Indigo: Sources, processes and possibilities for bioregional blue

Nicholas Wenner and Matthew Forkin June 2017 Photo by Kalie Cassel-Feiss by Kalie Photo Table of Contents

Introduction ...... 3

Indigo ...... 4

The Indigo Process...... 11

Conclusions...... 15 Photo by Paige Green Green by Paige Photo

Indigo Overview 2 Introduction

his report was completed with funding generously provided by the Jena and Michael King TFoundation as part of Fibershed’s True Blue project . It is one project of many that support Fibershed’s larger mission:

“Fibershed develops regional and regenerative fiber systems on behalf of independent working producers, by expanding opportunities to implement carbon farming, forming catalytic foundations to rebuild regional manufacturing, and through connecting end-users to farms and ranches through public education.”

In this report we present the various sources of blue dye and of indigo, and motivate the use of plant-based indigo in particular . We also identify the limitations of natural dyes like indigo and the need for larger cultural and systemic shifts .

The ideal indigo dye production system would be a closed-loop system that moves from soil to dye to textiles and back to soil . The indigo process has three basic steps: planting, harvesting, and dye extraction . In this document, we provide an overview of each, and detailed explorations are given in two separate documents that will be available through Fibershed by late-summer 2017 .

This report is based on a literature review of academic research, natural dye books, online content, and personal interviews . It benefited greatly from conversations with (and the generosity of) many skilled artisans and natural dyers, including Rowland Ricketts, Jane Palmer, and Kori Hargreaves .

Indigo Overview 3 Indigo

yeing is a major component of Dthe bioregional textile systems Fibershed aims to support . In the standard industrial processes, this step is also one of the most polluting . According to the World Bank, 17-20% of industrial water pollution comes from textile dyeing and treatment . Seventy- two toxic chemicals in our water come solely from textile dyeing, of which 30 cannot be removed 1.

Blue dyes have a long and rich history, and blue represents one of the most striking and challenging colors available from nature’s palette . Humans have used indigo in particular for thousands of years and throughout the A 6,000-year old indigo dyed cotton textile from Peru2 world . In fact, 6000-year old cotton textiles were recently discovered in a coastal area of Peru that were dyed in indigo, and these represent perhaps the and technical 5. Palmer worked with water, whereas the other natural dyes oldest known examples of cloth dyeing natural dyes in a production setting for showed inconsistency with the varied in the world 2. about 15 years, and—while she loves water sources and qualities coming into natural dyes in general—most posed the dyehouse on a given day . Palmer Indigo has low mammalian toxicity and huge challenges from a commercial turned to indigo dye partly because there is no indication of sensitization perspective, often fading quickly and she felt she was wasting so much water in humans after repeated skin having poor light- and wash-fastness tuning the other dyes . It was fortunate 3 applications . In fact, there are long and showing great inconsistency that public regard for indigo dye was histories of humans using indigo to color between batches . high, and economic and technical their skin and bodies . In ancient Britain, pressures pushed in the same direction . for example, the indigenous tribes were It was indigo alone that demonstrated known for painting their bodies and advantages in performance, economics, For its rich history, cultural faces with indigo pigment (from the and processing . Among the natural significance, beauty, low toxicity, woad plant) before battle 4. dyes, indigo is notable for high wash performance, practicality, and the and light-resistance . Unlike most other opportunity to reimagine a highly Not only does indigo offer a striking natural dyes, indigo can be used without polluting industry, natural indigo and non-toxic color, it is one of the most mordants to fix the dye to textile fibers . presents a great opportunity, and practical and durable of natural dyes . Without a mordant bath, Palmer supporting a local industry is a Jane Palmer of Noon Dye House in Los needed less equipment and was able to compelling goal for Fibershed and Angeles, CA turned from using a range use significantly less chemical inputs, those who share its values . of natural dyes to exclusively indigo for water, and energy . Indigo was also less motivations that were both economic susceptible to variations in incoming

