**6. Purification and characterization of natural dyes**

The aqueous extraction of the corresponding dye solution is double filtered in fine mesh nylon cloth and sintered glass crucible and the filtrate is evaporated using a vacuum oven at lower temperature (70°C) to a semi-dried solid mass and the same is then put in a cage of the wrapped filter paper and further subjected to extraction in soxhlet apparatus using 1:1 alcohol:toluene mixture for 10 cycles for 2h at 70ºC. The alcohol- toluene extract of the colour components is finally subjected to evaporation in a water bath at 50ºC to get a semi-dry mass of the pure colour components. Finally, this dry mass of the colour components is washed with 100% acetone followed by washing with methyl alcohol and final drying in air to obtain the dry powder of the pure colour components of the corresponding natural dyes.

For characterization, purified dye powder is to be taken for preparation of 1% aqueous dye solution separately and is subjected to wavelength scan in a micro processor or computer attached UV-Vis absorbance spectrophotometer for 190-1100 nm range. Further, individual purified natural dye powder is washed once again in distilled water and in 100% acetone in sequence before final drying and may be subjected to FTIR Spectroscopy study in double beam FTIR spectrophotometer using KBr disc technique for characterization of its chemical nature and functional group present in the natural dyes, which are responsible for solubilisation and mordanting power of natural dyes as well as its hypsochromic/bathochromic shift of the main hue.

For study of thermal behaviour by DSC (differential scanning calorimetry) study, individual purified natural dye powder is to be washed in distilled water followed by further washing in 100% acetone before final drying and then may be subjected to DSC or TGA (thermogravimetric analyser) study by standard method, for determining the different transition temperature of the purified dyes including temperature of degradation/dissociation. Thermal characterization by DSC/TGA is necessary for understanding the nature of thermal dissociation of natural dye component at different dyeing temperatures as well as application temperature.

#### **6.1 UV-Visible spectroscopic study**

UV-Vis spectral scan of aqueous/non-aqueous extract/solution of purified natural dyes having both UV-zone and visible zone (190-700 nm or higher) indicating peaks and troughs in different wave length shows its main hue, absorption etc. Peaks and troughs in visible zone thus indicate main colour and absorption. UV-Zone with/without peaks shows the property of the dye under UV-light, this may be correlated with fastness behaviour.

UV-Visible spectroscopic studies are carried out by different scientists (Erica et al, 1995) to identify the UV-Vis spectral scan of a number of natural dyes viz, madder, cochineal, indigo, etc., using different solvents for extraction. Neem bark (Mathur et al, 2003) colourant shows two absorption maxima at 275 and 374 nm while beet sugar shows three absorption bands at

Dyeing of Textiles with Natural Dyes 39

Detection of annatto dyestuff, norbixin and bixin is reported by means of derivative spectroscopy and high performance liquid chromatography (HPLC) (Bhattacharya, 1999). The sample preparation involved extraction with acetone in the presence of HCl and removal of water by evaporation with ethanol. This residue is dissolved in chloroform-acetic acid for derivative spectroscopy or with acetone for HPLC. Derivative spectra are recorded from 550-400nm. Analysis of cochineal colour in foods utilizing methylation with diazomethane is carried out emplying TLC and HPLC using a mobile phase of butanol/

**6.3 Test of toxicity, biotechnological processing and environmental impact of natural** 

Toxicity is the ability of a substance to cause damage to living tissue, impairment of nervous system or severe illness when ingested, inhaled or being absorbed by skin. The toxicity (Zippel, 2004; Joshi & Purwar, 2004) data provide evidence about the adverse effect of natural dyes to human body. The LD50 is the best-known figure for toxicity rating of any substance. It describes the 'lethal dose for 50% of the test animals' which is the amount of

