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

A return to the subject of Washfastness

Before Woolfest I was doing some washfastness testing of my yarns, I do these tests at random times and on random yarns so I get an idea of how good (or bad) the dyes I'm using are, and my standards of mordanting and dyeing of course.

My method is following the recommendations in Gill Dalby's book Natural dyes fast or fugitive (a very good book and one that I think doesn't get enough praise, it's small and reasonably priced and chock full of really sound information!) The tests are not totally scientific of course - I don't have access to full laboratories and testing equipment, but I make the best use of what I have.

The yarns are stitched into mordanted cotton parcels (I reckon that if there is colour leaching then the mordanted cotton will take up the dye and show staining more clearly than unmordanted) I use my washing machine on the whites wash cycle and a temperature of 60 degrees (not very environmentally friendly, but it is for a specific purpose and only at random times not every week or day) full spin and Bob's your uncle! The detergent I used for these samples was Amway SA8 colour, a powder detergent that I have used for many years, originally I bought it because it was great for septic tanks, it isn't actually organically certified, but is certainly more environment concious that most. I also have Ecover non Bio in the laundry room. I don't add fabric softeners in the laundry but I do always give my wools a final rinse of Eucalan when I've finished dyeing - it's a fabric conditioner and moth repellant and I like it lots!

This sample is wool, it's not the clearest of images and you can tell that the wool hasn't liked the boil wash but there is no transfer of colour at all onto the cotton, the threads on the right are originals and the felted blobs are the ones that have been washed. There is barely any difference in the colours between the originals and the blobs.

The dyes used here were indigo, persian berry and persian berry overdyed with indigo for the green, the yarn is my Welsh wool, it's a 2 ply yarn but knits up as a four ply and is fab for socks because it's so hardwearing (felts well too!!!)

The next samples were some linen yarns. The colour that you can see on the cotton is actually fibres that have rubbed off the linen, not colour transfer, not sure whether the photo is clear enough for you to make that out - but "in the flesh" it is obvious! Here the dyes used were madder, cochineal and logwood, again there is virtually no difference between the original colour and the washed. There are different thicknesses of thread some 8/2, 16/2 and 28/2. It's the 8/2 dyed with cochineal that has "rubbed" off onto the cotton, the others have a much higher twist to them, so I guess that's what's helped there.

I've given information about the detergents I use because it's another thing that can affect the dye colours - if I used one that was more alkaline I could find that the colours actually changed in the wash, the cochineals would go more purple for example, yet another thing to watch out for!

Holiday

I should already be in bed - have to get up at 4.45 to catch the ferry to Ireland- but didn't want to go without saying tara rwan!

I'll leave you with some photos of indigo dyeing I've been doing this week - I had a really good bath going and the colour is really rich!

On the far left is my Welsh sock wool, I've already hanked that into individual 50g's (it come in 500g hanks) then there's the embroidery wool - lovely and fine and finally some beautiful lace weight alpaca silk. I will have some of it at the Ravelry Day in Coventry next weekend.

Following on from an earlier post - having dyed the blues and then hanked up the Welsh I thought I'd better take a photo of my hand - just to see how much rub off there is - so here you are:

I can't say my hand is spotless, but I can say that the colour is ingrained, not just come off the hank! I always run the thread through my left hand whilst winding off - so that's 500g - there would be a stripe of blue across the fingers and palm if there had been any problems!

The method I use when dyeing indigotin blues is my own combination of various people's - principally J Liles and M Whipplinger, with a little help from Ethel Mairet. I make a concentrate and then make up the dyebath, I do lots of blue from 1 bath - keep it going all day and do blues first and then overdyeing afterwards (greens and purples). The main dyebath has probably been on the go for about 12 months and just gets topped up with concentrate as and when I feel it needs it. I can't bear to throw any away, so I even save drips and pour them back after I've finished for the day. I only ever use natural indigo - there is no synthetic in my house, I will sometimes make up a woad bath if there is a specific reason to do so, but generally I use indigo.

I'm now going to head for bed - I'll tell you what I think of cruising on the Shannon - Erne waterways when I get back!