Dissolve, then return

The blog "Aibatake", which records an indigo field in Okinawa, describes one stage of making doro-ai (mud indigo). Harvested Ryukyu indigo (Ryukyu-ai) is soaked in water, stems and all, and left to ferment for several days. Slaked lime is then dissolved little by little into the yellow-green liquid, with stirring, once the stems and leaves have been removed. The indoxyl in the liquid oxidises and becomes blue indigo. In time the liquid separates into a clear upper layer and a precipitate, and the settled indigo, once collected, is the doro-ai. That is what the record describes.^[1] The same change of colour can be seen the moment cloth is lifted out of an indigo vat. In its entry "Indigo", Asian Textile Studies explains that reduced indigo is a pale yellow, and that in cloth exposed to air oxidation proceeds, passing through a greenish blue on the way to blue. Cotton Incorporated says that indigo, reduced to a very pale greenish yellow, begins to turn back to blue as soon as it meets the air.^[2] Oxidation here means losing electrons, and reduction means gaining them. This theme is about the place where that mechanism is most easily seen.

Why does a pigment that does not dissolve in water dissolve into a liquid once, and then return to its original colour on the cloth? Some sources say the same description applies not only to indigo but also to Tyrian purple and to sulfur dyes. The way the pigment is dissolved, however, differs greatly: by fermentation, by chemicals, or inside the body of a shellfish. We look at what the cases share, and at how they differ by region and by method.

According to Yoshiko Minami's account, the leaf cells of the Persicaria tinctoria plant (ai) accumulate large amounts of indican, a glycoside (a compound joined to a sugar).^[1] When the leaf is damaged, the enzyme β-glucosidase hydrolyses indican into indoxyl and glucose.^[2] Indoxyl is described as extremely unstable: on contact with oxygen in the air, its molecules link up without any help from an enzyme and become stable, insoluble indigo.^[3] The reaction that the same source records, in which crushing a leaf turns your fingertips blue, is where indigo dyeing begins.^[2]

Evidence for this paragraph (3)

[1]

Persicaria tinctoria contains Indicancontextual

Scope: The Polygonaceae plant “ai” (named Polygonum tinctorium in this source)

Source: タデ科植物アイのインジカン代謝 （南善子, 2001） ・p.202（本文冒頭） ・textbook ・ checked against the source by AI

[2]

Indican produces Indoxylcontextual

Scope: When the leaf cells of ai are disrupted

Source: タデ科植物アイのインジカン代謝 （南善子, 2001） ・p.203 ・textbook ・ checked against the source by AI

[3]

Indoxyl produces Indigo (indigotin)contextual

1 source: タデ科植物アイのインジカン代謝 · full evidence

Following the Kaken Test Center's explanation of vat dyes (Kaken is a Japanese textile testing foundation), to colour cloth with indigo, the insoluble indigo must first be changed into leuco-indigo, a form that dissolves in water. It is then worked into the fibre and exposed to air, which returns it to the original insoluble indigo.^[1] The centre's explanation of sulfur dyes likewise says that the insoluble dye is reduced and dissolved, taken up by the fibre, and then exposed to air so that it oxidises back into the original insoluble dye.^[2] The name of this theme, "Dissolve, then return", refers to this round trip, which indigo and sulfur dyes share.

Evidence for this paragraph (2)

[1]

vat dye works by reduction to a soluble form and re-oxidationcontextual

Source: 建染染料（バット染料） （一般財団法人カケンテストセンター） ・本文1文目 ・institutional summary ・ checked against the source by AI

[2]

sulfur dye works by reduction to a soluble form and re-oxidationcontextual

Source: 硫化染料 （一般財団法人カケンテストセンター） ・本文1文目 ・institutional summary ・ checked against the source by AI

The "dissolving" step, which is called building the vat, comes in two broad kinds: the fermentation vat and the chemical vat. Miyoko Kawahito explains the difference. In a chemical vat, a chemical reducing agent itself reduces the indigo directly. In a fermentation vat, by contrast, one has to make indirect arrangements, supplying the nutrients and the conditions that the reducing bacteria and the reducing enzyme they produce need.^[1] What actually does the reducing in a fermentation vat is not the bacteria themselves but the reducing enzyme they produce and activate.^[2] In Kawahito's account of the Awa-ai fermentation vat, the best temperature for activating the reducing enzyme is 45 to 50°C, while the bacteria themselves grow best at 30°C, and the alkalinity best for producing the enzyme is around pH 11.0.^[3][4] The materials that keep the vat alkaline also differ. Kawahito explains that slaked lime dissolves poorly in water, so its effect lasts, whereas sodium hydroxide dissolves readily and acts quickly, but its effect does not last.^[5] Dharma Trading Co. describes its "Pre-Reduced Indigo Crystals" as a home-use product: a synthetic indigo that has already been reduced by 60%, so the vat can be built with soda ash (sodium carbonate), which is milder.^[6]