1 Kant, R . (2012) “Textile dyeing industry an environmental hazard” 2 Los Angeles Times (2017) “6,000-year-old fabric reveals Peruvians were dyeing textiles with indigo long before Egyptians” 3 Vuorema, A . (2008) “Reduction and Analysis Methods of Indigo” 4 Finlay, V . (2012) “Color: A Natural History of the Palette” 5 Personal conversation

Indigo Overview 4 Sources of blue There are ongoing projects of The annual world production of indigo innovation in the dyeing industry, dye was about 80,000 tonnes in 2010 7. While there are multiple modern including non-indigo blue pigments Worldwide production of denim, the methods of achieving blue colors from natural microbial sources (from fabric from which jeans are made, uses in textiles—most notably fiber- groups like France’s Pili bio). as well as more than 95% of that production 8. reactive dyes such as those based on developments in structural color, which dichlorotriazine (e g. . Procion MX) or takes advantage of nanostructured While indigo was originally produced anthraquinone (e g. . Remazol Blue R)— surfaces to scatter light and produce from natural sources, there are now natural indigo is the only widely used color (as can be seen in the colorful multiple methods to generate the blue dye that both is non-toxic and can feathers of a peacock) . While these molecule, all of which can and have be produced from renewable resources . developments are certainly promising, been used for dye production . none are market-ready, and natural Unlike fiber-reactive dyes, both natural There are three general approaches to indigo remains the most viable and safe and synthetic indigo function by producing indigo: natural plant-based method available . adhering only to the surface of textile methods, synthetic petroleum-based fibers . The pigment can rub off of the methods, and newer microbial-based fibers (known as “crocking”) . While Sources of indigo methods using genetically-modified this could be seen as a downside, it is Indigo accounts for roughly 3% of all microorganisms . also the property that contributes to the dyes used globally today and about 15% favorable appearance of faded denim of the dyes used for cotton in particular 6. and is seen as a desirable feature for many textile products .

CHEMISTRY OF INDIGO EXTRACTION The chemical precursor to indigo in plants is indican, a glycoside . It exists throughout the plant but is concentrated almost exclusively in the vacuoles of the leaves 9. Although indican concentration can reach Indican as much as a few percent of the wet weight of the leaves, we still do not fully understand its biological function for the plant .

The extraction and subsequent hydrolysis of indican (achieved through heat and/or fermentation in water) cleaves the indican into Indoxyl two parts, resulting in b-D-glucose and indoxyl . The hydrolysis is achieved via enzymes naturally present in the leaves as well as by the b actions of microbes that likely seek the -D-glucose as food . Indigotin The interaction of indoxyl with a mild oxidizing agent (such as atmospheric oxygen) under conditions of high pH yields the blue pigment indigotin (the active pigment in indigo dye) .

Indigotin is only one of many oxidation products of indoxyl . Under non-ideal conditions, others—such as isatin and indirubin—can be Isatin formed, contributing to lower purity dyestuffs with lower quantities of the desired indigotin pigment 10. Indirubin

6 Ghaly, A . et al . (2014) “Production, Characterization and Treatment of Textile Effluents: A Critical Review” 7 Franssen, M . et al . (2010) “Industrial Biotechnology in the chemical and Pharmaceutical Industries” 8 Wolf, L . (2011) “Blue Jeans: Making the iconic pants requires both color-addition and color-removal chemistry” 9 Minami, Y . et al . (2000) “Tissue and Intracellular Localization of Indican and the Purification and Characterization of Indican Synthase from Indigo Plants” 10 Vuorema, A . (2008) “Reduction and Analysis Methods of Indigo”

