colorant
Indigo (indigotin)
Also known as: indigotin
The blue colourant of indigo dyeing (indigotin). It does not dissolve in water: it is reduced to a water-soluble form (leuco-indigo), taken into the cloth, and oxidised in air back to blue.
Theme: Dissolve, then return
Claims and evidence (51)
The limitations noted for some sources are recorded in Japanese only — see the Japanese edition.
Indoxyl produces Indigo (indigotin)contextual
Scope: Under aerobic conditions
States that indoxyl is highly unstable and, on contact with air, is immediately oxidised and spontaneously, non-enzymatically polymerises into stable, insoluble indigo.
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
textbook ・ 
checked against the source by AIIndigo (indigotin) is insoluble in watercontextual
Scope: The source states only that indigo is "insoluble", without naming water as the solvent explicitly. The surrounding context (indigo forming as a precipitate) suggests insolubility in water, but this is not stated explicitly.
Describes the polymerisation product of indoxyl as “stable, insoluble indigo”.
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
Indigo (indigotin) ・found inAt least 31 species across eight plant families have been documented as indigo-yielding.contextual
States that 31 indigo-yielding species—annual and perennial herbs, shrubs, lianas and trees—across eight plant families have been documented, and that the true number is likely higher, as shown by the example of several indigo-yielding Isatis species alone.
Source: “Purplish Blue” or “Greenish Grey”? Indigo Qualities and Extraction Yields from Six Species （Anna Hartl; Andrea Polleichtner; Johannes Novak, 2024） ・§1.2 A Cornucopia of Species and Manufacturing Methods ・textbook ・ checked against the source by AI
Indigo (indigotin) ・propertyWhen cultivated and extracted in Austria, indigotin content varied greatly by species: Indigofera arrecta was highest at 55%, followed by Persicaria tinctoria (44%), Indigofera tinctoria (23%) and Indigofera suffruticosa (10%). Among species cultivated and extracted in China, Strobilanthes cusia was highest at 56%.supported
Scope: Measured with a standardised hot-extraction method (MME, without lime); Austria- and China-grown samples were compared separately
Reports indigotin content measured with a standardised extraction method (MME) for four species grown in Austria (Indigofera arrecta 55%, Persicaria tinctoria 44%, Indigofera tinctoria 23%, Indigofera suffruticosa 10%) and for Strobilanthes cusia grown in China (56%, statistically significantly higher than the other species tested there).
Source: “Purplish Blue” or “Greenish Grey”? Indigo Qualities and Extraction Yields from Six Species （Anna Hartl; Andrea Polleichtner; Johannes Novak, 2024） ・§2.1.1–2.1.2、Figure 2, Figure 4 ・experimental ・ checked against the source by AI
experimental ・ Indigo (indigotin) ・differenceThis source notes that the word “indigo” is used confusingly in at least four senses—(a) the plants used, (b) the extract as a traded product, (c) the valuable dyeing component, and (d) the colour blue itself—and states that in this article, “indigo” is used for the plant extract and “indigotin” for its valuable dyeing component.contextual
Scope: Terminology as defined in this source (Hartl et al. 2024)
Explains that “indigo” carries at least four meanings—(a) the plants, (b) the extract as a traded product, (c) the valuable dyeing component, (d) the colour blue—and that even the scientific literature conflates them; declares that in this article “indigo” denotes the plant extract and “indigotin” its valuable component, and notes that “indigotin” is also confusingly used for the synthetic food colourant E132.
Source: “Purplish Blue” or “Greenish Grey”? Indigo Qualities and Extraction Yields from Six Species （Anna Hartl; Andrea Polleichtner; Johannes Novak, 2024） ・§1.5 Definitions of Terms ・textbook ・ checked against the source by AI
Indigo (indigotin) is insoluble in watercontextual
States that indigo, the colorant of indigo dyeing, is a dye that does not dissolve in water.
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, 冒頭「藍を建てる」の段落 ・practitioner's record ・ checked against the source by AI
practitioner's record ・ States that indigo's disadvantage is that it is insoluble in water.
Source: Indigo （David Richardson; Sue Richardson, 2016） ・"The Natural Indigo Dyeing Process" 節 冒頭 ・textbook ・ checked against the source by AI
States that indigotin is insoluble in water, dilute alkalis and dilute acids, and that this gives it good wash-fastness.
Source: Indigo （David Richardson; Sue Richardson, 2016） ・"Physical and Chemical Properties of Indigotin" 節 ・textbook ・ checked against the source by AI
Leuco-indigo (reduced indigo, "indigo white") differs from Indigo (indigotin)contextual
Explains that indigo is reduced, taken up by cloth or thread, and then on oxidation reverts to indigo, dyeing it blue.
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
Captions a diagram stating that indigo is transformed into leucoindigo by the action of indigo-reducing bacteria.