Miyoko Kawahito describes sukumo, the raw material of Japanese indigo dyeing, as made by fermenting dried indigo leaves. She distinguishes this from the precipitation method, in which fresh leaves are soaked in water to extract the pigment, and treats the two as different ways of processing natural indigo.^[1] The sources disagree on the details of making sukumo. A record from Aizumi Town in Tokushima puts the turning of the pile ("kirikaeshi") at about 20 times over about 100 days. The Ai-no-ie ("House of Indigo") laboratory at Shikoku University gives 12 to 15 times, and Miyoko Kawahito (2015) gives 22 to 23 times over 90 to 100 days.^[2][3][4] They appear to be describing the same step, but this site cannot judge whether the difference lies in what counts as one turn, or in differences between indigo makers or scales of work. According to Anna Hartl and colleagues, lime was used in large quantities in China and North-East India, but only in small amounts in late-19th-century British India. The use of lime in the precipitation method also varies from one producing region to another.^[5]

Evidence for this paragraph (5)

[1]

Sukumo ・differenceKawahito Miyoko divides indigo dye into natural and synthetic indigo, with natural indigo further divided by processing method into 'sukumo' and 'chindenai' (precipitated indigo): sukumo is made by drying then fermenting indigo leaves, whereas chindenai is made by soaking fresh leaves in water to extract the pigment.contextual

1 source: 阿波藍の製造（藍師・栽培・染料作り）とその染料液の作成 · full evidence

[2]

Sukumo ・mechanismAccording to Aizumi Town, the piled leaves (one 'toko' or bed) are turned about 20 times in the 'kirikaeshi' process so that fermentation proceeds evenly, and this heavy labour is said to continue for roughly 100 days.contextual

1 source: すくもの加工 · full evidence

[3]

Sukumo ・mechanismThe Ai-no-ie laboratory at Shikoku University targets roughly 250 kg of finished sukumo, with the core temperature of the piled leaves reaching about 70°C. Kirikaeshi is done at least once a week, and repeating it 12 to 15 times while supplying air and moisture is said to complete the sukumo.contextual

1 source: 「すくも」づくり · full evidence

[4]

Sukumo ・mechanismAccording to Kawahito Miyoko, after 12-13 turns, 'naka-doshi' (sieving) is performed in late October; after the 17th-18th turn in November, 'age-doshi' is performed; and Awa-ai is finished after a total of 22-23 turns. Timing varies somewhat by ai-shi, but finishing is said to take 90-100 days between September and January.contextual

1 source: 阿波藍の製造（藍師・栽培・染料作り）とその染料液の作成 · full evidence

[5]

Indigo precipitation method ・propertyThe amount of lime used differs by production region: large quantities in China and North-East India, but only small amounts (as lime water) in late-19th-century British India. Lime raises the pH and speeds the conversion of indoxyl to indigotin, and acts as a precipitant, but it is not essential, and if not removed it dilutes and lowers the indigotin content.contextual

Source: “Purplish Blue” or “Greenish Grey”? Indigo Qualities and Extraction Yields from Six Species （Anna Hartl; Andrea Polleichtner; Johannes Novak, 2024） ・§1.2 ・textbook ・ checked against the source by AI

The sources also give different answers to what the word "hon-ai" (literally "true indigo") refers to. Mizuno Dye Works classifies dyeing as "hon-ai-zome" as long as a plant indigo is used as the dye, even if chemicals such as reducing agents are used.^[1] Riku Matsuzaki, an indigo dyer in Kyoto, says that within the sources he has looked at, he could find neither "hon-ai" nor "hon-ai-zome" as a term, and that the word began as a self-description by producers in Tokushima (Awa).^[2] Sinkukan, a shop selling denim and workwear, gives its own view that within Japan "hon-ai" should be limited to goods dyed with sukumo indigo (Persicaria tinctoria) alone. It points out that "wari-date", a vat blending sukumo indigo with cheaper chemical indigo, is in some cases sold as "hon-ai-zome".^[3][4] The three definitions differ, and this theme does not choose one of them as correct.