Indigo Overview 5 PLANT-BASED INDIGO content . Powdered and granule forms ultimate environmental impact of the Plant-based methods involve the tend to be most readily available at 94- technology . For such an analysis, the extraction and processing of naturally- 100% purity . significant land and resources required occurring indican in plants and include to grow and process sugar feedstocks The price of synthetic indigo ranges the sukumo process and the water would need to be taken into account . from about $2/lb to $5/lb . The majority extraction process, which are discussed is produced in China, with other The technology of microbially- later on . suppliers in Europe and other parts produced indigo is not new, and its Currently natural indigo pigment of Asia . A full 40% of the market is story demonstrates that the synthetic represents less than one percent of controlled by BASF, with other major indigo industry is a force to be reckoned the indigo dye produced and used players including Japan’s Mitsui with . In the early 2000s, Bay Area worldwide . The main uses are as and England’s Imperial Chemical biotechnology company Genencor 13 colorant for beauty products like Industries . partnered with Levi’s to produce hair dye and for designer denim 400,000 yards of microbial indigo-dyed MICROBIAL INDIGO and artisanal textile products . It is fabric at near-market rates . Despite commonly available at purities of 20- Microbial methods involve inserting this success, the technology never took 50% at a price of $20-70/lb . Production the genes for indican production from off, as Levi’s synthetic indigo producer is concentrated in Asia, and some US plants into microorganisms that can in China promptly slashed prices and 16 domestic production is underway— then be cultured and concentrated . The pushed Genencor out of the market . most notably through Stony Creek process has been employed at the lab There are possibilities for directly Colors in Tennessee, who currently scale for decades . One recent method dyeing textiles with indoxyl, a precursor contracts with 16 farmers to cultivate is that developed by Professor John to indigo in the water extraction about 180 acres of indigo 11. For sukumo, Dueber and his lab at UC Berkeley . process . In fact, home-dyers may be production centers in Japan, where Using sugar feedstocks and genetically- familiar with this process as “green leaf production reached about sixty tons per modified E . coli, the Dueber Lab grows dyeing”, a process in which green leaves year between 1985 and 2009 12. cultures that can produce significant quantities of indigo . Dueber reports are blended and used immediately to SYNTHETIC INDIGO indigo production from his cultures of dye textiles a light blue . As the Dueber Lab has demonstrated, it is possible Synthetic methods include the 4. g/L and claims that production of 4 to achieve dark blue colors with this Heumann method (developed in 1897) g/L is easily imaginable in an optimized 14 process using either plant-sourced and the Pfleger method (developed process . or microbially-sourced indican 17. in 1901), as well as other methods As one point of comparison, trials in The process allows for in-situ indigo developed more recently . All of these Central Italy in 2001 and 2002 showed formation on textiles, bypassing synthetic methods use crude oil as a potential indigo pigment yields for the additives required to separately feedstock and employ a long series Polygonum tinctorium of up to 291 lbs/ precipitate indigo in dye production of sophisticated petrochemical acre 15. This 291 lbs of indigo would take only to later re-dissolve it in the techniques . approximately 13,200 or 132,000 liters dyebath . Indoxyl, however, is much less Synthetic indigo is available in powder, of Dueber’s liquid culture to produce— stable than indigo, and until a process granule, or liquid (solution) form . a liquid volume equivalent to that of a for controlling and sustaining indoxyl Liquid solution tends to be most readily cube about 8 or 16 feet to a side . in solution is developed, the process 18 available in 20%, 30%, and 40% pigment cannot be employed at scale . It is unclear at this time how the full life-cycle of microbial indigo affects the

11 https://www . racked . com/2017/6/16/15792068/stony-creek-colors-natural-dye-indigo 12 Kawahito, M . (2009) “Characteristics of Color Produced by Awa Natural Indigo and Synthetic Indigo” 13 https://www . bloomberg . com/news/articles/1997-03-30/a-gene-to-make-greener-blue-jeans 14 Personal communication 15 Angelini, L . et al . (2004) “Environmental factors affecting productivity, indican content, and indigo yield in Polygonum tinctorium Ait ,. a subtropical crop grown under temperate conditions” 16 Personal conversation with Professor John Dueber 17 http://2013 . igem . org/Team:Berkeley 18 Personal conversation with Professor John Dueber