Most of the natural dyes are found to be non-carcinogenic in nature. Moreover, natural dyes have positive effect on antifungal and anti bacterial growth. The crude methanolic extracts of stem and roots stem, leaves, fruit, seeds of artocarpus hetrophyllus (Khan et al, 2003) and their subsequent partitioning with petrol, dichloromethane, ethyl acetate and butanol fractions exhibit a broad spectrum of antibacterial activity. The butanol fractions of the root, bark and fruit are found to be the most active. None of the fraction is found to be active against the fungi tested. Mariegold (http://www.mdidea.com, 2005) shows negative test against microbiology control E-coli and salimonella. Chemo-preventative effects (Dwivedi & Ghazaleh, 1997; Dwivedi & Zhang, 1999; Benencia & Courreges, 1999) of red sandal wood oil are observed on skin papillomas in mice. Further, it is studied for red sandal wood's prevention of skin tumor development in CD1 mice and antiviral activity against herpes simplex virus-1 and 2. The hepatoprotective (Gilani & Janbaz, 1995) activity of an aqueous– methanol extract of rubia cardifolia (madder) is investigated against acetaminophen and CCL4-induced damage. Acetaminophen produced 100% mortality at a dose of 1 g/K in mice while pretreatment of animals with plant extract (natural dye source material) reduced the death rate to 30%. Test of acacia catechu (cutch), kerria lacca (lac), quercus infectoria (gallnut), rubia cordifolia (madder) and rumex maritimus (golden dock) against pathogens like escherichia coli, bacillus subtilis, klebsiella pneumoniae, proteus vulgaris and pseudomonas aeruginosa are also reported (Singh et al, 2005). Minimum inhibitory concentration is found to be varying from 5 to 40 µg. Using a bioassay-directed purification scheme, the active antibacterial principle from caesalpina sappan (sappan wood or red wood) is isolated and identified (Hong & Lee, 2004). The trypan blue dye exclusion test shows that brazilian lacks cytotoxicity against vero cells; it has potential to be developed into an antibiotic. It is reported (Bhattacharya et al, 2004) that arjun bark, babool bark and pomegranate rind are eco-safe, however sometime contains traces amount of red listed heavy chemicals in permissible limit. A critical and realistic evaluation of dyeing with vegetable dyes highlighting its metal toxicity of substances used in processing has been reported (Shenai, 2002) and it is mentionworty that mordanting with metal salt as pre-requisite for application of most of the natural dyes may contaminate the dyed textiles with objectionable heavy metals resulting carcinogenic

substance in kg/kg of body weight which kills half of the animals.

ethanol and 10% acetic acid.

**dyes** 

220, 280 and 530 nm as per recent study (Mathur et al, 2001). The visible spectra of ratanjot (Gulrajani et al, 1999) at acidic pH showed maximum absorption around 520-525 nm, but under alkaline pH there is a shift to 570 nm and another peak at 610-615 nm and red sandal wood shows a strong absorption peak at 288 nm , the maximum absorption at 504 and 474 nm at pH 10 in methanol solution (Gulrajani et al, 2003). Gomphrena globosa (Sankar & Vankar, 2005) flower colourant shows one major peak at 533 nm. The dye does not show much difference in the visible spectrum at pH 4 and 7. Absorption for dyes extracted from mimusops elengi and terminalia arjun are reported that depending on the concentrations of dyes in the dye-bath, the dye absorbtion on the fibre varies from 21.94 % to 27.46 % and 5.18 % to 10.78% respectively (Bhuyan et al, 2004). The colour components isolated from most of the barks contain flavonoid moiety. Extraction, spectroscopic and colouring potential studies of the dye in ginger rhizome (zingiber officinale) is studied and reported (Popoola et al, 1995) that the dye is soluble in hydroxyl organic solvents and gives one homogenous component of Rf value of 0.86 on chromatographic separation having wavelength of maximum absorption at 420 nm. Aqueous extract of different source natural dyes including red sandal wood, manjistha, tesu, cutch etc. have been characterized by UV-vis spectra to optimize the extraction conditions.

#### **6.2 Chromatographic analysis**

Thin layer chromatatography (TLC) is used by many workers to identify natural dyes in textiles (Kharbade et al, 1985). Dyes detected are insect dyes and vegetable dyes viz., yellow, red and blue colours. The natural scale insect, madder and indigoid dyes are also analysed by HPLC (Koren, 1994). TLC chromatography analysis (Guinot et al, 2006) is used to carry out a preliminary evalution of plants containing flavonoids (flavonols, flavones, flavanones, chalcones/ aurones, anthocynanins), hydroxycinnamic acids, tannins and anthraquinones, which are the phylo-compounds (colour compounds) found in the plants. Identification of dyes in historic textiles through chromatographic and spectrophotometric methods as well as by sensitive colour reactions is highlighted (Blanc et al, 2006) and further the retention of carminic acid, indigotin, corcetin, gambogic acid, alizarin flavanoid, anthraquinone and purpurin are also studied (Szostek et al, 2003). A non-destructive method is reported for identifying faded dyes on textiles fabrics through examination of their emission and excitation spectra. The quantitative and qualitative analysis of red dyes such as alizarin, purpurin, carminic acid etc. by HPLC are also investigated/analysed (Balankina et al, 2006). High Performance Liquid Chromatography (HPLC) has been also used by several workers to identify natural dyes.