Evidence for this paragraph (4)

[1]

"Hon-ai" ・attributed toMizuno Dye Works states that as long as a dye made from indigo plants (such as Persicaria tinctoria) is used, a product is classified as "hon-ai-zome" even when chemical reducing agents were used in the dyeing process; conversely, if the dye itself is a chemical dye (such as the chemical indigo dye used for blue jeans), the product does not count as hon-ai-zome.contextual

Scope: Mizuno Dye Works' explanation

Source: 本藍染と正藍染の違いとは？意外と知らない藍染の豆知識 （水野染工場, 2023） ・「そもそも本藍染って何？」の節 ・manufacturer statement ・ checked against the source by AI

[2]

"Hon-ai" ・attributed toRiku Matsuzaki, an indigo dyer in Kyoto, states that within the historical sources he has traced, he could not find the terms "hon-ai" or "hon-ai-zome" themselves at all, and that the term originated when producers in Awa (Tokushima) began calling their own Awa indigo the "real" (hon-ai) one, distinguishing other regions' indigo as inferior "ji-ai."contextual

Scope: Riku Matsuzaki's personal view, based on his own review of historical sources

Contradicting source: 本物の藍染＝本藍は間違えています （松崎陸（京藍染師）, 2020） ・「本藍とは何か」から始まる段落(徳島の自称の由来)、および「僕が掘り下げた知識、歴史では」以降の段落(本藍という言葉が見つからないという段落) ・practitioner's record ・ checked against the source by AI

[3]

"Hon-ai" ・attributed toSinkukan, a denim and workwear shop, states that within Japan the word "hon-ai" is usually associated with sukumo indigo (from Persicaria tinctoria), and states as its own view that, within Japan, the term "hon-ai-zome" should be reserved for goods dyed using sukumo indigo alone.contextual

Scope: Sinkukan's stated view (explicitly framed as "our shop's view")

Source: 本藍染めについて （真空館） ・「本藍(天然藍)とは」の節、および「当店の見解としては」の一文 ・manufacturer statement ・ checked against the source by AI

[4]

"Wari-date" (blended vat) is attributed to "Hon-ai"contextual

Scope: Sinkukan's stated view

Source: 本藍染めについて （真空館） ・「割り建て」の段落(「また本藍(すくも藍)と化学藍をブレンドして染める方法を、割り建て(わりだて)と言います」から「『絞り』などの白柄も消えてしまいます」まで) ・manufacturer statement ・ checked against the source by AI

Tyrian purple starts with a different pigment. Christopher Cooksey's review gives its main component as 6,6'-dibromoindigo, and explains that, unlike unbrominated indigo, it carries two bromine atoms at the 6 and 6' positions.^[1] Apsana Ngangbam and colleagues, drawing on earlier studies, explain that the pigment arises from a precursor, tyrindoxyl sulfate, held in the mollusc's secretory gland. After hydrolysis by an enzyme, it passes through spontaneous oxidation and photolysis (a reaction in which light breaks up molecules) to become purple. Unlike indigo, the last step needs light.^[2] That is about how the pigment forms, not about getting it into cloth. A report of a demonstration by the dye workshop tezomeya records a rule of thumb about handling the pigment once it has been reduced and turned yellow: strong light turns it into indigo, so the room lights are switched off while working.^[3] However, we found no description in the academic papers checked for this site of an experiment confirming this light-driven change, that is, the loss of bromine. A paper by Jesús Emilio Michel-Morfín and colleagues includes, in the form of a citation, an account of commercial harvesting on Mexico's Pacific coast in the 1980s, in which the interval between milkings was not considered, causing mass mortality among the snails.^[4]

Evidence for this paragraph (4)

[1]

6,6'-Dibromoindigo (Tyrian purple) differs from Indigo (indigotin)contextual

2 sources: Preparation of Tyrian Purple (6,6'-Dibromoindigo): Past and Present; ジブロモインジゴ dibromoindigo · full evidence

[2]

Tyrindoxyl sulfate produces 6,6'-Dibromoindigo (Tyrian purple)contextual

Scope: as reported for Dicathais orbita

Context source: Bromoperoxidase Producing Bacillus spp. Isolated from the Hypobranchial Glands of A Muricid Mollusc Are Capable of Tyrian Purple Precursor Biogenesis （Apsana Kh. Ngangbam; Peter Mouatt; Joshua Smith; Danielle L. E. Waters; Kirsten Benkendorff, 2019） ・Introduction ・institutional summary ・ checked against the source by AI

[3]

6,6'-Dibromoindigo (Tyrian purple) ・propertyThe workshops report explains that because this pigment, while in its reduced yellow state, is said to convert into indigo (the pigment of indigo dyeing) on exposure to strong light, the workshop keeps the room lights off during this step.contextual

Scope: explanation given in connection with a modern dye workshop's demonstration

Source: アカニシ貝紫染めワークショップの報告 （tezomeya（草木染めの天然色工房、店主）, 2019） ・記事本文、部屋を暗くしている理由の説明部分 ・practitioner's record ・ checked against the source by AI