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） ・Figure 1 のキャプション ・textbook ・ checked against the source by AI
Indigo (indigotin) works by reduction to a soluble form and re-oxidationcontextual
States that leuco-indigo, despite its pale yellow appearance, is also called "indigo-white," and that it is quickly oxidised on contact with air, changing to greenish-blue and finally blue.
Source: Indigo （David Richardson; Sue Richardson, 2016） ・"The Natural Indigo Dyeing Process" 節 ・textbook ・ checked against the source by AI
Describes that once slaked lime is dissolved in and the liquid is stirred, the indoxyl in the water loses hydrogen and oxidises, gradually producing blue indigo.
Source: 泥藍を作ろう（畑だより 2021年09月23日） （藍ばたけ（琉球藍染め）, 2021） ・本文中盤、消石灰を加えて攪拌する場面 ・practitioner's record ・ checked against the source by AI
The fermentation log notes that stirring raises a green foam, which re-oxidises and turns blue.
Source: 灰汁発酵建て（仕込み分量：1.5石（270ℓ）瓶建て） （四国大学 藍の家 研究室） ・「止石投入の頃」の発酵経過、6〜7日目 ・practitioner's record ・ checked against the source by AI
States reduction temporarily turns the dye from vivid blue to a very pale greenish-yellow colour, and that the dye starts to oxidise back to blue immediately on exposure to air.
Source: Denim Fabric Manufacturing (Technical Bulletin ISP 1010) （Cotton Incorporated, 2004） ・ISP 1010, "Rope Dyeing" 節、還元剤の段落 (pp.6-7) ・manufacturer statement ・ checked against the source by AI
manufacturer statement ・ Indigo (indigotin) bonds via Mechanical entrapment without covalent bondingcontextual
States that indigo precipitates on the surface of cotton fibres but does not chemically bond with the cellulose; it adheres by weak hydrogen bonding, meaning it can be removed by abrasion or repeated washing.
Source: Indigo （David Richardson; Sue Richardson, 2016） ・"The Natural Indigo Dyeing Process" 節、末尾の段落 ・textbook ・ checked against the source by AI
Indigo (indigotin) has the property of Ring dyeing (white core)contextual
States that when cotton fibres are dyed with indigo, only the outermost fibrils absorb the dye while the core stays white, with the dyed fibrils acting as a barrier that prevents the indigo penetrating further into the undyed part — a phenomenon called "ring dyeing."
Source: Indigo （David Richardson; Sue Richardson, 2016） ・"Ring Dyeing and Substantivity" 節 ・textbook ・ checked against the source by AI
Indigo (indigotin) ・requiresBuilding up a deep indigo colour is said to require repeated "dip and oxidise" cycles; the more times the cloth is dipped, the deeper the colour, though the gain becomes smaller each time. One study found the increase in depth slowing markedly after the eighth dip, with the colour cast shifting from greenish dark blue toward a redder, less blue tone as dips increased, and judged around ten dips to be optimal.contextual
Scope: Indigo dyeing of cotton, as cited in the source
States that because increased colour depth cannot be achieved by dye concentration alone, the number of dips is increased instead, but that after the eighth dip the gain in depth of shade slows markedly, and that as the number of dips increases there is a shift in colour cast from greenish dark blue to a redder, less blue tone; the optimum number of dips is judged to be about ten.
Source: Indigo （David Richardson; Sue Richardson, 2016） ・"Ring Dyeing and Substantivity" 節、末尾 ・textbook ・ checked against the source by AI
vat dye contains Indigo (indigotin)contextual
States that the colorant of indigo dye is indigo.
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
Context: States that the main colorant of indigo is indigotin, whose structure was reported by Adolf von Baeyer in 1883.
Source: Indigo （David Richardson; Sue Richardson, 2016） ・"Indigotin" 節 ・textbook ・ checked against the source by AI
Indigo (indigotin) ・propertyLists example supplementary wordings for indigo-dyed products: colour may transfer to other items through sweat or rubbing during wear; the colour will whiten with repeated washing; and the item should be washed separately because it bleeds colour when washedcontextual
Scope: Example wording for indigo-dyed products, per BOKEN's list
Lists the three example attention sentences specifically for indigo-dyed items, about sweat/rub transfer, whitening with washing, and the need to wash separately.
Source: 商品の特性情報（デメリット、商品説明や注意表示）を示す付記用語例 （一般財団法人ボーケン品質評価機構, 2017） ・「②素材別の付記用語」表の「インディゴ」の行 ・institutional summary ・ checked against the source by AI
institutional summary ・ Indigo (indigotin) ・propertyProvided the piece is washed thoroughly after dyeing, states vat-dyed indigo has wash fastness of grade 4-5, light fastness (UV carbon-arc) of grade 3-4, and dry rubbing fastness from grade 3 up to grade 5 depending on the item — markedly better than typical plant dyeing generallycontextual
Scope: Figures conditional on thorough post-dye washing, per this source's general account
Conditional on thorough post-dye washing, rates this dyeing type's fastness as very good, citing figures of wash 4-5, light (carbon-arc) 3-4, and dry rubbing 3-5, and stressing the gap versus ordinary plant dyeing.