Indigo Overview 6 Why plant-based indigo? While no study has fully characterized health and soil carbon sequestration, the human and environmental and no dangerous chemicals or Nearly all indigo in production today consequences of synthetic indigo processes are required . Even the waste- comes not from renewable resources, production, an understanding of the products can be employed beneficially: but as a product of the petrochemical process certainly raises concern . For After the pigment has been extracted, industry, with concomitant example, one of the many intermediate the plant residue can be composted and toxicological and environmental products in the process above is aniline, used as a fertilizer and the remaining concerns . a chemical that is toxic if ingested, water can be reused to irrigate crops . In general, the synthetic processes of inhaled, or touched that inhibits the indigo production are complex, far- ability of blood to carry oxygen and is reaching, and difficult to track . See fatal in high exposures . the image below for an overview of In contrast, natural indigo can be grown the Pfleger method, one of the major in an entirely sustainable manner . It methods currently employed . can be grown in a way that promotes soil

Graphic by Nick Wenner19

19 Information and images from https://www w. ikipedia o. rg/

Indigo Overview 7 Sources of plant-based indigo There are many plant sources for indigo, including India’s Indigofera tinctoria, Central America’s Indigofera suffruticosa, and the woad plant, Isatis tinctoria, used extensively in Europe .

Indigofera tinctoria20

Woad, Isatis tinctoria 21

20 https://www d. enimhunters c. om/how-denim-is-made-indigo-dyeing/ 21 https://en w. ikipedia o. rg/wiki/Isatis_tinctoria

Indigo Overview 8 The temperate United States is best suited for a plant known as dyer’s knotweed or Polygonum tinctorium, a native to Japan, and the True Blue project focuses on the cultivation and use of this plant .

Polygonum tinctorium has multiple varietals, such as “senbon” with red flowers and rounded leaves, and “kojoko” with white flowers and pointed leaves 22.

INDIGO CONTENT The Handbook of Natural Colorants23 includes a literature review of the indigo content of various plant sources . It reports the fresh-leaf indigo content in Polygonum tinctorium from five separate studies, giving an average yield of 0 5. 7% and ranging from 0 1. 3% Rebecca Burgess harvesting Polygonum tinctorium with a sickle (Photo by Paige Green) to 1 2. 4% . The same report presents six studies on Isatis species, giving indigo contents ranging from 0 0. 2% to 0 8. 0% PURITY Other sources suggest different purities with an average of 0 1. 9% . Vuorema25 provides a helpful overview for indigo powder from Polygonum tinctorium . For example, the purity These values refer only to the indigo of the considerations in indigo purity: of natural indigo powder sold by content of the plant leaves, where “Natural indigo contains besides indigo, Stony Creek Colors is advertised indigo is most highly concentrated . impurities such as indirubin, indigo- as approximately 40%, and purities The stems of the plant have much lower brown, indigo gluten and mineral claimed by other producers can range indigo contents, and their inclusion in matter. The indigo purity has been from about 20% to 50% . dye extraction processes would result in reported to be for woad indigo 20-40%, lower yields than those reported above . for P . tinctorium up to 12%26 and for These values are far lower than those achieved with synthetic indigo, with Indigofera species are generally Indigofera indigo the highest from 50 purities routinely exceeding 90% . recognized to be the highest in indigo up to 77%. There is also the question of the efficiency of the extraction, the content, and exceptional samples of Consistency is also a key consideration . theoretical yield of the indigo formation Indigofera tinctoria might yield indigo For most large-scale producers, from indoxyl molecules have been to values of 3 5%. of the dry leaf weight . inconsistency between batches of discovered to be approximately 60%. There have been, however, no published indigo will represent a problem for So 40% of the indoxyl is lost during the studies using modern techniques quality control . For some smaller-scale process to impurities such as isatin and to determine indican content of producers or artisans, however, the indirubin and other by-products of the Indigofera leaves, and the absence of complexities of the natural dye and the reaction.” such information makes it difficult to slight variation between batches can compare the efficiency of Indigofera to actually be desirable and presented as 24 that of other crops . features of the product line .

