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Azoic dye- process, properties and blinding of colors

 Azoic dyeing Process sequence: 

Scoured or Bleached yarn 




Squeezing (hydro-extraction) 






Rinsing with 1 gpl of HCl 


Soaping at boil 


Washing, squeezing and Drying 


(A) Naphtholation recipe: 



(1) Naphthol

1 gpl

(2) Wetting agents

1 gpl

(3) Caustic soda (70 °Tw)

1.5 to 2.5 gpl

(4) Temperature

Room temperature

(5) MLR



20 to 30 minutes

(B) Developing bath recipe: 



(1)Fast base

1 gpl

(2)HCl (32 °Tw)

1 ml/l

(3) Sodium Nitrite

0.5 gpl

(4) Sodium acetate

1 gpl

(5) Aluminium sulphate

1 gpl

(6) Temperature

Room temperature




10 to 15 minutes

(C) Soaping recipe: 




2 to 3 gpl

(2)Soda ash

1 to 2 gpl

(3) Temperature



30 minutes

Azoic dye- process, properties and blinding of colors

Fastness properties of Azoic Dyes: 

(1) The very stable electron arrangement in azo dyes is accountable for their good to excellent to exceptional light fastness, which is rated 6 to 7 for these dyes.
(2) Due to azoic dyes' insoluble nature in water, their washability is additionally quite good. 
(3) Because insoluble azoic dye builds au fait the surface of the fibre, azoic dyes have poor rubbing fastness. a radical soaping will help with this.
(4) Azoic dyes occasionally have a blinding effect (matt or delustred effect). this can be because the distribution of the dye clusters within the fibre polymer isn't uniform. 

Stripping of Azoic Dyes:

In the presence of a cation-active chemical like Lissolamine A, sodium hydrosulphite removes the dye most efficiently (acetyl trimethyl ammonium bromide). 

The products are treated at the boil for about a quarter-hour during a liquor made of 2% Lissolamine A and 12% hydrated oxide with a 72"Tw strength (32.5 percent). 

After that, the temperature is lowered to only below boiling, and 5–6% of sodium hydrosulphite is added. 

After another 30 to 45 minutes, the alcohol is fled, and germicide bleach is employed to end the stripping process. 

Blinding of Azoic Colors: 

A non-lustrous appearance can occasionally be obtained on cotton and rayon when using azoic dyes. 

The delustered or matte effect is stated as "blinding," because it can alter how the colour appears. 

In dark colours, this phenomenon happens more frequently. it's known that when the pigment on fabric isn't evenly distributed throughout the cellulose, it agglomerates into larger particles and causes blindness. 

After coupling, the effect doesn't become apparent right once but instead manifests itself after standing or more frequently while rinsing, washing, and soaping, particularly at high temperatures. 

Due to the improved molecular mobility caused by elevated temperature, especially in alkaline conditions, aggregation is inspired. 

Those dyes that are liable to aggregation should be washed at temperatures between 40 and 60 degrees Celsius. 

When soaping is finished in neutral conditions, better results are attained. However, different azoic mixtures behave differently when it involves blindness. 

Azoic dye
Azoic dye

Questions -

  1. Describe the process sequence of azoic dyeing.
  2. Mention the recipe for the azoic dyeing process for all three stages.
  3. Which are the fastness properties of azoic dye?
  4. Explain the stripping action of azoic dye.
  5. What is the blinding of azoic dye colours?


Definition of AZOIC DYE. (n.d.). from

Dyeing of cotton fabric with azoic dyes. (2020, April 25). Textile Study Center.

Patwary, E. M. Z. (2012, April 25). What is azoic dye. Textile Fashion Study; Engr. Mohammad Zillane Patwary.

Sayed, A. (n.d.). An overview of Azo dyes. from

Textile Knowledge. (n.d.). from

Yamaguchi, Y. (1956). Azoic Dyes. Journal of Synthetic Organic Chemistry Japan14(4), 239–245.

Continue read,

Part 1 Introduction of azoic dye

Part 2 Azoic dyeing procedure

Part 3 Azoic dye- process, properties and blinding of colours

Writer - Rushikesh Patil (Textile Engineer)
(DKTE Society textile engineering college ichalkaranji)
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