Source: 染色・草木染めにおける堅牢度（けんろうど）。色落ちしづらく染めて、染色堅牢度を高める方法について （iroai.jp, 2026） ・「藍染と堅牢度」の段落 ・practitioner's record ・ checked against the source by AI
Indigo (indigotin) has the property of Ring dyeing (white core)contextual
Scope: Vat (fermentation-set etc.) indigo dyeing, per this source's general account
Names wet rubbing as the weak point, giving figures of roughly grade 2 for deep shades and 3-4 for pale ones, then contrasts how shade depth cuts both ways: darker is worse for rubbing but better for light fastness.
Source: 染色・草木染めにおける堅牢度（けんろうど）。色落ちしづらく染めて、染色堅牢度を高める方法について （iroai.jp, 2026） ・「藍染と堅牢度」の段落後半 ・practitioner's record ・ checked against the source by AI
Indigo (indigotin) produces Isatincontextual
Scope: The text says it is pale indigo shades that take on a yellowish tinge in sunlight; it does not discuss yellowing of deep shades
States that indigo on the cloth is oxidised by singlet oxygen, generated under UV light, into isatin; after the example that a drop of nitric acid turns it into yellow isatin by the same oxidation, says pale indigo shades likewise take on a yellowish tinge in sunlight, and that the influence of isatin is large as a reason why indigo-dyed cloth yellows. Also says extremely pale shades (kame-nozoki) can turn greenish with ageing, including the effect of sunlight, as the remaining indigo and the yellow isatin mix.
Source: 染色・草木染めにおける堅牢度（けんろうど）。色落ちしづらく染めて、染色堅牢度を高める方法について （iroai.jp, 2026） ・「藍染された布が黄色味を帯びる理由」 ・practitioner's record ・ checked against the source by AI
Isatin differs from Indigo (indigotin)contextual
States isatin is water-soluble, so washing basically removes the yellow tinge.
Source: 染色・草木染めにおける堅牢度（けんろうど）。色落ちしづらく染めて、染色堅牢度を高める方法について （iroai.jp, 2026） ・「藍染された布が黄色味を帯びる理由」末尾 ・practitioner's record ・ checked against the source by AI
Indigo (indigotin) ・attributed toStates that industrial research on indigo began with Baeyer's 1865 work at the Gewerbeinstitut, which found indole to be the parent substance of indigo, though at that point no source of indole other than the indigo plant itself could be found.contextual
Scope: Concerns the early industrial-research phase on indigo (Baeyer's work).
States that industrial indigo research started with Baeyer's 1865 Gewerbeinstitut work, which identified indole as indigo's parent substance — though at the time no source of indole besides the indigo plant itself was known.
Source: Plantation science: improving natural indigo in colonial India, 1860–1913 （Prakash Kumar, 2007） ・p.547「Industrial research on indigo began...」 ・textbook ・ checked against the source by AI
Indigo (indigotin) ・attributed toStates that BASF industrial chemist Heinrich Caro forged a collaboration with Baeyer, who managed to synthesise indigo using different pathways in 1878 and 1880; this success led to a tripartite research-and-development agreement between Baeyer, BASF and Hoechst.contextual
Scope: Concerns the c.1878-1880 collaboration among Baeyer, BASF and Hoechst.
States that the BASF industrial chemist Heinrich Caro forged a collaboration with Baeyer; benefiting from this partnership, Baeyer managed to synthesise indigo using different pathways in 1878 and 1880, igniting industrial interest and leading to a tripartite R&D agreement between Baeyer, BASF and Hoechst.
Source: Plantation science: improving natural indigo in colonial India, 1860–1913 （Prakash Kumar, 2007） ・p.547「The BASF industrial chemist Heinrich Caro...」 ・textbook ・ checked against the source by AI
Indigo (indigotin) ・attributed toStates that BASF took Baeyer's second (toluene-based) route to industrial scale, bringing out an 1880 intermediate that, once reduced, would fix indigo onto printed fabric — but that it failed to attract printers, partly because it was priced at twice that of natural indigo.contextual
Scope: Concerns an 1880 intermediate product that itself was a commercial failure; not yet full-scale supply of synthetic indigo dye itself.
States that BASF industrialised Baeyer's second (toluene-based) route, putting an intermediate on the market by 1880 that could, once reduced, fix indigo onto printed fabric — but that the product failed to win over printers, partly because it was priced at twice the level of natural indigo.