The separation and identification of natural dyes is carried out from wool fibres using reverse phase HPLC with a C-18 column (Mc Govern et al, 1990). Two quaternary solvent systems and one binary solvent system are used to obtain chromatograms of dyes, isomers and minor products present in the sample. A linear gradient elution method has been applied to the HPLC analysis of plant and scale insect, red anthraquinonoid, mordant dyes, and molluscan blue, red purple and indigoid vat dyes (Koren, 1994). The method enables the use of the same elution programme for the determination of different chemical classes of dyes. In addition, it significantly shortens the retention time of natural anthraquinonoid dyes. Quantitative analysis of weld by HPLC shows that after a 15 min extraction in a methanol-water mixture, 0.45% luteolin, 0.36 % luteolin 7-glucoside and 0.23% luteolin-3'7 diglucoside are obtained (Cristea et al, 2003). HPLC analysis of indigo is reported (Son et al, 2007) and it is found that as the dyeing time is increased, structural changes of indigo component are attributed to decrease in colour strength of dyeing.

220, 280 and 530 nm as per recent study (Mathur et al, 2001). The visible spectra of ratanjot (Gulrajani et al, 1999) at acidic pH showed maximum absorption around 520-525 nm, but under alkaline pH there is a shift to 570 nm and another peak at 610-615 nm and red sandal wood shows a strong absorption peak at 288 nm , the maximum absorption at 504 and 474 nm at pH 10 in methanol solution (Gulrajani et al, 2003). Gomphrena globosa (Sankar & Vankar, 2005) flower colourant shows one major peak at 533 nm. The dye does not show much difference in the visible spectrum at pH 4 and 7. Absorption for dyes extracted from mimusops elengi and terminalia arjun are reported that depending on the concentrations of dyes in the dye-bath, the dye absorbtion on the fibre varies from 21.94 % to 27.46 % and 5.18 % to 10.78% respectively (Bhuyan et al, 2004). The colour components isolated from most of the barks contain flavonoid moiety. Extraction, spectroscopic and colouring potential studies of the dye in ginger rhizome (zingiber officinale) is studied and reported (Popoola et al, 1995) that the dye is soluble in hydroxyl organic solvents and gives one homogenous component of Rf value of 0.86 on chromatographic separation having wavelength of maximum absorption at 420 nm. Aqueous extract of different source natural dyes including red sandal wood, manjistha, tesu, cutch etc. have been characterized by UV-vis spectra to

Thin layer chromatatography (TLC) is used by many workers to identify natural dyes in textiles (Kharbade et al, 1985). Dyes detected are insect dyes and vegetable dyes viz., yellow, red and blue colours. The natural scale insect, madder and indigoid dyes are also analysed by HPLC (Koren, 1994). TLC chromatography analysis (Guinot et al, 2006) is used to carry out a preliminary evalution of plants containing flavonoids (flavonols, flavones, flavanones, chalcones/ aurones, anthocynanins), hydroxycinnamic acids, tannins and anthraquinones, which are the phylo-compounds (colour compounds) found in the plants. Identification of dyes in historic textiles through chromatographic and spectrophotometric methods as well as by sensitive colour reactions is highlighted (Blanc et al, 2006) and further the retention of carminic acid, indigotin, corcetin, gambogic acid, alizarin flavanoid, anthraquinone and purpurin are also studied (Szostek et al, 2003). A non-destructive method is reported for identifying faded dyes on textiles fabrics through examination of their emission and excitation spectra. The quantitative and qualitative analysis of red dyes such as alizarin, purpurin, carminic acid etc. by HPLC are also investigated/analysed (Balankina et al, 2006). High Performance Liquid Chromatography (HPLC) has been also used by several workers

