Sunday, 29 May 2011

Indigo Dyeing using Fermentation Vat

Some Notes on Indigo Dyeing using Fermentation Vat

1. Indigo itself doesn not exist as such in nature. It is easily formed by oxidation of a a part of plant called IndigoFera by exposure to air. 

2. Simply speaking, Indigo itself is a blue solid. It is insoluble in water, acid and alkalies. If Hydrogen is added to it, or chemically speaking it is "reduced" by many reducing agents- It changes to "Indigo White" which is colorless. This indigo white can dissolve in water, in presence of alkalies, to a bright yellow liquid. When Textile substance is dipped in it and exposed to air, white indigo takes up oxygen and get converted into blue coloring matter. 

3. In fermentation method water is made alkaline with the the addition of Lime or Alkali. Then substances are added which can ferment easily in the presence of alkali, for example wheat bran (madder is added to expedite the fermentation). It takes about two to three days to ferment and then indigo is added. This bath can be used for several days or even weeks. Fresh indigo and other ingredients are added from time to time. The color of bath is light greenish yellow in color with a blue or bluish green scum. Goods immersed in this bath turns yellow. When they are taken out and exposed to air, the yellow color quickly changes to blue.

3. The color of the bath is very important. If it is bright yellow, it means too much alkalanity and more indigo should be added. If the color is too dark, it needs more lime or other alkali. 

4. After the color has changed, the goods should be rinsed well in two or three waters. After that should be boiled for several minutes in a soap bath to washoff the loose dyestuff and prevent rubbing. Rubbing can also be prevented by building up deep shades by successively dippings in the moderately weak vats, rather than obtaining the shade once for all. 

Here are some tips (Source)

1. Keep the vat covered. The level of water in the pot should be to the brim.

2. Wet out your fibers well. Any air remianing in the fiber will oxidise the indigo in the vat. 

3. Enter the fiber into the vat very carefully, to avoid any air in the wet. 

4. Always work under the vat. 

5. For greens, dye with indigo first. Then rise well and overdye with alum mordant and any yellow dye ( traditionally Turmeric). For purples, dye the Indigo first, rise well, mordant and dye with any red dye. 

Remember, you can use various chemicals to  reduce the indigo vat. The alkalnity of these chemicals vary from Soda Ash ( Sodium Carbonate), Slaked Lime ( Calcium Hydroxide), Sodium Hydrosulphide to Caustic Soda ( Sodium Hydroxide) in that order(from low to high). 


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Saturday, 28 May 2011

Some Notes on Denim Washing

There are four main processes in the Denim washing

- Pretreatment
- Stone or Enzyme Wash- To adjust the surface effect
- Bleaching- To adjust the color
- Finishing- To adjust the handfeel of the garment

Pretreatment involves removal of impurities from the garments and desizing the garment. It also involves prevention of creases in the garment. Wetting Dispersing agent is used in desizing process. It should be able to rapidly wet the jeans so that it can prevent white lines of creases and prevents back staining. Back staining is the redeposition of indigo dyed short fibers, or loose indigo, removed during desizing, stone-washing or enzyme washing. Backstaining reduces the contrast of warp and undyed weft. It also stains pockets and labels and it is more prone ot ozone and yellowing. An anticrease agent is added to prevent crease formation during the washing process. 

Enzyme in garment Industry

Enzyme is a kind of protein. They help the chemical reaction but themselves do not take part in chemical reaction. The starting molecule in a reation is called substrate and the yield molecule is called substate. Enzymes and substrate work like lock-key model so only one enzyme is useful for one type of substrate. Enzymes are better than chemical catalyst because they act in mild conditions such as room temperature. They are also biodegradable. Many enzymes are used in garment washing. An enzyme called Amylase is used in removing starch in desizing. Celullase is used in breaking and removing cellulose fibers. Laccase is used in biobleaching and catalase is used as an anti peroxide. 

Stone and Enzyme Wash

Cellulase weaken the surface fibers which are then mechanically torn off during processing, taking with them indigo. However, they need mechanical action to work. Hence they are used with stones. Cellulase is also used in biopoloshing, which removes surface fibers and make the surface smooth. 


Laccase enzyme decolorises indigo without using bleach. It provides very good contrast and since it attacks only indigo dye and not the fiber so it gives excellent tensile strength. 


