testing standards and QC checklist

• ISO 105-C06 wash, ISO 105-X12 rub, ISO 105-B02 light
• AATCC 61, 8 for US buyers; ASTM E308 for color measurement
• Shade control via spectro: ΔE CMC(2:1) ≤ 0.8 for bulk lots (many customers aim tighter)

Final thought: for everyday black on cellulosics, Sulphur Black remains the pragmatic choice. It’s not glamorous, but it pays the bills—and keeps the returns team quiet.

References

1. ISO 105 series: Textiles—Tests for colour fastness. https://www.iso.org
2. AATCC Technical Manual: Colorfastness Methods. https://www.aatcc.org
3. ZDHC MRSL & Conformance Guidance. https://www.roadmaptozero.com
4. EU REACH Regulation (EC) No 1907/2006. https://echa.europa.eu