Source: Plantation science: improving natural indigo in colonial India, 1860–1913 （Prakash Kumar, 2007） ・p.547「The second Baeyer pathway...」 ・textbook ・ checked against the source by AI
Indigo (indigotin) ・attributed toStates that in 1890 Heumann (Zurich) established a synthesis pathway starting from naphthalene, derived from coal tar; BASF and Hoechst secured rights to use it, and after seven more years of industrial development, synthetic indigo reached the market in 1897 (BASF in July). The name is spelled "Carl Heumann" in one source and "Karl Heumann" in another.contextual
Scope: Concerns the path from establishing the industrial synthesis route to BASF's and Hoechst's market launch.
States that Carl Heumann of Zurich Polytechnic worked out a naphthalene-from-coal-tar route in 1890; BASF and Hoechst quickly bought rights to it, and seven more years of industrial development led to BASF's synthetic-indigo launch in July 1897, with Hoechst close behind.
Source: Plantation science: improving natural indigo in colonial India, 1860–1913 （Prakash Kumar, 2007） ・p.548「In 1890 Carl Heumann at Zurich Polytechnic...」 ・textbook ・ checked against the source by AI
States that a fresh contribution from Karl Heumann (as spelled in this source), a Zurich professor, in 1890 let BASF beat every competitor to market with "Indigo pure BASF" in 1897.
Source: Cooperative Research — Formula for Success （BASF SE） ・本文「New impetus form outside is received from Karl Heumann...」 ・manufacturer statement ・ checked against the source by AI
Indigo (indigotin) ・propertyStates that between 1880 and 1896 the average annual value of world output of plant-derived indigo was estimated at 80 million marks, equal to the combined turnover of all European coal-tar dye factories (citing Reinhardt and Travis).contextual
States, citing Reinhardt and Travis (2000), that plant-derived indigo's average annual world output value from 1880-1896 — 80 million marks — matched the combined revenue of every European coal-tar dye factory.
Source: Plantation science: improving natural indigo in colonial India, 1860–1913 （Prakash Kumar, 2007） ・p.547「between 1880 and 1896 the average annual value...」 ・textbook ・ checked against the source by AI
Indigo (indigotin) ・causesStates that cheaper, purer German synthetic indigo, launched in 1897, rapidly ate into demand for natural indigo—first in Germany, then in British, French and American markets—and that total exports from Calcutta (which mainly shipped Bihar indigo) "plummeted"; per Table 2, export weight from Calcutta fell from 111,714 cwt in 1895-6 to 19,062 cwt in 1905-6, to less than a fifth of the 1895-6 total within a decade.contextual
States that after synthetic indigo's 1897 appearance, natural-indigo demand was rapidly eaten into first in the German then the British, French and American markets, and that total exports from Calcutta plummeted; Table 2 shows a fall from 111,714 cwt (1895-6) to 19,062 cwt (1905-6), to under a fifth of the 1895-6 total within a decade.
Source: Plantation science: improving natural indigo in colonial India, 1860–1913 （Prakash Kumar, 2007） ・p.548 本文とTable 2 ・textbook ・ checked against the source by AI
Indigo (indigotin) ・differenceStates that most Western cotton printers quickly switched to synthetic indigo for its purity, and natural indigo never won back this market segment; but niche demand persisted (e.g. woollen dyeing, for technical reasons), and some dyers mixed a small amount of natural (Bengal) indigo into synthetic indigo to improve fastness or obtain a distinctive coppery-red tinge.contextual
States that most Western cotton printers quickly switched to synthetic indigo, showing a strong preference for its purity, and that natural indigo never won back this segment of "purity-conscious" consumers; it notes niche demand such as woollen dyeing (for technical reasons) and dyers who mixed a little Bengal indigo with synthetic indigo to improve fastness or obtain a coppery-red tinge.
Source: Plantation science: improving natural indigo in colonial India, 1860–1913 （Prakash Kumar, 2007） ・p.556「Most Western cotton printers quickly switched...」 ・textbook ・ checked against the source by AI
Indigofera suffruticosa produces Indigo (indigotin)supported
Scope: A comparative cultivation study in Sakon Nakhon Province (May-Sep 2023, RCBD, 4 plots per treatment). Note: for the light-condition comparison, the source's own discussion text right after Table 3 contains a sentence stating the opposite (that I. tinctoria was higher), while the abstract, conclusion and Table 3's own numbers all agree that I. suffruticosa was higher (apparently an internal inconsistency in the source itself).
Tables 1-3 show Indigofera suffruticosa's YIBL (indigo blue yield per fresh leaf weight) higher than I. tinctoria across pod stage, harvest time and light conditions, with ANOVA showing p < 0.05 significance.