The separation and identification of natural dyes is carried out from wool fibres using reverse phase HPLC with a C-18 column (Mc Govern et al, 1990). Two quaternary solvent systems and one binary solvent system are used to obtain chromatograms of dyes, isomers and minor products present in the sample. A linear gradient elution method has been applied to the HPLC analysis of plant and scale insect, red anthraquinonoid, mordant dyes, and molluscan blue, red purple and indigoid vat dyes (Koren, 1994). The method enables the use of the same elution programme for the determination of different chemical classes of dyes. In addition, it significantly shortens the retention time of natural anthraquinonoid dyes. Quantitative analysis of weld by HPLC shows that after a 15 min extraction in a methanol-water mixture, 0.45% luteolin, 0.36 % luteolin 7-glucoside and 0.23% luteolin-3'7 diglucoside are obtained (Cristea et al, 2003). HPLC analysis of indigo is reported (Son et al, 2007) and it is found that as the dyeing time is increased, structural changes of indigo

component are attributed to decrease in colour strength of dyeing.

optimize the extraction conditions.

**6.2 Chromatographic analysis** 

to identify natural dyes.

Detection of annatto dyestuff, norbixin and bixin is reported by means of derivative spectroscopy and high performance liquid chromatography (HPLC) (Bhattacharya, 1999). The sample preparation involved extraction with acetone in the presence of HCl and removal of water by evaporation with ethanol. This residue is dissolved in chloroform-acetic acid for derivative spectroscopy or with acetone for HPLC. Derivative spectra are recorded from 550-400nm. Analysis of cochineal colour in foods utilizing methylation with diazomethane is carried out emplying TLC and HPLC using a mobile phase of butanol/ ethanol and 10% acetic acid.

#### **6.3 Test of toxicity, biotechnological processing and environmental impact of natural dyes**

Toxicity is the ability of a substance to cause damage to living tissue, impairment of nervous system or severe illness when ingested, inhaled or being absorbed by skin. The toxicity (Zippel, 2004; Joshi & Purwar, 2004) data provide evidence about the adverse effect of natural dyes to human body. The LD50 is the best-known figure for toxicity rating of any substance. It describes the 'lethal dose for 50% of the test animals' which is the amount of substance in kg/kg of body weight which kills half of the animals.

Most of the natural dyes are found to be non-carcinogenic in nature. Moreover, natural dyes have positive effect on antifungal and anti bacterial growth. The crude methanolic extracts of stem and roots stem, leaves, fruit, seeds of artocarpus hetrophyllus (Khan et al, 2003) and their subsequent partitioning with petrol, dichloromethane, ethyl acetate and butanol fractions exhibit a broad spectrum of antibacterial activity. The butanol fractions of the root, bark and fruit are found to be the most active. None of the fraction is found to be active against the fungi tested. Mariegold (http://www.mdidea.com, 2005) shows negative test against microbiology control E-coli and salimonella. Chemo-preventative effects (Dwivedi & Ghazaleh, 1997; Dwivedi & Zhang, 1999; Benencia & Courreges, 1999) of red sandal wood oil are observed on skin papillomas in mice. Further, it is studied for red sandal wood's prevention of skin tumor development in CD1 mice and antiviral activity against herpes simplex virus-1 and 2. The hepatoprotective (Gilani & Janbaz, 1995) activity of an aqueous– methanol extract of rubia cardifolia (madder) is investigated against acetaminophen and CCL4-induced damage. Acetaminophen produced 100% mortality at a dose of 1 g/K in mice while pretreatment of animals with plant extract (natural dye source material) reduced the death rate to 30%. Test of acacia catechu (cutch), kerria lacca (lac), quercus infectoria (gallnut), rubia cordifolia (madder) and rumex maritimus (golden dock) against pathogens like escherichia coli, bacillus subtilis, klebsiella pneumoniae, proteus vulgaris and pseudomonas aeruginosa are also reported (Singh et al, 2005). Minimum inhibitory concentration is found to be varying from 5 to 40 µg. Using a bioassay-directed purification scheme, the active antibacterial principle from caesalpina sappan (sappan wood or red wood) is isolated and identified (Hong & Lee, 2004). The trypan blue dye exclusion test shows that brazilian lacks cytotoxicity against vero cells; it has potential to be developed into an antibiotic. It is reported (Bhattacharya et al, 2004) that arjun bark, babool bark and pomegranate rind are eco-safe, however sometime contains traces amount of red listed heavy chemicals in permissible limit. A critical and realistic evaluation of dyeing with vegetable dyes highlighting its metal toxicity of substances used in processing has been reported (Shenai, 2002) and it is mentionworty that mordanting with metal salt as pre-requisite for application of most of the natural dyes may contaminate the dyed textiles with objectionable heavy metals resulting carcinogenic

**7.2 Tannins** 

**7.3 Oils type mordants** 

a particular textile material.

