Category Archives: Experiments

Shows Devil's Bit Scabious plant in early June with lush green leaves but not yet in flower. Inset is blue composite flower from previous year

Devil’s Bit Scabious as a source of indigo?

By Ashley Walker
Copyright 15th June 2019

Scan of page 62 of Traditional Scottish Dyes by Jean Fraser showing entry on Devil's Bit Scabious

Scan of page 62 of Traditional Scottish Dyes by Jean Fraser showing entry on Devil’s Bit Scabious.

Front cover illustration showing plant dyed yarns

Scan of original reference from Chemical Dictionary of Economic Plants aparently confirming that a blue dye can be obtained from this plant

Reference to Devil’s Bit Scabious from Chemical Dictionary of Economic Plants

Some years ago I came upon a reference to this bee-friendly and pretty blue flower being a potential source of blue dye in Jean Fraser’s book “Traditional Scottish Dyes and how to make them”. Jean attributed her information source to Ethel Mairet. In her 1916 “Book on Vegetable dyes” Ethel briefly mentioned that Devil’s Bit Scabious leaves, if treated like Woad, will give a blue colour but adds no further details. A quick internet search brought up a number of other references to this plant producing either a blue or green dye. Significantly an entry in “Chemical Dictionary of Economic Plants” (2001) edited by Jeffrey B. Harborne, and Herbert Baxter, states that fibres placed in an alkaline fermentation bath of the leaves will turn blue on exposure with the air, though the active chemical is not identified as indigo. Devil’s Bit Scabious (Succisa pratensis) a member of the honeysuckle family (Caprifoliaceae) and a related plant is Teasel (Dipsacus), which in turn is also mentioned as a source of blue dye – being apparently produced by dried flower heads.

At the time I was looking out for possible dye plants that had flowers that weren’t yellow, as this would make our dye garden a little more attractive to the eye. I am also a beekeeper and Devil’s Bit Scabious was being promoted as one of the most pollinator-friendly native flowers, so I set about obtaining some seed. I was disappointed however to find that although you can buy the seed it has very poor viability. My first attempt resulted in no germinations and the second attempt only produced 5 plants out of around 500 seeds. In the end I bought some plants from the Rosy Bee plant nursery and planted them in the dye garden where they have positively thrived. Finally (3 years later) I had enough plant material to try extracting the blue dye.

Method

Leaves of the Devil's Bit Scabious looking very much like Woad leaves

Basal leaves of Devil’s Bit Scabious which bear close resemblance in both size, colour and shape to Woad leaves.

All references to the extraction process say that the basal leaves should be used and that they should be treated just like Woad i.e. placed in an alkaline fermentation bath (possibly the urine bath). I was not happy about using urine, so instead opted for Jenny Dean’s recipe for hot extraction of indigo from Woad using ammonia as the alkali. In addition, I did a more conventional dye extraction by simmering the leaves for 1 hour and straining the liquor; then dyeing mordanted wool yarn in a heated dyebath with and without adding soda ash to raise the pH. Finally I set up a solar dyeing jar with leaves, wool yarn and some soda ash to make the liquid alkaline and set it aside in a warm place to ferment.

Results

Jenny Dean’s indigo from Woad extraction

After pouring boiling water over the leaves and leaving for an hour and straining, I obtained a pale yellow liquid.

Shows pale yellow colour of Devil's Bit Scabious liquid extract

Pale yellow liquid extract.

showing green liquid produced by adding ammonia

Adding the ammonia turned liquid a dark green.

 

 

 

 

 

 

shows colour change from dark green to orangy yellow after reducing agent added

Colour change after adding Thiourea Dioxide to the green liquid.

There was no sign of any free indigo nor the characteristic sherry colour from Woad. The next stage, adding the alkali and aerating was exciting because the liquid quickly went a lovely dark green, exactly as one might expect if there was indigo in there. I had my hopes up now for the first time! The next stage was to add a reducing agent and for speed I used a tiny amount of Thiox (Thiourea Dioxide). The colour of the liquid immediately changed to an orangey yellow – too fast for the normal indigo process.

Both samples of yarn shown are the same shade of white

Unmordanted raw wool yarn vs unmordanted dipped yarn. Left: raw wool; Right: dipped wool.

But I put in some un-mordanted wool yarn anyway and waited. I took the yarn out but obtained no discernible change in colour at all. Disappointment! I did several dips and left the yarn in for about 15 minutes, then did more dips, but sadly there was no colour change.

After drying, the wool does look slightly altered but it’s a bit of a stretch of the imagination to see any blue.

Later, I took some of the original green coloured liquid which had the alkali added and neutralized it with some distilled vinegar. The colour instantly changed back to yellow, indicating pretty conclusively that there was no indigo in it.

Color changes from green to orangy yellow when liquid is neutralised with white vinegar

lowering the pH of the green liquid with vinegar brings it back to an orange yellow.

Conventional extraction

Pale yellow alum mordanted wool top. Grey iron mordanted wool bottom

Mordanted wool yarn dyed in liquid extract before alkali was added.

