When I joined the University in 1975, I already had a personal interest in producing natural textile dyestuffs from plants with the distant, castle-in-the-air dream that one day we might be able to grow crop plants to produce these wonderful natural colours on a larger scale for everyone to enjoy.  At that time, there was already a growing consumer interest for natural products in a world dominated by synthetic substitutes.

I immediately went boldly along to the Long Ashton Research Station (LARS) and was rewarded with an interview with the Director.  I said I wanted to set up a research project to find out how to grow woad (Isatis tinctoria) to produce indigo on an agricultural scale.  Would they be interested in helping me?  Well, some questions followed and, as you can imagine, the response was friendly and polite but... However, I was allowed to have a small patch of a few square yards for two years to run a trial of about 50 different strains of woad which I had collected together from botanic gardens around the world.

Indigo producing plants do not actually contain indigo but the leaves of these plants before they flower contain a substance which, when extracted from the leaf, forms indigo by absorbing oxygen from the air.  Indigo is notoriously insoluble in nearly all commonly used solvents, and especially in water, so the indigo formed in the extracts settles out as a precipitate quite easily.

I identified a few strains that gave the best yield of leaves for processing 

My first trial was harvested in 1976 (quite a problem with the drought!).  I identified a few strains that gave the best yield of leaves for processing to get the dye and the best dye content.  One of these was an exotic species of woad ("Tein-ching" Isatis indigotica) originally from China and unknown to most people in Europe, which has continued to figure in our research ever since. 

But I could not do more without funding - who would take this seriously, let alone fund such unlikely off-beam research?  And was this the sort of research a prestigious University like Bristol would like to encourage?

Years later in 1988, I applied to the Crafts Council in London for a research grant to see if we could produce natural dyes in the UK for the craft industry and was by unbelievable luck successful!  This paid for more trials at LARS but with Japanese "Ai" (dyers knotgrass Polygonum tinctorium) which can produce more indigo than woad - as I'd found out on my allotment and in my garden - and madder (Rubia tinctorum) that wonderful goose-grass-like plant whose roots produce the famous alizarin dye which dyes cloth red. 

However, I hadn't grown either of these plants in anything other than small quantities before.  Unsure of what my colleagues in the University might think of what I was doing, I analysed the indigo production of the Japanese "Ai" plants experimentally in my garden shed with Bolognese sauce jars, filter funnels from Boots and milk bottles rather than requesting laboratory facilities in the Botany Department.

Two of my main findings were that different strains of woad vary enormously in the amount of indigo they could produce and that nitrogen fertiliser could double the yield of indigo.  The results of these trials together with the earlier LARS trials with different strains of woad and some undergraduate honours projects (supervised in my previous job in the University of Newcastle-upon-Tyne) were written up in a paper on the possibilities of producing natural indigo in the UK and presented at a conference on woad (mainly on its history) at Erfurt in Germany in 1992. 

We were able to set up field trials and build a pilot industrial scale extraction plant

Also attending the conference was Dr Ulla Eggers of Livos Pflanzenchemie, a company based near Hamburg that specialises in natural products from plants.  We met and talked about the research and later that year she asked me to attend, as a "collaborating nation", a meeting at Livos to plan an application with scientists from the Agricultural Institute of Thüringia in Jena, Germany (Thüringia was one of the most important mediaeval woad growing regions in Europe) to the EC which had allocated about £2m of funding for research that included natural dyes. 

This resulted in a £250,000, three-year grant for Bristol, starting in 1993, which enabled two researchers,  Kerry Gilbert and David Cooke, to do some serious research on natural dyes.  The results were very positive on the feasibility of growing several crops on an agricultural scale, including woad for producing natural indigo.  We were able to set up field trials with different strains and dye-producing plants and build a pilot industrial scale extraction plant to obtain the indigo from the freshly harvested woad leaves. 

This project was followed by a further three-year grant from MAFF to find natural inkjet inks from plants for industrial printing jointly with Willett International, a multinational company.  This company was interested in having a range of environmentally friendly inks that could be used for downstream printing on packaging or even products themselves for such information as "sell by" dates.  We showed we could produce the colours needed (red, yellow and blue) although, in the end, the company did not pursue the idea all the way to the market place.   

An agricultural blueprint for farmers on how to grow the crop was written

In the meantime we had to look around for further funding to keep the work going. Kerry and I attended a conference on natural dyes in Toulouse and met Professor Philip John from Reading University who had been doing some interesting microbiological research on the mediaeval fermentation vat used in a re-enactment at Chiltern Open-Air Museum by John Edmonds.  They described a new species of Clostridium bacterium (C. isatidis) which was responsible for chemically reducing indigo in fermentation dyeing vats, based on a mediaeval recipe.

Joining forces with Philip John, we went back to EC funding with our former partner, the Agricultural Institute of Thüringia, and those in this country who had come on board with the ink project for a much larger project entitled SPINDIGO (Sustainable Production of Plant-derived Indigo) which involved a total of ten partners across five countries. 

We used a combination of agricultural trials, molecular and biochemical methods to identify the best strains, growing conditions and extraction methods.

The 3.6m Euros project was aimed at producing natural indigo to meet the European commercial market which would potentially mean up to 20,000 hectares of woad being grown across Europe.  We used a combination of agricultural trials, molecular (DNA) and biochemical methods in the laboratory to identify the best strains, growing conditions and extraction methods.  The results were very encouraging and in trials in Italy, Spain and the UK yield increased greatly and was found to be large enough to make the crop an economically viable proposition.

As a result of the EC project, an agricultural blueprint for farmers on how to grow the crop was written, machinery for extraction has been developed and an environmental impact statement for woad as a new crop has been written as part of Bristol University's contribution.  This is the first environmental impact assessment done for any new crop in agriculture in Europe.  It was praised by English Nature for setting standards for how novel crops should be assessed  

On 18 June 2004, a fashion show at Livos exhibited clothes dyed with SPINDIGO indigo - and so the dream that began with collecting seeds of different strains of woad in 1975 became a reality - via the garden shed - nearly 30 years later. 

One of our UK-based, EC project partners, Ian Howard, a commercial farmer, was so impressed by the results that he grew a substantial acreage of woad last year after the project finished and he has increased the area this year.

It now remains for the wider world to put production of natural indigo on a large scale - we have done all we can.

For further information, please contact D. J. Hill in the School of Biological Sciences.