2g/L industrial soap solution.

fastness and hue.

Dyeing of Textiles with Natural Dyes 41

The term 'tanning agent' is given initially to those water-soluble cellulosic materials that predicates gelatin from solution. But all gelatin precipitation did not identified as tanning agent. Tannins are polyphenolic compounds having capacity of gelling under certain conditions. (a) It may be hydroysable pyrogallol tannins exemplified by 'tannic acid', by Chinese or Turkish gallotannins (galls) and by Sicilain and Stagshorn sumac, (b) hydroysable ellagitannins that give ellagic acid or similar acids on hydrolysis, exemplified by valonea, chestnut, and (c) condensed or catechol tannins that contain little or no carbohydrates and are converted to acids to insoluble amorphous polymers. Among the

Vegetable oils or Turkey red oil (TRO) are such type of mordants. TRO as mordant is mainly used in the dyeing of deep red colour from madder. The main function of the TRO as oil mordant is to form a complex with alum when used as a main mordant. Sulphonated oil posses better binding-capacity than the natural oils. Oil mordanted samples exhibit superior

Mordanting can be achieved by pre-mordanting (before dyeing), simultaneously mordanting and dyeing or it may be a post mordanting system (after dyeing). Different types of mordants can be applied on the textile to increase the dye uptake of natural dyes. Extensive work has been reported (Paliwal, 2001; Jahan P & S, 2000; Sengupta, 2001; Prabu & Premraj, 2001; Sunita & Mahale, 2002; Moses, 2002; Rani & Singh, 2002; Bain et al, 2002; Paul et al, 2002) for dyeing of textiles with natural dyes adopting specific mordanting system for

In pre-mordanting method, the textile substrate is first treated in aqueous solution of mordant for optimized time (e.g. 30 - 60 minutes) and temperature (e.g. 70 – 100 °C) with a ML ratio of 1:5 to 1:20 and then dried with or without washing. The mordanted textile material is then dyed following optimized dyeing conditions may be required as salt, soda ash or acid depending on type of textile material and type of natural dye. After dyeing, the textile material is washed properly and soaping is carried out by 2 g/L industrial soap

For simultaneous mordanting and dyeing system, the textile substrate is immersed in a dye bath solution containing both mordant and dye in a definite quantity and dyeing may be started at the pre-determined optimum condition. Dyeing auxiliaries may be added as required for the standard dyeing process. However, for optimization of dyeing condition, dyeing process variables can be studied for specific fibre-mordant-natural dye system in order to maximize colour yield on textiles. After dyeing, the textile material is washed

In case of post-mordanting method of natural dyeing, the dyeing process is carried out for bleached textiles in the absence of mordant at pre-determined dyeing condition and the dyed fabric is treated in a separate bath called saturator containing suitable mordanting solution. Treatment condition may vary depending on type of fibre, dye and mordant system. After dyeing, the textile material is washed properly and soaping is carried out by

tannins, myrobalan (harda) and galls/sumach are most important.

**8. Different mordanting methods and application of natural dyes** 

solution as described in standard method of AATCC or ISO method.

properly and soaping is carried out by 2 g/L industrial soap solution.

effect. Therefore, selection of mordanting metal salt and its purity are important criteria to produce eco-friendly natural dyed textiles. Attempts (Mondhe & Rao, 1993a & 1993b) has been made to prepare azo-alkyd dyes by the reduction of nitro alkyds, followed by diazotization of aminoalkyds and coupling with different phenolic compounds present in jatropha curcas seed oil confirmed by using IR spectra.