Source: Effects of Cultivation Factors on Indigo Dye Yield in Indigofera Plants （Witchapol Thosaikham, Pornkamon Sakong, 2024） ・p.4-7, Results and discussion, Tables 1-3 ・experimental ・ checked against the source by AI
Indigo (indigotin) ・requiresIndigo-dyed threads tended to show elevated calcium; the authors suggest this may reflect use of a calcium source (such as burnt shell) to alkalise the indigo vat.preliminary
Scope: The indigo-dyed threads among those mapped by XRF that showed elevated calcium.
Calcium turned up in every thread, reaching its peak in two black cotton threads coloured with an indigo dye (from Indigofera or Cybistax) combined with a yellow, and its lowest levels in most red threads and undyed cotton. The authors propose calcium may likewise have served as a dyeing auxiliary, and that its being elevated in strongly indigoid threads could point to a calcium source, such as burnt shell, used to alkalise the vat.
Source: Revealing the organic dye and mordant composition of Paracas textiles by a combined analytical approach （Francesca Sabatini; Martina Bacigalupo; Ilaria Degano; Anna Javér; Marei Hacke, 2020） ・Results and discussion > Analysis of the inorganic components ・analytical ・ checked against the source by AI
analytical ・ Indigo (indigotin) ・found inThis blog post (Andean Textile Arts) states that the oldest surviving example of indigo-dyed cloth is Peruvian in origin and reportedly more than 6,000 years old.contextual
Context: In previewing upcoming colour topics, the post mentions indigo, asking readers whether they know that the oldest surviving sample of indigo-dyed cloth is said to be Peruvian and dates back more than 6,000 years.
Source: Andean Natural Dyes: Practical, Deep, and Empowering （Ercil Howard-Wroth, 2020） ・本文「The Andean Color Story」の段落 ・journalistic report ・ checked against the source by AI
journalistic report ・ 6,6'-Dibromoindigo (Tyrian purple) differs from Indigo (indigotin)contextual
Refers to the structure as 6,6'-dibromoindigo and states Friedländer identified it in 1909, distinguishing it from unbrominated indigo by that bromine substitution.
Source: Preparation of Tyrian Purple (6,6'-Dibromoindigo): Past and Present （Christopher J. Cooksey, 2010） ・Introduction 第1段落 ・textbook ・ checked against the source by AI
Explains that the pigment's substance is an organic compound called dibromoindigo, which contains bromine among its constituent elements.
Source: ジブロモインジゴ dibromoindigo （Chem-Station（投稿者: Green）, 2012） ・記事本文、色素の説明の段落 ・textbook ・ checked against the source by AI
Indigo (indigotin) ・used inThis record states that in Cambodian silk ikat indigo was used for blue, alongside bror hut bark for yellow, lac for red and mok clua for blackcontextual
Scope: A 1996 record; the same paragraph adds that most dyeing today uses chemical dyes
Lists indigo for blue and mok clua (ebony fruit) for black among the colours used, adding that most dyeing today is chemical.
Source: Traditional Natural Dyes in Cambodian Ikat Weaving （Katharine Wardle（Khemara プロジェクト）, 1996） ・本文「Other colors used included indigo for blue」の文 ・practitioner's record ・ checked against the source by AI
Indigo (indigotin) ・found inIndigo is said to have also been used to dye the ivory fittings of a small knife, 'Ryokuge Bachiru no Tsuka Saya Onto-su', once owned by Emperor Shomu, revealing that plant dyes were used broadly even on crafts other than textiles.preliminary
Scope: The ivory fittings of a small knife owned by Emperor Shomu
States indigo was also used to dye the ivory fittings of a knife owned by Emperor Shomu, showing plant dyes were used broadly beyond textiles.
Source: 正倉院染織品に使われた植物染料の材質分析（非破壊手法による分析で1,250年前の染料を特定する） （中村力也, 2010） ・p.747 本文末尾 ・analytical ・ checked against the source by AI
Indigo (indigotin) ・found inAll the blue-colored areas analyzed (the bodies of the sutra wrapper for Shōjō-zakkyō and sutra wrapper No.1, the body and hem of sutra wrapper No.3, among others) are said to have shown a reflectance spectrum characteristic of indigo (ai), showing that indigo had been used.preliminary
Scope: All blue-colored areas of the Shosoin sutra wrappers analyzed
States all analyzed blue-colored areas showed a reflectance spectrum characteristic of indigo.
Source: 分光学的手法による正倉院に伝世する竹帙の色糸に用いられた染料の分析 （中村力也・成瀬正和） ・p.28-29「3.2 青色系統」 ・analytical ・ checked against the source by AI
Indigo (indigotin) ・used inThe green-colored areas, such as the body of sutra wrapper No.3 (g4, g5), are said to have shown indigo by visible spectroscopy and Amur cork tree by fluorescence spectroscopy, showing that the green was produced by over-dyeing indigo with Amur cork tree.preliminary
Scope: The green-colored areas of the Shosoin sutra wrappers analyzed
States the green areas (g4, g5) of the body of sutra wrapper No.3 showed an indigo-characteristic visible spectrum and Amur-cork-tree fluorescence peaks, indicating over-dyeing of indigo with Amur cork tree.