The discolouration of textiles, i.e. a change of shade or loss of whiteness, giving a yellow tint, is commonly known as YELLOWING.Yellowing is due to many reasons. Cotton, yellows with age. However aging cannot make severe yellowing happen. Certain lubricants used in weaving and knitting can cause yellowing. The Anti oxidants present in these oils can cause a type of yellowing called as phenolic yellowing. The anti oxidants are also present in packaging materials and silicon softeners. Also temperature of drying and curing during processing can scorch the fibers and cause yellowing. 

Indigo dyed fabrics are more prone to yellowing. Indigo when exposed to NOx or Ozone can produce yellow colored compounds. Indigo itself through simple oxidation can transform into yellow colored compounds. 

There are specialised anti-yellowing softeners available. This work by either forming a protective filem, or by reacting the pollutants to form colorless compounds.

The source of these notes this presentation. This also contains images and chemical reactions. You can also view images of various denim washes here. One more resource is here.

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Saturday, 21 May 2011

Resources for Textile Technology Students

If you are a student of textile technology, you will find this site very useful. The owners of the sites are themselves textile students who have put together all the resources at one place.

While surfing I came across one more site, again very useful for textile students.

Please do not miss their blog.

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Some Selected Notes on Textiles: Part -5

Flammability Test

This is important for nightwear as they are finer and thinner than regular wear and are more prone to flammability than other fabrics.

In the testing, among other things time required for the flame to travel a certain distance is determined. It is now mandatory to have a flammability test if the fabric GSM is less than 88 grams.

Samples are tested both as submitted and after one cycle of washing and dry cleaning to obviate any instance of flammbility finish that might get washed of after one washing. Also iginition behaviour of the fabric is observed. Normally 5 specimens are tested. If they do not get ignited than 10 specimen are tested.

Butane gas of specified parameter is used. Based on the ignition behaviour, fabric is classified into Class I, class II and Class III. You can learn about the classification here.

You can read some facts about fabric flammability here.

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Tuesday, 17 May 2011

Some Selected Notes on Textiles- Part 4

- Colorfastness to Light: In this the samples is exposed to a light source along with blue wool sample. The fading is observed and the rating is given.  The main difference between American and European Standards is that American standard is time bound. In European standards it is not a time bound test but fading bound test- means you have to keep on exposing the sample till the sample fades to that of blue scale. Factors affecting lightfastness are the type of dyes used, depth of shade, surface structure and finishing chemicals. 

- A cotton pigment printed fabric cannot be dry cleaned . In dry cleaning solvent called Perc- Perchloro Ethylene or Tetrachloroethylene. Pigments are very susceptible to dry cleaning- they will come out. Perc is the only solvent that do not blast. In exports they use MTO . The problem with perc is that it damages Ozone layer. Perc will take out the pigments from the print. However, if you dry clean with MTO, nothing will happen.  Perc does not smell as much as MTO does.  To test for dry cleaing, a bag is prepared where instead of steel balls, stainless steel discs are added. 

- To remove smell from pigment printed fabric, it has to be cured well. To do it, maintain a temperature of 150 deg and allow the fabric for 10 minutes. It will cause phosphoric acid to get liberated and pigment get fixed- for that Diammonium phosphate needs to be added – so fixation takes place under acidic condition.  

- When testing for shrinkage, the fabric is conditioned for 24 hours. Then it is subjected to washing process for 45 minutes to 1 hours. Then it is dried and reconditiond before remeasuring.

- When testing for shrinkage, soft water is used. Alum can be used for softening. Just move the alum on the upper surface for a few times. Now decant the upper portion and use the rest of the water for testing. One can also use wetting agent. 

- Drying can be line drying, wet drying, tumble drying or drip drying. 

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Sunday, 15 May 2011

Some Selected Notes on Textiles- Part 3

- Color Fastness to Rubbing – There are two types of it, dry and wet. Dry rubbing is important for the materials like sofa covers where a person sits on it. Normally it is done using Croakometer with 10cm track length and 9.8 N force.

- For all colorfastness evaluation it is done either visually or using spectrophotometer. Normally worst rating is given.

- Colorfastness to water – It is done to measure colorfastness to water under intimate contact when getting wet, for example contact of inner wear to outer garments in rain. The sample is wet in distilled water , put between two acrylic sheets and then it is clamped under a force of 4.5 kg and put in incubator at 37 degrees Celsius for  4 hours.