[4]

Plicopurpura pansa ・why it fell out of useThe paper, citing Turok et al. (1988), describes a Japanese companys commercial exploitation on Mexicos Pacific coast in the 1980s, dyeing silk kimono threads with the snails purple, which caused high mortality through poor management because the interval between milkings was not observed.contextual

Scope: Mexican Pacific coast, 1980s, as cited by the paper from Turok et al. (1988)

Source: Estructura de la población, esfuerzo y rendimiento de tinte del caracol Plicopurpura pansa (Gould, 1853) en el Pacífico mexicano （Jesús Emilio Michel-Morfín; Ernesto A. Chávez; Lourdes González, 2002） ・本文、種の概要説明部分（スペイン語） ・historical record ・ checked against the source by AI

Sulfur dyes are explained by the same mechanism, but they are not a single compound like indigo. In "Dye Chemistry for Dyeing Technologists" (part 5), a series in the Journal of the Textile Machinery Society of Japan, Kunihiko Imada describes commercial sulfur dyes as mixtures of complex compounds. Because a single chemical structure cannot represent them, the Colour Index does not list a structure for them, and gives instead the starting intermediate and its sulfurisation product.^[1] Imada notes that in stored goods dyed with sulfur dyes, some of the loosely bound sulfur can oxidise and produce sulfuric acid, which makes the fibre brittle. The BOKEN Quality Evaluation Institute reports an assessment case in which the black area of a yukata fabric stored for 15 years tore. Its tensile strength, the strength that shows how hard the fabric is to break when pulled, fell far below the benchmark, and its pH was acidic at 2.9. Sulfate ions were also detected, and the dye was presumed to be a sulfur dye or a sulfur vat dye.^[2][3] The patterned area of the same cloth (a direct dye) was not damaged.^[3]

Evidence for this paragraph (3)

[1]

sulfur dye ・containscommercial sulfur dyes are said to be complex mixtures that cannot be represented by a single chemical structure, so the Colour Index does not list a structure for them but instead shows the starting intermediate and its sulfurisation productcontextual

Source: 染色技術者のための染料化学（その5）4.硫化染料 （今田邦彦, 2002） ・P246、4.2節(2)①一般硫化染料 ・textbook ・ checked against the source by AI

[2]

sulfur dye ・causesduring storage, part of the unstably bound sulfur in the dyeing is said to oxidise under the influence of atmospheric moisture and oxygen, generating sulfuric acid that can embrittle the fibre (especially cellulosic fibre)contextual

Scope: A combined statement from several sources (a dye-chemistry article, cleaning-industry incident reports, a dye shop and a testing lab); "the influence of moisture and oxygen in the air" is the incident reports' wording

Source: 染色技術者のための染料化学（その5）4.硫化染料 （今田邦彦, 2002） ・P246、4.1節 ・textbook ・ checked against the source by AI

Source: 衣料管理情報（クリーニング注意情報）「硫化染料による綿の脆化・破損」 （全国クリーニング生活衛生同業組合連合会（監修：クリーニング綜合研究所）, 2019） ・「硫化染料による繊維の脆化」の項 ・practitioner's record ・ checked against the source by AI

Source: 衣料管理情報（クリーニング注意情報）「硫化染料による脆化破損」 （全国クリーニング生活衛生同業組合連合会（監修：クリーニング綜合研究所）, 2023） ・「硫化染料による繊維の脆化」の項 ・practitioner's record ・ checked against the source by AI

Source: 硫化染料（やさしい染料講座） （岩瀬商店株式会社（ソメラボ）, 2020） ・本文 ・manufacturer statement ・ checked against the source by AI

Source: 教えてボーケンくん No.7 硫化染料使いの製品の破れ発生 （一般財団法人ボーケン品質評価機構） ・1頁目「原因は…」の段落および補足「硫黄と脆化」 ・analytical ・ checked against the source by AI

[3]

sulfur dye ・causesin an actual assessment case, the black area (cotton 100%) of a yukata fabric stored for 15 years tore: its tensile strength fell far short of the general 200 N benchmark, its pH was acidic (2.9), sulfate ions were detected, and dye-class identification indicated a sulfur or sulphur-vat dye (the patterned area, by contrast, was identified as a direct dye and did not tear)contextual

Source: 教えてボーケンくん No.7 硫化染料使いの製品の破れ発生 （一般財団法人ボーケン品質評価機構） ・1頁目、STEP1〜3の試験結果 ・analytical ・ checked against the source by AI