Source: 分光学的手法による正倉院に伝世する竹帙の色糸に用いられた染料の分析 （中村力也・成瀬正和） ・p.32-33「3.4 緑色系統」 ・analytical ・ checked against the source by AI
Indigo (indigotin) ・propertyThis dye workshop states that even properly-dyed indigo products retain some dye that the fibre could not absorb, so colour initially transfers onto clothing or skin (though it washes off with soap); repeated washing and drying settles the colour, but settling is said to take many years.contextual
Scope: Regarding Mizuno Dye Works' indigo products (traditional vat-dyed)
States that even with the honzome technique properly applied there is a limit to how much dye the fibre can absorb, and the excess unabsorbed dye rubs off; repeating washing and drying settles the colour but this takes many years, so at first it may transfer to clothes or skin, though it comes off easily with soap.
Source: 藍染は色落ちする？洗濯・お手入れの仕方 （水野染工場, 2021） ・藍染は色落ちする？ ・manufacturer statement ・ checked against the source by AI
Indigo (indigotin) ・propertyThis dye workshop states there is no way to stop indigo colour loss outright, but thoroughly washing out the dye that failed to fix helps the colour settle and stabilise; it also states that storing an item in the dark for one to two years causes the indigo to 'harden' and stop rubbing off, without explaining what this hardening means chemically.contextual
Scope: Regarding Mizuno Dye Works' indigo products
States colour loss cannot be stopped, but thoroughly removing what can be removed helps the colour settle and stabilise, and that shade-drying/storing in the dark for one to two years causes the indigo to harden and stop rubbing off.
Source: 藍染は色落ちする？洗濯・お手入れの仕方 （水野染工場, 2021） ・藍染の色落ちを止める方法は？ ・manufacturer statement ・ checked against the source by AI
Indigo (indigotin) ・mechanismAs a remedy when indigo colour has transferred onto another item, this dye workshop gives the procedure: soak the affected item in lukewarm water with a mild-alkaline detergent and bleach added for 30 minutes to an hour, rinse once the colour has lifted, then do a normal wash.contextual
Instructs putting a mild-alkaline detergent plus bleach into lukewarm water, soaking for 30 minutes to an hour, rinsing once the colour has lifted, then doing a normal wash.
Source: 藍染は色落ちする？洗濯・お手入れの仕方 （水野染工場, 2021） ・藍染が色落ちして他のものに色移りしてしまったら ・manufacturer statement ・ checked against the source by AI
Indigo (indigotin) ・requiresFor home laundering of indigo products, this dye workshop gives the procedure: put a neutral detergent in lukewarm water, press-wash it, rinse by press-washing again in lukewarm water, optionally use fabric softener, and shade-dry in a well-ventilated spot; it also advises not washing it with other items, not rubbing hard, storing away from light, and ironing from the reverse side.contextual
Gives the steps: put neutral detergent in lukewarm water, press-wash, rinse by press-washing in lukewarm water again, optionally use fabric softener, and shade-dry somewhere well-ventilated; lists as cautions not washing with other items, press-washing gently rather than rubbing hard, storing away from light, and ironing from the reverse side.
Source: 藍染は色落ちする？洗濯・お手入れの仕方 （水野染工場, 2021） ・藍染製品の洗濯・お手入れ方法 ・manufacturer statement ・ checked against the source by AI
Indigo (indigotin) ・mechanismContinuing, Berthollet states that this alkaline solution of indigo decomposes on contact with the atmosphere, and the indigo recombines with the oxygen it draws from the air, returning to its natural (blue) state. He explains that when a fabric is dyed in an indigo vat it takes on a green colour, but turns blue as soon as it is exposed to air, because the indigo recombines with oxygen drawn from the atmosphere, while the alkali or lime is carried off by washing.contextual
Scope: The theory of the indigo vat, on the change from green to blue.
Explains that fabric dyed in an indigo vat turns green, but becomes blue on air exposure because 'l'indigo se recombine avec l'oxygène qu'il attire de l'atmosphère' (the indigo recombines with the oxygen it draws from the atmosphere).
Source: Éléments de l'art de la teinture. Volume 2 （Berthollet, Claude-Louis (1748-1822), 1791） ・第2巻 第2部 第2節 第1章 (藍のアルカリ溶液の分解についての一節) ・historical record ・ checked against the source by AI
historical record ・ Alizarin is found in Indigo (indigotin)contextual
Scope: 3 of the 7 samples analysed from this one Coptic tapestry.
Absorption maxima of alizarin/purpurin and of indigotin were detected simultaneously in samples 1, 5 and 6, described as 'a mixture of madder and woad dye'.