### **7. Types of mordants**

Limitation on colour yield and poor fastness properties prompted a search for ideal mordants, the chemicals which increase natural dye uptake by textile fibres. Different types of mordants yield different colours even for the same natural dye. Therefore, final colour, their brilliance and colour fastness properties are not only dependant on the dye itself but are also determined by varying concentration and skillful manipulation of the mordants. Thus, a mordant is more important than the dye itself. Moreover, the ideal mordant for bulk use should produce appreciable colour yield in practicable dyeing conditions at low cost, without seriously affecting physical properties of fibre or fastness properties of the dyes. Also, It should not cause any noxious effect during processing and the dyed textile material should not have any carcinogenic effect during use. Mordants can be classified into the following categories:

#### **7.1 Metallic mordants**

They are generally metal salts of aluminium, chromium, iron, copper and tin. The metallic mordants are of two types.

#### **7.1.1 Brightening mordants**


#### **7.1.2 Dulling mordants**


#### **7.2 Tannins**

40 Natural Dyes

effect. Therefore, selection of mordanting metal salt and its purity are important criteria to produce eco-friendly natural dyed textiles. Attempts (Mondhe & Rao, 1993a & 1993b) has been made to prepare azo-alkyd dyes by the reduction of nitro alkyds, followed by diazotization of aminoalkyds and coupling with different phenolic compounds present in

Limitation on colour yield and poor fastness properties prompted a search for ideal mordants, the chemicals which increase natural dye uptake by textile fibres. Different types of mordants yield different colours even for the same natural dye. Therefore, final colour, their brilliance and colour fastness properties are not only dependant on the dye itself but are also determined by varying concentration and skillful manipulation of the mordants. Thus, a mordant is more important than the dye itself. Moreover, the ideal mordant for bulk use should produce appreciable colour yield in practicable dyeing conditions at low cost, without seriously affecting physical properties of fibre or fastness properties of the dyes. Also, It should not cause any noxious effect during processing and the dyed textile material should not have any carcinogenic effect during use. Mordants can be classified into the

They are generally metal salts of aluminium, chromium, iron, copper and tin. The metallic

i. **Alum:** Among all types of alum, potash alum is cheap, easily available and safe to use mordant. It usually produces pale versions of the prevailing dye colour in the plant. ii. **Chrome (potassium dichromate):** It is also referred to as red chromate. It is relatively more expensive. However, Cr3+ or Cr6+ is considered to be harmful for human skin as objectionable heavy metal beyond a certain limit of its presence. Its use has been limited as per the norms of the eco-standards. The dichromate solution is light sensitive

iii. **Tin (stannous chloride)**: It gives brighter colours than any other mordant. However, they are oxidized on exposure to air and may impart a stiff hand to the fabric. Stannous chloride also causes higher loss of fabric tenacity (tensile strength) if applied beyond a

i. **Copper (cupric sulphate):** Known as blue vitriol, it is readily soluble in water and easy to apply. It gives some special effects in shades, which otherwise cannot be obtained. However, copper beyond a certain limit is also under the eco-standard norms as

ii. **Iron (ferrous sulphate):** It is also known as green vitriol and is readily soluble in water. It is used for darkening /browning and blackening of the colours/ shades. It is easily available and one of the oldest mordants known. It is extensively used to get grey to

jatropha curcas seed oil confirmed by using IR spectra.

and therefore it changes colour under light exposure.

**7. Types of mordants** 

following categories:

**7.1 Metallic mordants** 

mordants are of two types.

**7.1.1 Brightening mordants** 

certain concentrations.

objectionable heavy metals.

**7.1.2 Dulling mordants** 

black shades.

The term 'tanning agent' is given initially to those water-soluble cellulosic materials that predicates gelatin from solution. But all gelatin precipitation did not identified as tanning agent. Tannins are polyphenolic compounds having capacity of gelling under certain conditions. (a) It may be hydroysable pyrogallol tannins exemplified by 'tannic acid', by Chinese or Turkish gallotannins (galls) and by Sicilain and Stagshorn sumac, (b) hydroysable ellagitannins that give ellagic acid or similar acids on hydrolysis, exemplified by valonea, chestnut, and (c) condensed or catechol tannins that contain little or no carbohydrates and are converted to acids to insoluble amorphous polymers. Among the tannins, myrobalan (harda) and galls/sumach are most important.

#### **7.3 Oils type mordants**

Vegetable oils or Turkey red oil (TRO) are such type of mordants. TRO as mordant is mainly used in the dyeing of deep red colour from madder. The main function of the TRO as oil mordant is to form a complex with alum when used as a main mordant. Sulphonated oil posses better binding-capacity than the natural oils. Oil mordanted samples exhibit superior fastness and hue.