• Synthetic or natural: Miyoko Kawahito says that when only synthetic indigo is used, only a chemical vat is possible, whereas with natural indigo alone, or a mixture of natural and synthetic, either a fermentation vat or a chemical vat can be built.^[1] Dharma explains that synthetic indigo is chemically identical to natural indigo.^[2] The Russian source on hand-block vat printing, by V. Korolkova, says that a "full chemical analogue" of natural indigo was invented in late-19th-century Germany.^[3] Taking the three sources together, this site reads the difference between synthetic and natural as lying in how the vat is built rather than in the pigment itself. This is this site's reading. No single source says so.
• The conditions in the vat are not a single set: the pH and temperature above are figures for the Awa-ai fermentation vat. Keiichi Aino and colleagues say that the bacteria that build a woad vat (woad is the European indigo plant) suit a different pH and temperature from the bacteria of sukumo.^[4] In Dharma's procedure for a chemical vat, the ideal temperature is 35 to 38°C and the pH is around 10. When checking the vat, its guide is to add reducing agent if blue specks appear near the surface or the whole liquid looks bluish, and to add soda ash if white specks or milkiness appear.^[5][6]
• Setting up a vat (home kits): the kit from Jacquard Products has you add soda ash, pre-reduced indigo and then sodium hydrosulfite (a chemical that reduces indigo, called "hydro" for short), in that order, to warm water. You stir in one direction, then reverse, cover the vat and leave it for 15 to 30 minutes.^[7] Dharma's procedure says that if you reverse the stirring and run the stick along the rim as you take it out, the foam, called the "flower", gathers in the centre.^[8]
• Comparing the precipitation method: according to Yukari Owan of the Okinawa Prefectural Museum and Art Museum, the stems and leaves are soaked in water and left to ferment for several days, and the leaves are then removed. When lime is added and the liquid is stirred, the indigo component settles together with the lime.^[9] In an experiment by Hartl and colleagues, a traditional method using lime at ambient temperature was compared with a standard method at high temperature without lime. They report that the former gave a larger amount but a lower indigotin content.^[10]
• Affinity and ring dyeing: Cotton Incorporated, which handles information on cotton products, says that indigo's affinity for cotton fibre (the tendency of a dye, under given conditions, to stay on the fibre rather than in the liquid) is far lower than that of almost any other dye. As a result, industrial rope dyeing leaves only the outside of the yarn dyed, which is called "ring dyeing". It says that with any other dye this would be considered a defect.^[11] David Richardson and Sue Richardson, in Asian Textile Studies, say that with ring dyeing the pigment in the outer layer of the fibre is easily rubbed off, which contributes to the faded look of denim.^[12]
• Reducing and oxidising agents, and waste water (sulfur dyes and chemical indigo vats): according to Kunihiko Imada, sodium dichromate, which has long been used in the oxidation step for sulfur dyes, is falling out of use because of the problem of chromium in waste water.^[13] Aino and colleagues say that when sodium dithionite is used for reduction in a chemical indigo vat, by-products such as sodium sulfate and sulfite and thiosulfate ions are produced. Changhai Yi and colleagues say that in industrial denim dyeing, excess hydrosulfite pollutes water and air through sulfur-based by-products.^[14][15] Maiwa explains that it chose thiourea dioxide for its kit because it keeps well and can be disposed of safely.^[16]
• The conditions for a fermentation vat (the optimum temperature and pH for the enzyme) and those for a chemical vat (the concentration and temperature of reducing agent and alkali) differ greatly, even within this one theme. Take care not to generalise them to indigo dyeing as a whole without checking which kind of vat and which fibre a statement applies to.

Evidence for this paragraph (16)

[1]

Chemical vat ・applies toWhen only synthetic indigo is used, the chemical vat is the only option; when natural indigo is used alone, or as a mixture of natural and synthetic indigo, either the fermentation vat or the chemical vat can be used.contextual

Source: 連載〈阿波藍5〉染料液の作り方（藍を建てる） （川人美洋子, 2010） ・P-284,「藍を建てる」の段落 ・practitioner's record ・ checked against the source by AI

Source: Indigo — Natural Dyes （Maiwa） ・"THE WORKHORSE VAT"の項全体 ・manufacturer statement ・ checked against the source by AI

Source: インド藍　粉末（商品ページ） （株式会社田中直染料店） ・商品説明本文 ・manufacturer statement ・ checked against the source by AI

[2]

Pre-Reduced Indigo Crystals is a type of Leuco-indigo (reduced indigo, "indigo white")contextual

2 sources: Pre-Reduced Indigo Crystals (product page, Description + Instructions tabs); Pre-Reduced Indigo Instructions · full evidence

[3]

