Persicaria tinctoria

Three strains of Japanese Indigo tested and observations on indigo extraction

An article by Ashley Walker
© copyright 2017

This year I had planned to carry out a tightly controlled experiment to look for variation in the amount of indigo produced by three fairly distinct strains of Japanese indigo. However due to a prolonged and still undiagnosed illness, my plans were thwarted and the experiment did not work out quite as I had hoped. However, on 12th and 13th October 2017, with help from Brian Bond another keen plant dyer, I did manage to complete a test of the three plants although the results are not directly comparable due to different planting times and maturity of each variety.

The strains

Round or wide leaf indigo

Persicaria tinctoria

Round or wide leaved Indigo. Directly sown bed

Grown from seed originally from the USA (from fellow natural dyer Pallas Hubler in Washington State on the west coast) who sent a few seeds over to Brian in 2013. We have been growing and saving seed from this strain ever since so it is possible that it has become adapted to growing in our soil.

  • Late flowering (October into November)
  • Pink Flowers
  • Compact short flower stems
  • Wide short or rounded leaves
  • Foliage pale to mid green
  • Easily damaged by high nitrogen levels in the soil. Grows poorly in cool overcast weather.

Long leaf indigo

Persicaria tinctoria

Long leafed Japanese Indigo in full flower.

Seed for this was obtained from the German supplier Rühlemann’s. Unfortunately this was in full flower by the time I was able to harvest it for the test and from previous experiments I know that once indigo has committed itself to flower production the amount of indigo in the leaf falls dramatically.

  • Large long pointed leaves
  • Pink flowers
  • Long delicate flower stalks
  • Early flower (September-October)
  • Dark green leaves
  • Very tolerant of high nitrogen in the soil and generally more robust.

An in-between white flowered strain

Persicaria tinctoria

Intermediate white flowered Japanese Indigo

The seed was obtained from Lisa George Fukuda a fellow plant dyer in Guernsey who had it originally from Teresinha Roberts at Wild Colours

Unfortunately this was planted out late in the year (August) so as yet I know little about its habit as there has not been enough time for it to grow to full maturity.

  • Longish leaves
  • White flower
  • Easily damaged by high nitrogen fertilizer.
  • Mid green leaves
  • Quickly bushes out, highly branching.

All three strains were grown on the Natures Rainbow allotment in Hitchin in a chalk soil with a strong application of Fish, Blood and Bone plus some chicken manure pellets.

Persicaria tinctoria

Leaves from all three strains.

Persecaria tinctoria

Rounded leaf Japanese Indigo growing with the Long Leaf strain in the greenhouse. Here they look like two completely different species.

The experiment

After stripping the leaves from the freshly cut indigo stalks, 220g of leaves from each strain were slowly heated from room temperature to 80°C in stainless steel pans with 4 litres of tap water. The pans were stirred at short intervals throughout. Note: the weight of leaves was determined by the amount of the long leaved strain that I could harvest from shoots that had not yet come into full flower as I wished to minimise the effect of flowering on indigo production. The amount of water in the pans was deliberately large as I wished the final colour to be on the pale side as variations in pale colours are easier to distinguish. More water also means the pot is easier to stir before the leaves are cooked.

Heating to 80°C took about 35 minutes. The pans were then taken off the heat and allowed to cool, free standing in the air for 1 hour. (The air temperature was appoximately 20°C).

Persicaria tinctoria

Intermediate Japanese Indigo extraction bath with container of liquor to show gray colour. Photo taken just after pan was removed from the heat.

At this point no difference could be noticed between the different pans. The liquor in each pan being a pale greyish blue in each case.

After one hour the leaves were removed by straining through an old pair of tights into a large plastic bucket. Half a cup of household ammonia was then added to the liquor. Taking care not to breathe in hot fumes, this liquor was poured back and forth from bucket to pan 10 to 15 times to aerate and oxidise the indigo precursor to indigo. The colour of the liquor changed from grey to yellow green, with the round leaved plant giving the darkest colour change and the long leaved plant the least. This is a good indicator of how much indigo is present in each pan.

Once oxidised to indigo, the liquor is now in a stable form and can be left for long periods without any loss of indigo. The reduction vats (indigo dye baths) were set up the following day as follows. The pans were heated to 50°C, one level teaspoon of Spectralite (Thiourea Dioxide) was added to each pan, gently stirred in and left for 30 minutes for the indigo to reduce to its soluble form. Identical weight skeins (26g) of wool were added to the baths at 50°C and left for 20 minutes before removal and oxidation in the air. The dye baths were kept in a hay box to maintain constant temperature during the dyeing.

The results

Japanese Indigo

First results showing a surprising difference in colour obtained

The long-leaved plants (left) were disappointing only producing an ice blue colour. The white-flowered intermediate-leaved plant gave a slightly deeper shade but still pale (centre). The round-leaved plant produced a respectable light blue (right).

The poor results for the long-leaved plants was understandable because of their flowering state, however I was surprised the colour was quite so pale. The good results for the round-leaved plant was a real surprise as I had become convinced these plants would not be the best. Overall the pale colours made me worry that I had not optimized the process and I decided to repeat the experiment for the round-leaved and intermediate-leaved white-flowered plants (I had no more of the long-leaved plant so I could not replicate this one).

On the second run I made one change which was to slow the cooling of the extraction bath after reaching 80°C by placing the pans in hay boxes. For this experiment, using 4 liters of water I was aware that this small amount of liquor would cool quickly, perhaps too quickly? An experiment we conducted some years ago revealed that premature cooling of the extraction bath resulted in a dramatic loss of indigo when processing woad leaves. Two years ago we discovered that leaving the bath at a high temperature for more than one hour also results in a loss of indigo so I have become wary of putting large baths in hay boxes which are capable of maintaining a high temperature for hours.

In this second run the results from the white-flowered intermediate-leaved plant improved but the round-leaved plant still produced the better result (which itself was no better than in the first run).

Skeins of wool dyed with Japanese Indigo

Second run with intermediate white flowered indigo plant compared to rounded leaf plant.

Skeins of wool dyed with Japanese Indigo

Comparison of intermediate white flower strains. The difference between quick and slow cooling of the extraction bath.

Wool dyed with Persicaria tinctoria

No real difference between runs for the Rounded leaf strain.

Discussion

In theory all three plants should have produced broadly similar amounts of indigo. That they did not could have been due to genetic differences but as noted above all three plants were at different stages of development having been planted at different times and the round-leaved strain had possibly adapted to the local soil over the 4/5 or so years I have been growing it. The poor results from the long-leaved plant may have been entirely due to their flowering state. The intermediate-leaved white-flowered strain had only been planted out in late August and may not have had sufficient exposure to the sun to develop much indigo.

The diversity of results shows how critical it is to grow and harvest the plant at the right time. I was certainly concerned that harvesting the plants in October was a risk, as all three varieties were producing flower buds (although only the long-leaved plants were in full flower). Later I extracted a concentrated bath of indigo by making up a large pan crammed full of leaves and only enough water to barely cover the leaves when they were pressed down forcibly. The results were pleasingly strong indicating that the leaves were still fully charged with indigo.

Skein on right dyed with a strong indigo dye bath

Skein on right dyed with a strong indigo dye bath

I will certainly be making strenuous efforts to continue to save the seed from the round leaf strain whatever the reasons for the underperformance of the other two strains!

Thanks to:

Brian Bond
Lisa George Fukuda
Pallas Hubler

Indigo dyed wool

The range of blues obtained from the three strains of Japanese indigo.