- Colorfastness to Water is not the same as colorfastness to washing.  In measuring colorfastness to water we use distill water, whereas in colorfastness to washing, the detergent is used which makes the pH alkaline. A case is cited where a fabric had excellent colorfastness to washing but poor colorfastness to water. It can be due to the fact that the fabric was dyed with reactive dyes. There was some hydrolyzed dye present, but it had no reactivity and hence it was unable to react with water so there was no bleeding. On the other hand that hydrolyzed dye migrated in case of pressure and water hence had poor colorfastness to water.  Thus rigorous soaping could have solved the problem. Taking the other aspect, a fabric had poor colorfastness to washing but excellent colorfastness to water. It can be due to the fact the dye is probably sensitive to the pH.

- Colorfastness to Perspiration- Test is done similar to Colorfastness to water; the only difference is that a solution is prepared which simulate perspiration and the fabric is dipped in it, rest of the procedure is the same. Two types of solutions are prepared , one simulating alkaline perspiration with a pH of 8.0 and the other simulating acidic perspiration with a pH of 5.5. To prepare this solution Sodium Chloride and Lactic Acid are the main ingredients. The test conditions of 37+- 2 deg Celcius for four hours under a pressure of 5 kg. – Picture Source and Procedure

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Some Selected Notes on Textiles- Part 2

- Acid dyes are used for silks. There are three categories of acid dyes- Leveling or strong acid dyes, Milling or weak acid dyes and super milling or fast acid or neutral dyes. The colorfastness of fabric is decided by which of these dyes are used.

- Colorfastness to wet scrubbing is only for pigment printing. Pigment has no affinity to fiber yet it can be applied to all the fibers.  Here a brush is used to see the shade change. 

- Colorfastness to ozone is used only for Denim, which tends to turn yellow either due to atmospheric fumes or ozone. 

- REACH- Registration Evaluation Authorisation of Chemicals is a European document which enlists 800 chemicals which are carcinogenic. Out of which 56 chemicals are SVHC- substances of very high concern. Out of these 56, only 25 are related to textiles. 

- Presence of Alkyl Phenol Ethoxylate is a compound present in cheap detergents. 

- Colorfastness is the property of a color to retain its color under different conditions of use. 

- Colorfastness to washing is checked for many different fibers using a multifiber fabric. It is important to know the colorfastness against different fibers as we don’t know which all fibers will go together in a washing load. Please see Picture Source and Procedure here.

Washing Fastness Tester

- ISO grey scales are used. There are two types of shade cards- color staining and color change ( shade change).  Grey scales are used as opposed to colored scale because only intensity of color change is seen vis-a –vis intensity of grey scale. 

- Internationally a ½ point deviation is acceptable. Normally the evaluation should be done by minimum two people. This is done with D-65 light source for evaluation. 

- This scale is used  for all tests except light fastness ( For light fastness we use 8 scale- Blue wool scales are used)

- Cross staining is transfer of color from a darker to lighter component within the fabric. 

- A case is sited where there was a red dress with white piping. The red dress had a colorfastness of 4-5. But still it was enough to make the white piping pink which was not acceptable. For this case the minimum acceptable fastness was 5. 

- When measuring colorfastness to washing, the test replicates 5 typical home launderings. 

- The Load contains multi fiber test fabric, standard reference detergent, steel balls, washing devices and grade 3 water ( grade 1 is the purest). Addition of steel balls accelates the process. In testing silks steel balls are not used. 

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Saturday, 14 May 2011

Some Selected Notes on Textiles - Part 1

- Strength of Cotton is in between silk and wool. Silk is the strongest fiber.

-  Cotton is less elastic than Silk.

- Cotton wrinkles as the cellulose from which it is made has hydrogen bonds that break when washed due to agitation or mechanical action. They are formed again when ironed but in different places. Read more...

- Perspiration is of two types- Alkaline and acidic. Majority of the perspiration is alkaline. Cotton is not affected by alkaline perspiration whereas silk does.

- Coloration principle involves physical absorption of water soluble dyes, transferring of dye on to fiber, dye becoming water soluble and is retained inside the fiber.