Kubovaya naboyka (Russian indigo vat-dye resist block printing) ・why it fell out of useStates that in the early last quarter of the 19th century Germany invented a full chemical analogue of natural indigo, and shortly after that a stable chemical preparation, hydrosulfite, needed to convert indigo into a water-soluble form; the synthetic blue dye came to be widely purchased in Russia, and the craft receded from central Russia toward the northern and eastern provinces, where it reportedly persisted in peasant life until the 1940s.contextual

Source: Технология ручной кубовой набойки XIX-начала XX вв. на территории Владимирской области （В. Королькова (Живая нить традиций. Владимирская область / Традиции33)） ・「В начале последней четверти XIX в. в Германии был изобретён полный химический аналог...」および「Постепенно из Центра России кубовая набойка вытеснялась...」の段落 ・institutional summary ・ checked against the source by AI

[4]

Clostridium isatidis differs from Reducing bacterium ("Bacillus alkaliphiles")contextual

Source: Microbial Communities Associated With Indigo Fermentation That Thrive in Anaerobic Alkaline Environments （Keiichi Aino; Kikue Hirota; Takahiro Okamoto; Zhihao Tu; Hidetoshi Matsuyama; Isao Yumoto, 2018） ・"Studies on Woad Dye Fermentation Vats" 節 ・textbook ・ checked against the source by AI

[5]

Chemical reduction of indigo (chemical vat) ・property ― Temperaturecontextual

Scope: Vat maintenance for Dharma Pre-Reduced Indigo Crystals

Source: Pre-Reduced Indigo Instructions （Dharma Trading Co.） ・"Temperature"・"Ph"の項 ・manufacturer statement ・ checked against the source by AI

[6]

Pre-Reduced Indigo Crystals ・propertyDuring vat maintenance: if blue specks appear near the surface or the liquid looks more blue than yellow-green, dissolve half a teaspoon of thiourea dioxide or sodium hydrosulfite in a cup of warm water and add it; if white specks or milkiness appear, add a teaspoon of soda ash dissolved in warm water; if the colour looks grey and weak, add one to two teaspoons of pre-reduced indigo; after any addition, let the vat rest about 15 minutes before checking again.contextual

Scope: Vat maintenance for Dharma Pre-Reduced Indigo Crystals

Source: Pre-Reduced Indigo Instructions （Dharma Trading Co.） ・"Keeping your Indigo Vat happy:"の段落群 ・manufacturer statement ・ checked against the source by AI

[7]

Jacquard Indigo Tie Dye Kit works by Chemical reduction of indigo (chemical vat)contextual

Scope: Vat set-up procedure for the Jacquard Indigo Tie Dye Kit

Source: Indigo Tie Dye Kit Instructions (booklet, PDF) （Jacquard Products (Rupert, Gibbon & Spider, Inc.), 2023） ・PDF P5「Setting up the indigo vat」手順1〜6 ・manufacturer statement ・ checked against the source by AI

[8]

Pre-Reduced Indigo Crystals works by Chemical reduction of indigo (chemical vat)contextual

Scope: Vat set-up procedure for Dharma Pre-Reduced Indigo Crystals

Source: Pre-Reduced Indigo Instructions （Dharma Trading Co.） ・"Directions:"の段落 ・manufacturer statement ・ checked against the source by AI

[9]

Indigo precipitation method ・mechanismIn the Okinawan precipitation method, harvested leaves and stems of Ryukyu indigo are soaked in water and left to ferment for several days, then the leaves are removed and lime is added to the remaining liquid and stirred. With sufficient agitation the indigo component in the liquid attaches to the lime and precipitates; the supernatant is gradually drawn off, and finally the precipitated indigo is dewatered and concentrated with cloth to make the dye.contextual

Scope: Ryukyu indigo (Okinawa)

Source: 資料にみる琉球藍の製藍技法の比較研究 （大湾ゆかり（沖縄県立博物館・美術館学芸員）, 2025） ・1.はじめに 脚注(※沈殿法) ・institutional summary ・ checked against the source by AI

[10]

Indigo precipitation method ・propertyComparing an extraction method simulating traditional local practice (ambient temperature, with lime) against a standardised hot-extraction method without lime, the former yielded more indigo material but with a lower indigotin content; the indigotin extraction yield itself did not differ greatly.supported

Scope: Compared using Persicaria tinctoria and Indigofera arrecta grown in Austria

Source: “Purplish Blue” or “Greenish Grey”? Indigo Qualities and Extraction Yields from Six Species （Anna Hartl; Andrea Polleichtner; Johannes Novak, 2024） ・§2.2、Table 1 ・experimental ・ checked against the source by AI

[11]

