Acid Black 2

Acid Black 2 appearance is black with glittering particles. It is soluble in water and blue-violet, soluble in ethanol and blue. The dye is blue in concentrated sulfuric acid, and it is purple after dilution and forms a precipitate. The aqueous solution plus sodium hydroxide has a dark purple precipitate.

TRADE NAME:Nigrosine Black,Acid Nigrosine,Nigrosine water soluble,Acid Grains Black,Nigrosine Black 2 Nigrosine MS Conc,Water-soluble Nigrosine Black Shoe polish black,Nigrosine W/S,Nigrosine WLL,Nigrosine B,Nigrosine G.HN,Nigrosine K,Nigrosine S,Nigrosine Z,Water Nigrosine SB

Key features

• Red-black to black powder, produces deep black shades
• Good water solubility — easy to disperse in aqueous baths
• Strong affinity for protein fibres (wool, silk) and nylon
• Fastness profile: generally good lightfastness; variable wash-fastness depending on substrate and after-treatment
• Used in leather dyeing, textile (wool/silk/nylon) dyeing, water-based inks and paper
• Compatible with acid dyeing processes (acidic dyebaths) and common leveling agents
• Requires standard industrial handling precautions (avoid dust, use PPE)

Technical Specifications

• ‍CAS NO: 8005-03-6
• CI.NO: 50420
• Molecular Formula: C22H14N6O9S2-3.2[NA]
• Molecular Weight: 616.49
• Shade:Black‍

Colour Fastness Test

Application:

Acid Black 2 mainly used for dyeing leather. It is also suitable for dyeing paper, wood, soap, anodized aluminum, wool, silk, and also for making ink.

FAQ

How does Acid Black 2 attach to wool and nylon fibers?

Acid Black 2 is an anionic dye that binds primarily by electrostatic attraction to positively charged (protonated) amino groups on protein fibers (wool, silk) and on nylon. Hydrogen bonding and van-der-Waals forces provide additional fixation; the process is run under mildly to strongly acidic conditions to maximize ionic attraction. 

What dyebath conditions give the best levelling and depth?

For levelling acid dyes a mildly acidic bath (commonly pH ~2.0–4.5) is typical; exact pH, temperature and salt/acid program depend on fiber and dye class. Start with a small lab sample: raise temperature gradually (often up to 80–95°C for wool/nylon processes) while maintaining target pH, then cool and rinse thoroughly. Always validate on a lab swatch before production. 

What practical recipe can I start with for wool (starter lab recipe)?

A conservative starter formula for lab trials: 1–3% owf (on-weight-of-fiber) Acid Black 2, liquor ratio 1:20, acidify to pH ≈ 4 with acetic acid or citric acid, heat slowly to 80–90°C over 30–45 minutes, hold 20–30 minutes, cool and rinse until clear. Adjust %owf, time and pH based on shade and fastness testing. (This is a general starting point — adjust and perform lab tests for your substrate.) 

How does Acid Black 2 perform vs. other black dyes (fastness & shade control)?

Acid Black 2 gives deep black shades with good wet fastness on protein fibers and nylon, but overall lightfastness and rubbing fastness depend on shade depth and substrate; some formulations use blends or milling classes to improve fastness. For outdoor/exterior permanence or top-grade lightfastness, consider testing alternative blacks or mixture strategies.

Are there environmental or disposal concerns?

Acid dyes are synthetic organics that can appear in effluent if not captured; dyehouse wastewater requires appropriate treatment (adsorption, flocculation, or biological treatment depending on local regulations). Avoid releasing concentrated dye waste to sanitary sewers and follow local disposal and chemical handling regulations. Consult your MSDS and local authorities. 

How should I store and handle Acid Black 2 in the plant?

Store in a cool, dry, well-ventilated area in tightly closed containers. Avoid contact with strong oxidizers. Use appropriate PPE (gloves, goggles, dust mask for powders); for fine powders control dust to reduce inhalation and combustible dust hazards. Refer to the supplier MSDS for exact safety data.