- Reactive dyes physically react with fibers and form covalent bonds. The process involves two steps: 1. Dyeing with the dye in presence of salt to effect as exhaustion as possible ( transferring of dye from solution to fabric) and 2. Chemically reacting the dye with water in presence of alkali like soda ash.

- Reactive dyes also react with the water in which they are dissolved.  This is called hydrolysis of dyes. These hydrolysed dye has to be removed from the fiber by proper soaping else color fastness will be a major issue.

- Disadvantage of reactive dyes are that the hydrolysis accompanies fixation, as told earlier. Also there there is approximately 30% wastage of dye due to hydrolysis. Only 70% of the dye react with fiber.  To remove hydrolysed dyes there is an excessive consumption of water. Also colored effluent discharge is a major problem. It also involves large amount of electrolyte ( Common salt) as a exhaustive agent. It is also costlier. 

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Saturday, 7 May 2011

Toda Embroidery- A Tango of Needles

Toda Embroidery



Toda people have a unique way of dressing. Both men and women cover themselves with a unique shawl  called Puthukuli which is designed and embroidered by themselves. It is intricately embroidered with red and blue or black threads at the borders. It is worn like a Roman Toga.  On one end of the cloth three stripes- two of red and one of black are woven into it. It is in these stripes that the embroidery is worked.  The darning stitch is used for embroidering motifs and patterns.  The base fabric is  bleached white cotton with a balanced weave structure. It enables the artisan to count and embroider the pattern.  No embroidery  frame is used  but instead they use their fingers to see, count and pick up threads by stretching the fabric. At each turn little tufts of threads are left protruding body. This technique ensures that each pattern created has a rich texture.  Patterns used for embroidery are similar to the ones used for tattoo marks.

Sources of Images and Text



3.  A very nice story for children depicting Toda Culture




Wednesday, 4 May 2011

Chuna Patri Printing Process of Bagru

It is amazing to know the variety of printing processes used in traditional printing in India. One of them is Chuna Patri process used in Bagru.

In this process a solution is prepared using Patri( Aniline Hydrochloride), Potassium Chlorate and Copper sulphate. 

Potassium Chlorate
Aniline Hydrochloride( Patri)
Copper Sulphate

Fabric is dipped into it and while it is wet, it is printed with lime + Gum. Lime acts as a discharge and doesn't allow the black color to develop on those areas. 

Fabric Printed with Lime
It is then dried in the sun. Every part of the fabric which is not printed first turns green and then jet black upon exposure to sun.  

Fabric Turning Green on Exposure to Sun
Fabric Turning Black Gradually
The problem is that the Patri and Potash makes the fabric weaken so post washing is very important.  To get a grey, black color is added with lime. It gives some of the best Blacks and white you can ever find. 

The Dye class is aniline black, used by Century Textiles long ago for dyeing their umbrellas. Patri is Aniline Hydrochloride, also known as aniline salt. It is a product that is made by aniline oil and HCl. This is in the form of white flake crystals and used for making black color in textile printing. 

It works on the principle that when a salt of aniline in solution is exposed to the action of oxidizers, it yields a black dye of such depth that other dyes look grey or green in comparison. In this case the aniline salt dissolves in water to give a acidic solution with a pH of around 5. 

Cotton  is dipped in the solution containing aniline salt, potassium chlorate, which acts as an oxidizer and copper salt, which acts as an oxygen carrier. The dyed material them becomes greener due to formation of Emeraldine and then turns jet black. 

When a wet solution is then printed with lime, the Ca(OH)2 will neutralize the selected areas as well as bleach them by forming calcium chloride, which gives such a brilliant white color. 

Faults during Patri Printing

1. Unevenness: This is mainly due to uneven impregnation. It also occurs when the fabric is allowed to come in contact with water before it is turned black. Even wet hands will lead to unevenness. 

2. Greening: This is due to insufficient oxidation. Often this is observed after some storage. 

3. Rubbing: This is due to the improper dyeing conditions and chemicals. 

4. Bronziness: This is due to over oxidation.

5. Tendering: During the formation of black a considerable amount of free Hydrochloric Acid may be formed, which upon acting on the cellulose at the elevated temperature is likely to attack cotton and produce tendering by formation of hydrocellulose. It can also happen if the fabric is aged ( exposed to air) for a prolonged period before washing. It is suggested that Ammonium Chloride should be added in the liquor to prevent this tendering. 

Further Studies

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