Indigo (indigotin) causes Ring dyeing (white core)contextual

1 source: Denim Fabric Manufacturing (Technical Bulletin ISP 1010) · full evidence

[12]

Ring dyeing (white core) ・causesRing dyeing is said to be one reason for indigo's low abrasion fastness, since the dye in the outer layer of the fibre is easily rubbed away (as in the fading of denim); this same low fastness is also described as one of the valued features behind the faded look of blue denim.contextual

Source: Indigo （David Richardson; Sue Richardson, 2016） ・"Ring Dyeing and Substantivity" 節、冒頭 ・textbook ・ checked against the source by AI

[13]

sulfur dye requires Dichromate saltscontextual

Source: 染色技術者のための染料化学（その5）4.硫化染料 （今田邦彦, 2002） ・P248、4.4節(1)ii)酸化工程 ・textbook ・ checked against the source by AI

Context source: Salt Free Sulphur Black Dyeing of Cotton Fabric After Cationization （Muhammad Sohaib Atiq; Abdur Rehman; Kashif Iqbal; Faiza Safdar; Abdul Basit; Munir Ashraf; Hafiz Shahzad Maqsood; Asfandyar Khan, 2019） ・p.157、Conventional dyeing 節および Dyeing of cationized cotton 節 ・experimental ・ checked against the source by AI

[14]

Chemical reduction of indigo (chemical vat) ・causesReduction with sodium dithionite is reported to ultimately produce environmentally unfavourable byproducts such as sodium sulfate and sulfite and thiosulfate ions; when the waste liquor reaches a treatment system, its strong reducing power is also said to damage the activated sludge there.contextual

Scope: The chemical vat (industrial sodium-dithionite reduction)

Source: Microbial Communities Associated With Indigo Fermentation That Thrive in Anaerobic Alkaline Environments （Keiichi Aino; Kikue Hirota; Takahiro Okamoto; Zhihao Tu; Hidetoshi Matsuyama; Isao Yumoto, 2018） ・Introduction, 化学還元の環境影響に関する段落 ・textbook ・ checked against the source by AI

[15]

Sodium hydrosulfite (sodium dithionite) ・causesThis paper states that when used in excess in industrial indigo dyeing, sodium dithionite generates sulfur-related by-products such as sulfites, sulfates and toxic sulfides, causing both water pollution and air pollution.contextual

Source: Practical and environment-friendly indirect electrochemical reduction of indigo and dyeing （Changhai Yi, Xiaodong Tan, Bihan Bie, Haitao Ma, Hong Yi, 2020） ・Abstract、Introduction（「causing serious water pollution and air pollution」の一文） ・experimental ・ checked against the source by AI

[16]

Natural Indigo Thiox Kit ・attributed toMaiwa calls this its "Workhorse Vat" — its pick for dyers who want to do a lot of dyeing but don't need a vat that stays alive for months — and says thiourea dioxide was chosen as the reducer for two practical reasons: it keeps well on the shelf and can be thrown out without special precautions.contextual

Scope: Maiwa Natural Indigo Thiox Kit

Source: Natural Indigo Thiox Kit (product page) （Maiwa） ・商品説明、"This is our 'Workhorse Vat'..."の一文 ・manufacturer statement ・ checked against the source by AI

Source: Indigo — Natural Dyes （Maiwa） ・"THE WORKHORSE VAT"の節、"A REDUCING AGENT"の項 ・manufacturer statement ・ checked against the source by AI

Return to the scene we began with, in which the liquid turns from yellow-green to indigo blue once slaked lime is added, or to cloth lifted from the vat and changing colour in the air. Within the same movement of dissolving and returning lie the points where the sources part: fermentation or chemicals, sukumo or the precipitation method, and whether to call it "hon-ai" at all. The next time you hold a piece of indigo-dyed cloth, what you can tell apart is not only how deep the colour is but the conditions behind it: the kind of vat and the raw material that produced it.

Paula Burch divides the chemical methods of removing colour from a dye into two: oxidation, which takes electrons away, and reduction, which gives electrons.^[1] Burch says that vat dyes such as indigo can be stripped only with oxidising agents, and that reducing agents (such as hydro and thiourea dioxide) merely convert a vat dye to its water-soluble leuco form, which does not remove the colour.^[2] Tanaka Nao Dyeing Materials Store describes discharge, a treatment that uses chemicals to remove dye, in which cloth dyed with chemical dyes is bleached fully white with hydro. The cloth is treated for about 10 to 30 minutes in a hot solution, at 80°C or above, of hydro and other agents. The store warns that sulfur dioxide gas is given off during this treatment, so it should be done in a well-ventilated place.^[3]