Alum mordanted wool gave a pale straw yellow with no hint of green. Dyeing time ½hour.
Iron mordanted wool, unexpectedly, gave a rather nice slightly warm grey. Dyeing time 15mins.

Shows different colours obtained by mordanting the wool with alum, copper and iron

Colours obtained with three different mordants after leaving in alkaline Devil’s Bit Scabious dye bath over night.

After adding the soda ash, the liquid darkened off as expected to a greeny yellow though not as green as when using ammonia. Wool samples mordanted with alum, iron and copper were introduced and, after rinsing in clean water, produced a similar set of colours after about ½ an hour. At this point I decided to leave the samples in overnight. In the morning the alum mordanted sample was much the same but the iron mordanted sample had turned from grey to a warm brown. The copper mordanted wool was an attractive greenish bronze. Depth of colour had not increased during the night. Rinsing the yarn removed the green tint of the dye bath.

Discussion

The acute sensitivity to pH tells me that the chemicals producing the green colour in the alkali extract are not dyes and will not even attach to mordanted wool. The grey and light brown colours obtained with mordanted wool suggests that there are natural tannins in the leaves and also a yellow dye. The entry in the “Chemical Dictionary of Economic Plants” says the active dye chemical is a seco-iridoid glucoside. Internet searches suggest that these molecules protect the plant from predators and pathogens and are of interest for their anti-oxidant, anti-inflammatory and possible anti-cancer properties. I did find a reference to an iridoid called genipin which in a weak acid is reported to produce a soluble blue pigment in the presence of oxygen with potential as a food colourant. But to obtain this blue pigment seems to require a chemical laboratory! And there appears to be no logical chemical link to the indigo molecule.

I speculate that the mythical blue colour is one of those confusions that get passed from one source to another without anyone really testing it out. If by some miracle there is a blue dye to be had it is not indigo. Possibly someone at some point mistakenly put Woad leaves into a bath of Devil’s Bit Scabious, they are remarkably similar in shape and size. Or perhaps someone just assumed that since the blue/green was obtained in an alkaline bath identical to a Woad leaf extraction bath then they must be the same dyes.

Shows jar filled with leaves of Devil's Bit Scabious, water with a bit of soda ash added and wool yarn.

Hopefully this solar dye jar experiment is about as close as I can get to the original assertion that Devil’s Bit Scabious fermented in an alkaline liquid will give blue.

The results of the solar dye experiment will take some time. I think it is unlikely there will be any blue or green but we will see.

One further thought, there could be a bit of a pattern developing here, searching for a blue from Elecampane root (see blog post) I discovered a rather nice grey could be obtained. Here again I get another grey. Perhaps this is more evidence that the colour grey was often referred to as blue in earlier days.

Well, I’m keeping the Devil’s Bit Scabious in the Dye garden. It really is a fantastic pollinator-friendly plant and it looks good too.

References

Handbook on Natural Pigments in Food and Beverages – Industrial Applications for Improving Food Color. Edited by: Reinhold Carle and Ralf M. Schweiggert. 2016.

Jenny Dean’s Wild Colour. http://www.jennydean.co.uk/

Resources

Rosy Bee – Plants for bees.
http://www.rosybee.com/plants/devils-bit-scabious-succisa-pratensis

Persicaria tinctoria indigo extraction experiment

Hot vs Cold indigo extraction from fresh Japanese Indigo leaves

By Ashley Walker
Copyright 6th August 2018

Currently the main method of indigo extraction in use on internet Facebook pages is the 2 -3 day long soak in water. I believe this was the main method used commercially in the days before synthetic indigo wiped out the western market for natural indigo. Originally used to extract indigo from Indigofera tinctoria it is still used for small scale production in South Asia. The method is now used for Japanese indigo presumably because the traditional Japanese Method of composting the leaves is too large scale and time consuming for craft dyers. So it has been with some bafflement that I’ve seen the rise of this soaking method as I have always followed the Jenny Dean method which is even quicker.

We were introduced to plant dyeing through the pages of Jenny Dean’s “Wild Colour” and have used her recipe from this book for many years. It involves heating the leaves and can be done in two hours. Since we started to use this recipe we have tweaked it somewhat, discovering that there is no need to heat the leaves over 75 to 80°C to get maximum extraction. Another wrinkle is the need to allow the heated leaves to cool fairly rapidly. Large containers holding 20+ litres tend to cool too slowly and the indigo can be damaged. We did try one experiment when we cooled the extraction bath artificially but that was too quick and the results were very poor. An ideal extraction would be to heat about 1kg of leaves in 5 to 10 litres of water to 75°C and allow it to cool naturally over an hour. In our climate it will fall to around 40°C or less during that time.

So, now to the experiment which was a bit slap dash, but I am sure that it was systematic enough to have fairly good validity for a home dyer.

I picked just over 2kg of fresh Japanese Indigo of the Long Leaf variety which was showing no signs of any flower buds. This was divided into 2 lots of 1026g.

Persicaria tinctoria

Long Leaf Japanese Indigo showing leaf curl – a result of prolonged hot sunny weather.