Source: Identification of natural dyes in rare Coptic textile using HPLC-DAD and mass spectroscopy in museum of Faculty of Arts, Alexandria University, Egypt （Harby E. Ahmed; Ibrahim F. Tahoun; Ibrahim Elkholy; Adel B. Shehata; Yassin Ziddan, 2017） ・p.488-490 §4.1.1・§4.1.5・§4.1.6、Table 2 ・analytical ・ checked against the source by AI
Indigo (indigotin) ・found inIn sample 4 (a blue-toned area) of the same Coptic tapestry, only indigotin and indirubin were detected, with no alizarin or purpurin (madder) found.contextual
Scope: This one sample (No.4) from this single Coptic tapestry only.
Sample 4 showed only indigotin (RT 31.49 min, 242/285/330/610 nm) and indirubin (RT 33.23 min, 239/290/363/542 nm), classified as woad dye alone.
Source: Identification of natural dyes in rare Coptic textile using HPLC-DAD and mass spectroscopy in museum of Faculty of Arts, Alexandria University, Egypt （Harby E. Ahmed; Ibrahim F. Tahoun; Ibrahim Elkholy; Adel B. Shehata; Yassin Ziddan, 2017） ・p.488 §4.1.4 Sample No. 4、p.490 Table 2 ・analytical ・ checked against the source by AI
Indigo (indigotin) is attributed to Woadcontextual
Scope: The paper's own general background statement, not specific to Egypt.
Context: States Indigofera tinctoria had, by the mid-17th century, almost completely replaced European woad, and both lost importance after synthetic indigo's introduction in 1882.
Source: Identification of natural dyes in rare Coptic textile using HPLC-DAD and mass spectroscopy in museum of Faculty of Arts, Alexandria University, Egypt （Harby E. Ahmed; Ibrahim F. Tahoun; Ibrahim Elkholy; Adel B. Shehata; Yassin Ziddan, 2017） ・p.488 §4.1.1本文 ・textbook ・ checked against the source by AI
Indigo (indigotin) is found in Flax (linen fibre)contextual
Scope: The blue area of this one linen fragment from Tutankhamun's tomb.
SERS spectra of the gel extract from the blue area showed characteristic peaks of indigotin (1073, 1176, 1369, 1470 cm-1) and indirubin (645, 971, 1404, 1585 cm-1), with the latter more intense, probably due to thermal degradation of the dye.
Source: Applying Gel-Supported Liquid Extraction to Tutankhamun's Textiles for the Identification of Ancient Colorants: A Case Study （Greta Peruzzi; Alessandro Ciccola; Adele Bosi; Ilaria Serafini; Martina Negozio; Nagmeldeen Morshed Hamza; Claudia Moricca; Laura Sadori; Gabriele Favero; Valentina Nigro; Paolo Postorino; Roberta Curini, 2023） ・§2.2.3 Surface Enhanced Raman Scattering (SERS) ・analytical ・ checked against the source by AI
Indigo (indigotin) ・propertyPer the article, India and El Salvador are described as the two biggest producers of natural indigo; the market also has cheap chemical indigo and natural indigo "impure"/adulterated with synthetic dyes. The article quotes Ahmad as saying many dyers use adulterated dye while calling it natural indigo, knowingly or not.contextual
States India and El Salvador are the two biggest natural-indigo producers and that cheap chemical indigo and synthetic-adulterated "impure" indigo also circulate, followed by Ahmad's quoted remark that many dyers use adulterated dye under the "natural indigo" name, knowingly or not.
Source: Local indigo goes global （Sohel Parvez, 2018） ・記事後半(『India and El Salvador are the two biggest producers...』の段落と直後の引用) ・journalistic report ・ checked against the source by AI
Indigo (indigotin) ・why it fell out of useThis article states natural indigo first displaced woad almost completely by the end of the 17th century, driven by growing indigo production in India paired with industrialisation-driven demand in Europe, but the synthesis of indigo by German chemist Adolf von Baeyer and the start of commercial production in 1897 then caused both woad and global natural-indigo cultivation to collapse.contextual
States indigo nearly displaced woad by the end of the 17th century, and that Baeyer's synthesis plus commercial production from 1897 collapsed both woad and natural indigo cultivation.
Source: Blueprint - Resist Block Printing and Indigo Dyeing in Europe （Karin Altmann） ・本文冒頭「In the temperate zones of Europe, woad...」の段落 ・journalistic report ・ checked against the source by AI
Indigo (indigotin) causes Ring dyeing (white core)contextual
States indigo is unique among major textile dyes for its very low affinity for cotton fibre, so the ball-warp dyeing process ring-dyes the cotton; with almost any other dye this outcome would be considered a defect.