Evidence for this paragraph (3)

[1]

Oxidative dye discharge differs from Reductive dye dischargecontextual

Source: FAQ: What chemicals can be used to remove or discharge dye? （Paula E. Burch, 2010） ・冒頭「What chemicals can be used to remove dye?」の段落 ・practitioner's record ・ checked against the source by AI

[2]

Reductive dye discharge differs from vat dyecontextual

Scope: Indigo and other vat dyes

Source: FAQ: What chemicals can be used to remove or discharge dye? （Paula E. Burch, 2010） ・「Fast Fade for Jeans」段落末尾の一文 ・practitioner's record ・ checked against the source by AI

[3]

Sodium hydrosulfite (sodium dithionite) ・propertyTanaka Nao Dye Store states that in discharge (bleaching) processing using ‘hydro’ (hydrosulfite-type reducing agents), fabric is treated for about 10-30 minutes in a hot (80°C or above) solution of hydro and other agents, and that because sulfurous gas is given off during the process it should be carried out in a well-ventilated place.contextual

Scope: General processing for fully discharging (bleaching out) dyed fabric with hydro (described separately from the indigo-specific discharge method)

Source: よくあるご質問 （株式会社田中直染料店, 2026） ・よくあるご質問「化学染料で染めた布を抜染ですべて真っ白にしたいのですが、どんな方法がありますか？」の回答文中 ・manufacturer statement ・ checked against the source by AI

Contradicting source: ハイドロ（ハイドロサルファイトコンク、商品ページ） （株式会社田中直染料店） ・商品説明「脱色の際は、60度まで温度を上げて浸けてください」の一文 ・manufacturer statement ・ checked against the source by AI

The same store's FAQ, however, says that cloth dyed with Sulen/Neosulen or with naphthol cannot be stripped at all by this method.^[1] The page does not say which class of dye Sulen and Neosulen belong to. Whether this agrees with Burch's explanation that reducing agents do not strip vat dyes depends on the class of these brands, which the sources do not settle. This is the site's own reading. How dyeing with naphthol works is covered in the theme "Made on the cloth".

Evidence for this paragraph (1)

[1]

naphthol (azoic) dye ・propertyIn its FAQ on discharge-printing, states that among its chemical dyes for cotton and linen, those believed to be fiber-reactive or direct dyes can mostly be discharged, but anything dyed with Sulen/Neosulen or with naphthol cannot be discharged at all.contextual

Scope: Tanaka Nao's discharge-printing FAQ for cotton/linen chemical dyes

Source: よくあるご質問 （株式会社田中直染料店, 2026） ・抜染･脱色 Q&A、ナフトールに関する記述(2箇所) ・manufacturer statement ・ checked against the source by AI

The typical oxidising bleach is household chlorine bleach (sodium hypochlorite). The BOKEN Quality Evaluation Institute explains that "isatin yellowing", in which indigo-dyed cloth turns yellow in storage, can also be related to this kind of oxidation. This yellowing can arise from three factors: residue from the decomposition of a bleaching agent, oxidative decomposition by ultraviolet light, and the action of nitrogen oxides in the air. The indigo breaks down, producing a yellow substance called isatin.^[1] BOKEN also says that because isatin dissolves in water, washing removes the yellow tint, but since it is a substance formed when the indigo is broken down, the colour after washing is paler than before.^[2] This is this site's reading: the reduction and oxidation that put colour in and the reduction and oxidation that take colour out appear to be the same mechanism, run in opposite directions.

For another way of making an insoluble colourant on the cloth, see the theme "Made on the cloth".

• 🧪 It is said that adding a lot of slaked lime at once harms the indigo colour, but has this ever been tested chemically? (Kawahito says enzyme production drops sharply above pH 11.0.)
• 🧪 Does the time from lifting the cloth to its turning blue change with temperature? (A continuous series of photographs could compare this.)
• 🧪 In a home indigo vat, how would zinc dust and sodium hydrosulfite compare in reducing power and in the finished dyeing?
• 🧪 If a Tyrian purple reduction bath is handled in the dark and in the light, does the final hue (how blue it is) really change?
• Why do the sources (Aizumi Town, Shikoku University, Kawahito 2015) differ so much on the number of turns ("kirikaeshi") and the weight of a bale of sukumo?
• When did the words "hon-ai" and "hon-ai-zome" first appear, and do they really come from a self-description by the Tokushima (Awa) producing region, as Riku Matsuzaki says?
• Does the Tanaka Nao Dyeing Materials Store's hydro discharge strip colour equally well at 60°C and at 80°C or above? (Within the store, the temperature and the companion agent are given differently from page to page.)