Introduction
It is necessary to identify what type of dyes are used in a sample before dyeing it. Shades or tones will not match accurately if the dye type doesn’t match. Only chemical tests confirm the type of dye used for dyeing. But for some materials the type of dye is fixed, for example, polyester is almost always dyed with a dispersed dye. So in this case no test is necessary to test the dyed polyester sample. But if we use this logic in the case of polyester-cotton blends then this may give the wrong result. So it is essential to test the material for the identification of the dye.
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| Dyestuffs |
Apparatus
- Test tube
- Burner
- Pipette
- Stopwatch
- Chemicals
- Tannin mordant cotton etc.
- Sample: Dyed fabric sample.
Test: 01 (Direct dye)
| Observation | Inference | Remarks |
|---|---|---|
| Color of the Sample destroyed |
Maybe direct, Basic and Acid Dyes |
Absence of vat, sulfur, Reactive or naphthol dyes |
| Observation | Inference | Remarks |
|---|---|---|
| The color bleeds and white cotton is dyed |
Absence of acid or basic color |
Direct dyes are conformed |
Result: 01: The dyed sample is dyed with direct dye.
Test: 02 (Acid dye)
| Observation | Inference | Remarks |
|---|---|---|
| Color of the Sample destroyed |
Maybe direct, Basic and Acid Dyes |
Absence of vat, sulfur, Reactive or naphthol dyes |
| Observation | Inference | Remarks |
|---|---|---|
| The color bleeds, the dyeing is partially or totally stripped and the white Cotton is a little or not stained and white Cotton can be rinsed perfectly clean again in water |
Acid or basic color | Absence of direct dye |
Experiment no: 03: The sample is warmed (up to 60℃) with methylated spirit and a few drops of acetic acid and then it is diluted with water wormed with a piece of tannin mordanted cotton and a piece of cotton.
| Observation | Inference | Remarks |
|---|---|---|
| Tannin mordanted cotton is not dyed, white cotton may be dyed may not be dyed |
Absence of basic color | It may be the presence of acid dye |
Experiment no: 04: The sample is boiled with a 5% soap solution and is acidified with a few drops of acetic acid and boiled with a piece of wool or silk fabric.
| Observation | Inference | Remarks |
|---|---|---|
| Colour is transferred to White wool/silk fabric/fiber but it's not like that in direct dye |
Absence of basic dye | Acid dye is confirmed |
Result: 02: The dyed sample is found to be dyed with acid dye.
Test: 03 (Basic dye)
| Observation | Inference | Remarks |
|---|---|---|
| The color of the sample was destroyed | May be direct, basic, or acid dyes | Absence of vat, sulphur, Reactive or naphthol dyes |
| Observation | Inference | Remarks |
|---|---|---|
| The color bleeds, the dyeing is partially or totally stripped and the white cotton is a little or not stained and white Cotton can be rinsed perfectly clean again in water |
Acid or basic color | Absence of direct dye |
| Observation | Inference | Remarks |
|---|---|---|
| Tannin mordanted cotton is dyed | Absence of acid dye | The basic dye is confirmed |
Result: 03: The dyed sample is found to be dyed with basic dye.
Test: 04 (VAT, indigo dye)
Experiment no: 01: Boil with the soap solution and NH4OH solution for 1 minute.
| Observation | Inference | Remarks |
|---|---|---|
| No change | Maybe vat, sulphur, Reactive or naphthol dyes |
The absence of direct, basic and acid dye |
Experiment no: 02: The sample is boiled with 5% NaOH solution and a pinch of hydrose.
| Observation | Inference | Remarks |
|---|---|---|
| Colour is destroyed and reappears on washing or airing. But in this case color is not totally destroyed |
Absence of reactive or naphthol | Maybe VAT or sulfur dye present |
Experiment No: 03: The sample is boiled in a test tube with SnCl2 10% solution and a few drops of HCl. The mouth of the test tube is covered with blotting paper moistened with 1 – 2 drops of Pb- Acetate solution.
| Observation | Inference | Remarks |
|---|---|---|
| Black spot on Pb – acetate paper not found |
Absence of sulfur dye | VAT dye may be present |
Experiment No: 04: The sample is warmed with chloroform or benzene in a dry test tube.
| Observation | Inference | Remarks |
|---|---|---|
| Colored solution | Absence of vat anthraquinone | Presence of vat indigo |
Result: 04: The dyed sample was found to be dyed with VAT (indigo) dye.