Source: Denim Fabric Manufacturing (Technical Bulletin ISP 1010) （Cotton Incorporated, 2004） ・ISP 1010, "Rope Dyeing" 節冒頭 (p.6) ・manufacturer statement ・ checked against the source by AI
sulfur dye differs from Indigo (indigotin)contextual
Scope: Comparison of ozone-treated pure-indigo and indigo/sulfur-mixed denim
States the three fabrics dyed with indigo/sulfur mixtures (Fabrics 6-8) responded less to ozone than the five indigo-only fabrics, and speculates this is because sulfur dyes' sulfur-linkage-based chemical structure is less susceptible than indigo's carbon-carbon double bond to ozone cleavage.
Source: Finishing of denim fabrics with ozone in water （Taina Kamppuri; Shahriare Mahmood, 2019） ・Results and discussion > "Effect of ozone on color of water samples" および Conclusion ・experimental ・ checked against the source by AI
Indigo (indigotin) produces Isatincontextual
States ozone cleavage of indigo's chemical structure yields isatin, citing the treated water's UV-Vis spectrum following that of a reference isatin sample as evidence.
Source: Finishing of denim fabrics with ozone in water （Taina Kamppuri; Shahriare Mahmood, 2019） ・Results and discussion > "Effect of ozone on color of water samples" 節 ・experimental ・ checked against the source by AI
Kubovaya naboyka (Russian indigo vat-dye resist block printing) requires Indigo (indigotin)contextual
States indigo was imported via Arkhangelsk from the mid-17th century, with Moscow offering the best prices by 1900 (remote areas could be over double).
Source: Технология ручной кубовой набойки XIX-начала XX вв. на территории Владимирской области （В. Королькова (Живая нить традиций. Владимирская область / Традиции33)） ・「Индиго в больших количествах завозился в Россию через Архангельский порт...」の段落 ・institutional summary ・ checked against the source by AI
Indigo (indigotin) produces Isatincontextual
Scope: Yellowing of indigo-dyed fabric (denim etc.) during storage
States the symptom was an indigo-dyed shirt yellowing during storage; states that indigo-dyed fabric can yellow in some cases because of three factors: residue from the decomposition of bleach agent (sodium hypochlorite), oxidative decomposition by UV light, and the action of atmospheric nitrogen oxides (NOx). Says these influences decompose the indigo dye to form isatin, which causes the yellowing.
Source: No463_より良いモノづくりのために 染色・プリントの事故事例 -イサチン黄変- （一般財団法人ボーケン品質評価機構, 2025） ・「現象」「原因」 ・institutional summary ・ checked against the source by AI
Isatin differs from Indigo (indigotin)contextual
As a supplementary note, states isatin is water-soluble and removable by washing, but because it forms from decomposition of the indigo dye, the washed colour ends up paler than the original.
Source: No463_より良いモノづくりのために 染色・プリントの事故事例 -イサチン黄変- （一般財団法人ボーケン品質評価機構, 2025） ・「補足」 ・institutional summary ・ checked against the source by AI
Indigo (indigotin) is applicable to Chemical reduction of indigo (chemical vat)contextual
Scope: Maiwa's general explanation of indigo vats
Breaks every indigo vat down into just three ingredients — the pigment, something to reduce it, and something alkaline — and lists sugars, certain natural dyestuffs or plant matter, and chemicals as the options for that middle, reducing role.
Source: Indigo — Natural Dyes （Maiwa） ・"HOW TO DYE WITH INDIGO"、"All indigo vats need three things"の一文と"A reducing agent"の項 ・manufacturer statement ・ checked against the source by AI
Indigotine / Indigo Carmine (Food Blue No. 2) differs from Indigo (indigotin)contextual
States it is made by sulfonating indigo, implying it is a water-soluble derivative distinct from insoluble indigo itself.
Source: 食用色素の化学 （片山脩, 1974） ・誌面623頁「V. インジゴイド系食用色素」の項 ・textbook ・ checked against the source by AI
Open questions (3)
What change does 'the indigo hardens and stops rubbing off' after 1-2 years of dark storage actually refer to?🧪 testable at home
Mizuno Dye Works states that storing indigo-dyed goods in the dark for 1-2 years makes the indigo 'harden' and stop rubbing off, without explaining what change this refers to chemically. Could two swatches of the same indigo-dyed cloth be compared, one stored long-term in the dark and one in normal use, with a simple wet-white-cloth rub test every six months or year to compare how much colour transfers?
Is the strong SERS signal (1037 cm-1) seen in the blue area of the Tutankhamun linen fragment due to anthranilic acid, an indigo degradation product?
The authors themselves state this assignment is only a hypothesis and that further analysis (e.g. HPLC/MS) is needed to confirm the presence of this compound.
Does the time it takes for fabric lifted from an indigo vat to turn blue change with air or vat temperature?🧪 testable at home
Sources say reduced indigo (yellow to yellow-green) turns blue via green on exposure to air, but no source in our records relates the time taken to temperature. Could be compared with timed photos.