Hot Soak Method (based on Jenny Dean)

Once batch of leaves was added to a large pan with about 8 litres of cold tap water (20°C) and then gradually heated with constant stirring to 75°C. This took exactly one hour and at the end the leaves had lost all of their fresh green tint and had turned almost black. The water was a very dark grey (a lot darker than usual in fact and I attribute this to a higher than normal amount of indigo in the leaf – a result of the weeks and weeks of hot sunny weather we have had this summer).

The leaves were then left to soak for one more hour, after which there was an indigo bloom at the surface and the water had darkened further. The leaves were removed (by straining through old tights) and 4 tablespoons of household ammonia were added with an immediate colour change to dark yellow/green. The liquid was then oxygenated by pouring from bucket to bucket about 20 times during which the liquid darkened to a green black. A small quantity of the liquid (viewed from above in a white plastic cup) looked olive green.

Indigo extraction from Japanese Indigo Hot and cold methods

Comparison of Hot and cold indigo extraction after 1 hour of soaking but before straining.

Cold Soak Method

The second batch of leaves was placed in a plastic bucket filled with about 8 litres of hot tap water (57°C). I used hot water because I did not wish to wait more than 24 hours. At this temperature the leaves become slightly cooked and release cell contents into the water quicker. The bucket was then set aside for 24 hours. After 1 hour the temperature had fallen to 44°C, the leaves were still quite green and the liquid was much paler and bluer than the hot extraction at the same stage. See image above.

After 24 hours the leaves were still greenish, although they had darkened somewhat. There was a lot of indigo scum on the top leaves. The liquid was grey with a blue tint. The plastic bucket was stained blue. Generally the results so far looked good, with much more blue visible than in the Jenny Dean method.

Indigo extraction from Persicaria tinctoria

Cold indigo extraction after 24 hours. Lots of indigo bloom on leaves.

Indigo extraction from Persicaria tinctoria

After leaves are removed, alkali (ammonia) added and liquid aerated.

Extraction of indigo from Persicaria tinctoria

Comparison of colour of water after extraction.

Leaves of Persicaria tinctoria after indigo extraction.

Colour of leaves after cold soak for 24 hours.

 

Indigo stained bucket

Empty plastic bucket used for 24 hour cold soak now stained with indigo.

The leaves were removed and about 4 tablespoons of household ammonia were added and the colour immediately changed to yellow green. The liquid was then oxygenated, by pouring back and forth between buckets about 20 times. During this process the liquid darkened until it was nearly black. A small quantity looked blue/green.

Dye test

Both extracts were then heated at the same time in separate pans to 50°C, the ideal temperature for dyeing wool, and spectralite reducing agent (thiourea dioxide, thiox) was added (one and a half teaspoons) to each pan. They were then left for about 2 hours to give ample time for the indigo to be reduced. The pots were then reheated to 50°C and an identical skein of wool (Corriedale) was added to each. Both pots were then gently stirred to promote even dyeing and the skeins were removed after 20 minutes.

Results

Initially the colour of the skein from the Jenny Dean (hot) method looked darker but on drying no difference could be detected.

Dye test. hot and Cold extracted indigo from Persicaria tinctoria

Test dye showing relative strengths of dye bath from Hot and Cold extracted indigo.

Conclusions

The amount of indigo extracted appears to be the same for both methods. However, heating, cooking and stirring the leaves increased the amount of fine particulate plant material in the liquid which increased the amount of sludge in the bottom of the dye bath.

I should clarify I don’t use lime (as a combined alkali and flocculating agent) to obtain a dried indigo pigment from my dyeplants. Any indigo I don’t use straightaway for dyeing, I store as liquid sludges. But I can see that for people who do use lime, the cold soak is advantageous because the resulting indigo pigment would contain fewer impurities than the hot soak because the liquid extract after straining is purer. For myself I’m quite happy to continue using my modified Jenny Dean process as it is fast and reliable.

Postscript

Out of interest I also decided to compare the Long Leaf Japanese Indigo to Woad. I processed a similar quantity of Woad leaf according to the 24 hour soak method in the experiment. Another wool skein was dyed in nearly identical conditions and the results prove to me that Woad can actually produce more indigo than Long Leaf Japanese Indigo.

Wool dyed with indigo extracted from Persicaria tinctoria and Isatis tinctoria

Comparison of strength of indigo extracted from Long Leaf  Japanese Indigo and Woad.

A note on alkalis

There has been a lot of controversy about which alkalis produce the best results. I have tried most of them and found that what is important is the pH not the exact chemical used to get there. Washing soda is the weakest and produces very poor results. Household ammonia is excellent and relatively safe, provided you don’t get it on your skin or breathe it in. Calcium hydroxide (lime) is good and has the added benefit of soaking up the indigo precipitate and settling it to the bottom fast (flocculation). Sodium hydroxide is also good but is very corrosive – a danger to skin and textile.
Whenever using strong alkalis you must take safety precautions: wear gloves; avoid splashes; don’t ever add water to dry alkaline powders or granules, add the powder to water; label colourless solutions and store safely; never leave sodium hydroxide solutions unattended for curious animals or children to explore (it is colourless and odourless and very corrosive indeed).

References

Wild Colour by Jenny Dean