22 Personal correspondence from Rowland Ricketts 23, 24 Bechtold, T ;. Mussak, R . (2009) “Handbook of Natural Colorants” 25 Vuorema, A . (2008) “Reduction and Analysis Methods of Indigo” 26 Bechtold, T . et al . (2002) “Process balance and product quality in the production of natural indigo from Polygonum tinctorium Ait . applying low-technology methods”

Indigo Overview 9 Effluents from an indigo factory27

Limitations of As argued in a 2015 article in The Consequently, GoodEarth employs natural indigo Guardian,29 natural dyes in general have both natural and synthetic dyes in its serious consequences in industrial-scale clothing and linen collections. Even naturally-sourced indigo presents production, and alternative solutions problems as an industrial-scale and innovations are needed if we are Ultimately, the problem hinges on dyestuff, including the large amounts of to meet the demands of industry . The a larger issue. ‘The world has gone land and water employed in the process article quotes Simran Lal, the CEO consumption-mad,’ Patterson says. and the production of highly alkaline of India’s GoodEarth luxury clothing ‘As a result there are enormous amounts and dye-laden wastewater . brand, and Phil Patterson, a UK-based of textiles produced.’ He argues that textile consultant: consuming less is the only way to make Plant-based natural indigo makes up an impact in the long run.” less than one percent of the indigo “[GoodEarth’s Lal argues that] natural dye currently produced worldwide . If fabrics and dyes are a luxury product, the total annual production of indigo not suitable for mass consumerism. dye was sourced from plants, it would ‘Given the complexities of creating require something on the order 2 natural dyes and the resources required, 28 million acres of cultivated land . That such as water and land against the vast area is equivalent to the area of a square commercial markets across the globe, it’s roughly 56 miles to a side . not possible to use only natural dyes.’

27 http://www .noorism c. om/single-post/2015/12/05/DIRTY-DENIM 28 Based on indigo process modeling that is presented in an upcoming Fibershed report on indigo dye extraction 29 The Guardian (2015) “Natural dyes v synthetic: Which is more sustainable?”

Indigo Overview 10 The Indigo Process

MO MET SUKU HOD

Drying Composting

RACTION EXT MET TER HO WA D Leaf Sukumo Separation

Pigment Formation, Filtering & Drying Pigment Extraction

Dyeing Dye Production INDIGO EXTRACTION Composting at End of Use

Harvesting

Field Preparation with Compost

Planting Growing

he ideal indigo dye system would Planting greater flexibility and the possibility of Tbe a closed-loop system that moves automation in the transplanting step . from soil to dye to textiles and back to While indigo can be planted directly in soil . The process of producing indigo the field, it is usually desirable based Polygonum tinctorium likes a neutral, dye has three key steps: planting, on climate and yield to start seedlings well-drained soil, full sun, and weekly harvesting, and dye extraction . Dye in a greenhouse and to later transplant watering . In the Northern California extraction can be carried out using them into the field . Such seedlings can Fibershed, indigo is transplanted in late either the water extraction method be started by broadcasting seeds onto April to mid-May . or the sukumo method . Planting, open beds or by planting into flats . Transplanting can be completed with harvesting, and dye extraction are While the broadcasting method is the varying levels of automation, and the explored in detail in two separate simplest, the seedlings produced are ideal solution for a given producer will documents, and here we provide an generally only transplantable by hand . depend on the size of the cultivated area overview of each . Starting seedlings in flats allows for and the availability of capital .

Indigo Overview 11 For home-scale to scales of hundreds Harvesting Timing is very important, as the of acres, methods range from indigo concentration in the plants Polygonum tinctorium is typically transplanting by hand to using hand- can vary greatly throughout the year harvested twice per year . In the held tools, walk-behind machines, semi- (as does, of course, the size of the Northern California fibershed, the first automated tractor-mounted machines, plants themselves) . As seen below, harvest occurs around late June or early and fully-automated tractor-mounted indigo concentrations in Polygonum July . The second harvest occurs around systems . We give recommendations and tinctorium are related to the levels of late August, and the plant is then an overview of planting methods in a photosynthetically active radiation . allowed to go to seed . separate document .

