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How to identify which dye is used on textiles?
Nov 19, 2018


Determine the principle of the simple identification method




According to the dyeing principle of dyes on textiles, the common types of dyes for common textile fabrics are as follows:


Acrylic fiber-cation dye


Nylon and protein fiber - acid dye


Polyester and other chemical fiber-disperse dyes


Cellulose fibers - direct, sulfurized, active, reduced, nafto, paint and anthraquinone dyes


For blended or interwoven textiles, the type of dye is used for its components. For example, for polyester and cotton blends, the polyester component is a disperse dye, and the cotton component is separately made using the corresponding dye types, such as dispersion/ Activity, dispersion/reduction process, etc.



1 sampling and pre-treatment

The key steps in identifying the type of dye on cellulose fibers are sampling and pretreatment of the sample. When taking the sample, take the same dye part, such as the sample contains several shades, each color should be taken. If fiber identification is required, the fiber type should be confirmed according to the FZ/TO1057 standard. If the sample is attached with impurities, grease and slurry that affect the experiment, it must be treated with a cleansing agent in hot water at 60-70 °C for 15 minutes, washed and dried. If the sample is known to be finished by resin, it is treated separately by the following method.


1) Urine resin was treated with 1% hydrochloric acid at 70-80 ° C for 15 min, washed and dried.


2) Acrylic resin The sample can be treated by refluxing with 50-100 times of dihydrazine for 2-3 hours, taken out and washed and dried.


3) The silicone resin can be treated with 5g/L soap and 5g/L sodium carbonate 90cI=15min, washed and dried.

2 Direct dye identification method

The sample was boiled with 5 to 10 mL of an aqueous solution containing 1 mL of concentrated aqueous ammonia to sufficiently extract the dye.


The extracted sample was taken out, and 10-30 mg of white cotton cloth and 5-50 mg of sodium chloride were placed in the extract, boiled for 40-80 s, left to cool, and washed with water. If the white cotton cloth is dyed to almost the same color tone as the sample, then it can be concluded that the dye used for dyeing the sample is a direct dye.




3 sulphur dye identification method

Place 100-300mg sample in 35mL test tube, add 2~3mL water, 1-2mL 10% sodium carbonate solution and 200-400mg sodium sulfide, heat to boil for 1-2min, take out sample 25-50mg white cotton cloth and 10-20mg Sodium chloride in a test tube. Boil for 1-2 min. Remove and place on filter paper to reoxidize it. If the obtained color light is similar to the original color, only the difference in depth may be considered as a sulfurized or sulfurized vat dye.


4 Identification method of vat dye

Place 100-300mg sample in 35mL test tube, add 2-3mL water and 0.5-lmL 10% sodium hydroxide solution, heat to boil, then add 10-20mg insurance powder, boil 0.5-lmin, take out the sample and put into 25- 50 mg of white cotton cloth and 0-20 mg of sodium chloride, continue to boil for 40-80 s, and then cooled to room temperature. Remove the cotton cloth and place it on the filter paper for oxidation. If the color after oxidation is similar to the original, it means that the vat dye is present.

5 Nafto dye identification method

The sample was boiled in 100 times the amount of 1% hydrochloric acid solution for 3 min, washed thoroughly, and boiled for 5 min with 1% ammonia water 5-10 mL. If the dye was not extracted or the amount of extraction was small, it was treated with sodium dithionite. After discoloration or discoloration, even if it is oxidized in the air, the primary color cannot be restored, and it is not possible to confirm the presence of metal. In this case, the following two tests can be performed. If the dye can be extracted in the test of 1), and 2) In the test, the white cotton cloth was dyed yellow and fluorescing, and it was concluded that the dye used in the sample was a nafto dye.


1) Place the sample in a test tube, add 5 mL of pyridine and boil it to see if the dye is extracted.


2) Place the sample in a test tube, add 2 mL of 10% sodium hydroxide solution and 5 mL of ethanol, boil, then add 5 mL of water and sodium dithionite, and boil to reduce it. After cooling, filter, put white cotton cloth and 20-30 mg of sodium chloride into the filtrate, and boil for 1-2 min. After cooling, remove the cotton cloth and observe whether the cotton cloth emits fluorescence when irradiated with ultraviolet rays.


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