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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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

1. http://www.cohands.in/handmadepages/pdf/331.pdf

2. http://www.parikramaholidays.com/pdf/Poothukuly-A-Toda-Ceremonial-Shawl.pdf

3.  A very nice story for children depicting Toda Culture http://www.arvindguptatoys.com/arvindgupta/22nbt-%20The%20Toda%20&%20The%20Tahr%20by%20E.R.C.%20Davidar.pdf

 

 

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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