Changes in photosynthetically active radiation (PAR), indican content and potential indigo yield in Polygonum tinctorium from trials in central Italy30

There is an opportunity to optimize Depending on scale of production process . Both methods serve to convert indigo yield by varying the number and available capital, the ideal naturally-occurring indican in the plant and timing of harvests, and the ideal harvesting method can range from cells into indigotin pigment and to parameters will depend on location and hand-harvesting to using walk- concentrate this pigment into a usable the variety of indigo used . Until more behind harvesting machines or dyestuff . The water extraction method research has been completed along tractor-mounted systems . We give accomplishes this in the liquid state, these lines, we recommend harvesting recommendations and an overview and the sukumo method accomplishes twice per year in mid-June/early-July of harvesting methods in a separate this in the solid state . and in late-August . For the first harvest, document . cut the plants when they are 1-2 feet tall, We have written a separate report cutting the stems several nodes up from Dye Production that focuses on the water extraction the ground . The plants will resprout and sukumo processes in detail . On from those nodes for the second The two main methods for producing the following page, we present a brief harvest, which should be completed indigo from plants are the water overview . before the plants flower . extraction process and the sukumo

30 Angelini, L . et al . (2004) “Environmental factors affecting productivity, indican content, and indigo yield in Polygonum tinctorium Ait ,. a subtropical crop grown under temperate conditions”

Indigo Overview 12 WATER EXTRACTION METHOD is complete, the remaining material The water extraction process is a (“sukumo”) is dried and bagged, ready liquid-state extraction process that for use in traditional dyeing vats . yields a powdered pigment with higher In the Japanese tradition, indigo plants indigotin purity than sukumo . Once are harvested by hand and then laid dry, the pigment is compact, relatively out to dry, occasionally being moved to homogeneous, predictable, and shelf- ensure even drying . stable . Once the leaves are dry but the stems The basic steps of water extraction are still soft and flexible, people stomp include extraction, alkalization, on the drying plants, crushing the dry oxidation, and filtration . In the leaves into small pieces and separating extraction step, the plants are them from the stems . The stems submerged in water then heated and/or are then composted and the leaves Indigo pigment from fermented to pull the indigo precursor 31 collected . Polygonum tinctorium indican out of the plant cells and into solution . Once in solution, the indican The dry indigo leaves are piled on undergoes hydrolysis (via enzymatic a ‘compost pad’ (a particular floor and/or microbial actions) and cleaves construction that allows for good into indoxyl and a sugar . After moisture drainage) . The pile must extraction is complete, the spent plant contain at least about 450 lbs of dried material is separated and set aside . leaves for effective heat-retention and The remaining indoxyl-laden liquid is composting, and in practice piles can first alkalized (given a basic pH) then weigh many thousands of pounds . oxidized (usually through aeration), producing indigotin . The insoluble Over a period of 100 days the compost indigotin precipitates, settles, and is pile is carefully turned and mixed, with filtered, optionally rinsed, and finally water and various amendments being dried to produce indigo powder . added to the pile to keep it biologically active . Over time this process reduces SUKUMO METHOD the mass and volume of the leaves Sukumo from Polygonum tinctorium by roughly 75%, concentrating the (Photo by Paige Green) The sukumo process uses composting to concentrate (rather than extract) indigo . Processes other than simple the pigment found in indigo plants . concentration are likely occurring due In the general process, plants are first to microorganisms and their byproducts harvested and dried . The leaves are interacting with the indigo compounds, then separated and composted for but this is not well understood . approximately 100 days, with frequent turning of the pile . After composting

