Wednesday, 30 March 2011

The dreaded subject - Chemistry

When I started writing this blog post I soon realized that it would be very, very long – I have pondered long and hard about whether it should go here or I should try and get it “in print” – it’s not until you start writing that you realize just how complex it all is to explain!!! For this reason I have decided to split the whole thing up into several posts.


For many people indigo is magic but they are simply dyeing with it for the experience rather than wanting to take it further, a simple dye kit or 1 day workshop is great and will satisfy their requirement. For others indigo “bites” and becomes such an integral part of their dyeing repertoire that they really need to understand everything that is happening in the bath and how works. Sadly very few seem to! If you are a professional dyer and particularly if you are writing a book it feels criminal to me that you cannot explain properly how the colour blue is obtained. One of the biggest insults (and reason behind starting all this writing) is when I read (or hear someone say) that it is “normal” for indigo to rub off.

Nooooooooo!

So here I am keeping my promise! I said I would lay my own neck on the line and give what I understand to be the chemistry going on in the “indigo” bath.-

Perhaps I should say here that I have no chemical training further than I took chemistry to A level way back in 1974 and failed it (well got an O level pass, but I already had the O level so......) From then until I took up natural dyeing the only links to the subject that I had were with the nutrition and food poisoning I had to study for my catering qualification. What I am trying to say is that this is a layman’s version, not a chemists!

I would like to start with clarifying names. Everyone talks about dyeing with “Indigo” but that is incorrect, the ACTUAL name of the blue dye chemical is INDIGOTIN (I don’t care how you pronounce it, but that’s how it’s spelt!) So throughout this ramble that is the term I will use when I am talking about the blue dyestuff. ( I feel that we would all get less confused if this term was used more often!)

I am not intending writing here how I use the dye but my understanding of what is chemically happening from the point at which you pick leaves from your chosen source plant and end up with a blue colour on your textile.

When doing a period demonstration dyeing with woad I start by saying::

“There is no blue dye in the leaves,- there is a “precursor” chemical and a naturally occurring chlostridia bacteria in there and when you tear the leaves up into little bits you release the chemical and bacteria into an environment they find suitable for the process of change to begin”

So let’s go through the best known of the plant sources and their “precursors” To clarify what I mean by this - there are many plants which contain a chemical within the leaves that can be converted into indigotin, the plants come from different countries, they are from different family groups and they contain a different chemical but ultimately they can make the required conversion.( I should perhaps also say that different methods of preparation can also be employed for the different plants.)

The Isatis family - Woads

It has not long been known that there is an Isatis family! This is currently under research - there seem to be more varieties than previously thought!

Isatis tinctoria (Woad)

Occurs in a wild state throughout Europe but is thought to originate in Russia. It was not native to England but was cultivated there as it was in Germany and Central Europe. It also can be found in Africa and Asia.

Isatis Tinctoria L. Var. Yezoensis (Ohwi)

 Found in Korea, China and Japan growing wild on hillsides

Isatis Indigotica (Chinese Woad)

This plant has not been found in the wild, only as a cultivated plant.

There are 2 major precursors in Woads – isatan A and isatan B. Indican is also present, but in a very small quantity, so is only a minor precursor for this plant. isatan B and indican are both converted by the same enzymes however isatan A requires a different enzyme. There are other precursors also present but in much smaller quantities and they have yet to be named!

The indigofera family.

This is the most important and largest of indigotin producing families – it is also found in most parts of the world. There are approximately 700 species occurring in sub tropical conditions – so they can be found in the Americas, Asia and Africa. There are no native species in Europe or Australia The ones most commonly known are:

Indigofera tinctoria

 this is sometimes called Indian Indigo Its origins are not known, but are assumed to come from India, although it can be found as far away as South America and Australia

Indigofera .suffruticosa

 Found in Central and South America it has been cultivated in many tropical countries due to its high indican content.

Indigofera arrecta

 Sometimes called Natal Indigo it is native to Africa particularly tropical Africa often at higher altitudes.It was introduced into Java and India.

Indigofera coerulea

 Is found in Sub tropical Africa from Mali to Somalia, also found in Algeria through Arabia to India. This plant was cultivated in the drier area to which it is well suited.

The Indigofera plants all contain the colourless precursor chemical indican in the leaves. The indican content varies from species to species, in the age of the plant, the age of the leaves and even the time of year. For example there is more indican in the young leaves of an older plant that in the young leaves of a young plant, there can also be more in the top leaves of a plant than the bottom! The dye yield from Indigofera arrecta is higher than from any other of the Indigofera species.

Persicaria Tinctoria - Dyers Knotweed

Also known as Polygonum tinctorium it is a native of Vietnam and Southern China. It was introduced in to Japan in the 4th Century AD and became the main source of indigotin.

Again the precursor chemical found in this plants is indican

Around the world there are many more plants which contain precursor chemicals principally indican and they are used by natives of their country. For a more thorough breakdown of all the plants please refer to Natural Dyes by Dominique Cardon her book is by far the best breakdown of what is known at the present time of all the indigotin bearing plants (in my humble opinion!) .

Copyright © Debbie Bamford 25th March 2011

5 comments:

Knitsister said...

Golly, I am glad I don't have to remember all of this ;)

Marytheknit said...

Keep it coming, Debbie.

I was messing about with Indigo only this weekend. Besides a silk scarf (lovely result), I dyed a skein of wool, a sock blank (two strands knitted together) and a tube made on the circular machine, folded in half before it was tied. I didn't get quite the results I wanted on these, but learnt a few lessons.

Phiala said...

Fascinating stuff, isn't it? :)

You're obviously trying very hard to get it right, so I thought you might not mind some minor corrections.

Isatis is a genus in the Brassicaceae, the cabbage family. It isn't a family on its own - there's no woad family - but there is a tribe, Isatideae. A tribe is a group smaller than a family but larger than a genus. A species is the basic unit, and a genus is a group closely-related species.

Similarly, Indigofera is a genus in the Fabaceae, the bean family. Again, not a family itself, but part of a larger family, and of the Indigofereae tribe. (You can always tell which is which: families end in -aceae and tribes in just -eae.) Taxonomy within Fabaceae is rather complicated, but this is the generally accepted version.

You did a very nice job with the precursors and bacterial chemistry. Isn't the woad-Clostridium connection neat? (Clostridium is the genus; clostridia is the plural used to refer to several members of the group.)

I'm a dyer and professional botanist with a fair bit of taxonomy experience, and would be happy to talk about dye plants with you any time! :)

Debbie said...

Hi Phiala, thanks very much for the correction - much appreciated, it DOES matter to get it right! I'm currently at ISEND 2011 in La Rochelle and getting VERY frustrated with the "experts" who are not making the effort to get the terminology right at all!
The next stage will be the extraction process from the leaves of the various indigotin sources and then on to the chemistry!

Silvina said...

Hi! I´ve been dying with indigo last weekend and it´s wonderful!! thanks for sharing this information!