Test: 05 (VAT, anthraquinone dye)
Experiment no: 01: Boil with the soap solution and NH4OH solution for 1 minute.
| Observation | Inference | Remarks |
|---|---|---|
| No change | Maybe vat, sulphur, Reactive or naphthol dyes |
Absence of direct, Basic and Acid Dyes |
Experiment no: 02: The sample is boiled with 5% NaOH solution and a pinch of hydrose.
| Observation | Inference | Remarks |
|---|---|---|
| Colour is destroyed and reappears on washing or airing. But in this case color is not totally destroyed |
Absence of reactive or naphthol | Maybe VAT or sulfur dye present |
Experiment No: 03: The sample is boiled in a test tube with SnCl2 10% solution and a few drops of HCl. The mouth of the test tube is covered with blotting paper moistened with 1 – 2 drops of Pb- Acetate solution.
| Observation | Inference | Remarks |
|---|---|---|
| Black spot on Pb – acetate Paper not found |
Absence of sulfur dye | VAT dye may be present |
Experiment No: 04: The sample is warmed with chloroform or benzene in a dry test tube.
| Observation | Inference | Remarks |
|---|---|---|
| No colored solution | Absence of vat indigo | Presence of vat anthraquinone |
Result: 05: The dyed sample was found to be dyed with VAT (anthraquinone) dye.
Test: 06 (Sulphur dye)
Experiment no: 01: Boil with the soap solution and NH4OH solution for 1 minute.
| Observation | Inference | Remarks |
|---|---|---|
| No change | Maybe vat, sulphur, Reactive or naphthol dyes |
Absence of direct, Basic and Acid Dyes |
Experiment no: 02: The sample is boiled with 5% NaOH solution and a pinch of hydrose.
| Observation | Inference | Remarks |
|---|---|---|
| Colour is destroyed and reappears on washing or airing. But in this case color is not totally destroyed |
Absence of reactive or naphthol | Maybe VAT or sulfur dye present |
Experiment No: 03: The sample is boiled in a test tube with SnCl2 10% solution and a few drops of HCl. The mouth of the test tube is covered with blotting paper moistened with 1 – 2 drops of Pb- Acetate solution.
| Observation | Inference | Remarks |
|---|---|---|
| Black spots on Pb – acetate paper | Absence of vat dye | Presence of sulfur dye is confirmed |
Result: 06: The dyed sample was found to be dyed with sulfur dye.
Test: 07 (Naphthol dye)
Experiment no: 01: Boil with the soap solution and NH4OH solution for 1 minute.
| Observation | Inference | Remarks |
|---|---|---|
| No change | Maybe vat, sulphur, Reactive or naphthol dyes |
Absence of direct, Basic and Acid Dyes |
Experiment no: 02: The sample is boiled with 5% NaOH solution and a pinch of hydrose.
| Observation | Inference | Remarks |
|---|---|---|
| The Colour was destroyed and did not come back to washing and airing. |
Absence of VAT and sulfur | Absence of VAT and sulfur |
| Colour remains unchanged | Absence of VAT and sulfur | May be reactive or naphthol dyes present. Or maybe the Azo content dyestuffs restricted in Europe |
Experiment no: 03: The sample is dissolved in cold concentrated H2SO4 and then diluted with water.
| Observation | Inference | Remarks |
|---|---|---|
| Pink coloration | Absence of reactive dye | Naphthol may be present |
Experiment No: 04: The sample is warmed in a dry test tube with chloroform or benzene.
| Observation | Inference | Remarks |
|---|---|---|
| Pink coloration | Absence of reactive dye | Naphthol may be present |
Experiment No: 05: The sample is treated with cold concentrated H2SO4 and diluted with water carefully sliding it into the test tube.
| Observation | Inference | Remarks |
|---|---|---|
| Ring formation between the junctions of a layer of water and H2SO4 |
Absence of reactive dye | Naphthol present confirm |
Result: 07: The dyed sample was found to be dyed with naphthol dye.
Test: 08 (Reactive dye)
Experiment no: 01: Boil with the soap solution and NH4OH solution for 1 minute.
| Observation | Inference | Remarks |
|---|---|---|
| No change | Maybe vat, sulfur, Reactive or naphthol dyes |
Absence of direct, Basic and Acid Dyes |
Experiment no: 02: The sample is boiled with 5% NaOH solution and a pinch of hydrose.
| Observation | Inference | Remarks |
|---|---|---|
| The Colour was destroyed and did not come back to washing and airing. |
Absence of VAT and sulfur | May be reactive or naphthol dyes present. Or maybe the Azo content dyestuffs restricted in Europe |
| Colour remains unchanged | Absence of VAT and sulfur | May be reactive or naphthol dyes present. Or maybe the Azo content dyestuffs restricted in Europe |
Experiment No: 03: The sample is dissolved in cold concentrated H2SO4 and then diluted with water.
| Observation | Inference | Remarks |
|---|---|---|
| No pink color | Absence of naphthol color | Reactive dyes may present |
Experiment No: 04: The sample is warmed in a dry test tube with chloroform or benzene.
| Observation | Inference | Remarks |
|---|---|---|
| No colored solution | Absence of naphthol color | Reactive dyes may present |
Experiment No: 05: The sample is treated with cold concentrated H2SO4 and diluted with water carefully sliding it into the test tube.
| Observation | Inference | Remarks |
|---|---|---|
| No Ring Formation | Absence of naphthol color | Reactive dye present confirm |
Result: 08: The dyed sample was found to be dyed with reactive dye.