31 Photo by Kori Hargreaves (http://www e. cotonethreads c. om/?p=247)

Indigo Overview 13 THE PROCESS OF DYEING WITH Reduction of indigo into leuco-indigo Teachers & Supplies INDIGO POWDER AND SUKUMO can be achieved in a number of ways, Michele Garcia (workshops & videos) Both indigo powder and sukumo including biological and chemical http://www .michelgarcia f. r contain indigotin, the blue pigment in methods . Sukumo is typically reduced https://naturaldyeworkshop c. om/clips/ indigo dye . When using either indigo biologically in large vats using a powder or sukumo for dyeing, the traditional process that involves water, Aboubakar Fofana (workshops) water-insoluble indigo molecules are wood ash, limestone, and wheat germ . http://www ab. oubakarfofana c. om chemically reduced in a dye bath and Artist and professional indigo dyer http://aboubakarfofanaworkshops . converted into a green-colored water- Rowland Ricketts trained in indigo bigcartel c. om soluble form known as leuco-indigo . growing and dyeing in Japan and Catherine Ellis (workshops) This dissolved leuco-indigo saturates practices the Japanese sukumo method https://www el. listextiles c. om/teaching/ textiles when they are dipped into the in his work . He provides an excellent illustrated overview of the process on vat, and when the textile is removed John Marshall (workshops) his website: and exposed to atmospheric oxygen the http://www j. ohnmarshall t. o/J- leuco-indigo oxidizes again to water- http://www .rickettsindigo . com workshopsLectures .htm insoluble indigotin, and the pigment adheres to the fibers . As the leuco- Indigo powder can be reduced with Barbara Shapiro (workshops) indigo oxidizes into indigotin, the color natural materials33, 34 such as fructose, http://www b. arbarashapiro c. om of the textile changes dramatically from ferrous sulfate, henna, osage, and Threads of Life (workshops) greenish to indigo blue . For efficient madder, or with synthetic compounds http://threadsoflife c. om/workshops/ conversion from leuco-indigo, indigo such as sodium hydrosulfite and dye vats require an alkaline pH32, which thiourea dioxide . Kathy Hattori, Botanical Colors can be achieved with the addition of (workshops and supplies) alkalizers such as calcium hydroxide, We do not address specific methods for https://botanicalcolors c. om a derivative of limestone . The ideal pH indigo dyeing in this document . for dyeing cotton is around 9-9 5. and for Maiwa (workshops and supplies) For more resources, we recommend the dyeing wool is around 11-11 5. 32. http://www .schooloftextiles c. om following books, online materials, and https://maiwa c. om/collections/indigo teachers . Noon by Jane Palmer Books (workshops and supplies) The Modern Natural Dyer https://www .noonbyjanepalmer c. om/ by Kristine Vejar Stony Creek Colors Natural Color (domestic natural indigo) by Sasha Duerr https://stonycreekcolors c. om Harvesting Color Indigotin (water insoluble, blue) by Rebecca Burgess

A Handbook of Indigo Dyeing by Vivian Prideaux

Leuco-indigo (water soluble, green)

32 Bechtold, T ; Mussak, R (2009) “Handbook of Natural Colorants” 33 http://box19 c. a/maiwa/pdf/organic_vat_data p. df 34 http://www a. urorasilk c. om/tutorials/how_to_natural_indigo_dye_vat .html

Indigo Overview 14 Conclusions

or its rich history, cultural indigo and highlighted the need for Fsignificance, beauty, low toxicity, larger cultural and systemic shifts . performance, practicality, and the opportunity to reimagine a highly We believe plant-based indigo is polluting industry, natural indigo one of the best available options for presents a great opportunity, and regionally focused dye projects . We view supporting a local industry is a natural dye farming as an important compelling goal for Fibershed and facet of integrated food and fiber those who share its values . farming projects that can support local economies . To have the desired The indigo process has three basic effect on culture and industry, however, steps: planting, harvesting, and dye we believe natural indigo needs to be extraction . In this document, we part of a larger symbolic and strategic provided an overview of each, and program that recognizes direct detailed explorations are given in two competition with the vast synthetic forthcoming documents that will be indigo industry is not possible . available through Fibershed by late- summer 2017 . We recommend pairing regional natural dye projects with efforts to shift culture In this document, we also presented and our patterns of consumption the various sources of blue dye and of through building appreciation, respect, indigo, and motivate the use of plant- and understanding for the resources, based indigo in particular . We identified skill and labor required to make plant- the limitations of natural dyes like based blue a reality for modern wearers .

Indigo Overview 15