An alkali (calcium hydroxide) that dissolves only sparingly in water. Because it dissolves slowly and keeps the liquid alkaline, it is used in indigo vats and in making mud indigo; it is also said to have been used since early times as a mordant in dyeing.
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Slaked lime (calcium hydroxide) differs from Sodium hydroxidecontextual
Scope: Managing alkalinity in the ash-lye fermentation vat
States that slaked lime does not dissolve readily in water and so has lasting effect, whereas sodium hydroxide dissolves readily and lacks lasting effect; when pH keeps dropping sharply, the fast-acting sodium hydroxide is used, but slaked lime and ash lye are the normal choice.
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-287,「管理する難しさ」の段落 ・practitioner's record ・ checked against the source by AI
Scope: Making doro-ai (mud indigo) from Ryukyu-ai in Okinawa, as recorded in one workshop
Describes soaking harvested Ryukyu-ai in water with a weight on top and waiting for fermentation to break down indican, releasing indoxyl into the water; once the timing looks right, the leaves are removed and slaked lime is dissolved little by little into the resulting yellow-green water while stirring continuously, oxidising the indoxyl into indigo; left to stand, the liquid separates into a clear layer and a precipitate, and the collected precipitate is the doro-ai.
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） ・本文前半〜中盤、収穫から消石灰投入までの描写 ・practitioner's record ・ checked against the source by AI
Slaked lime (calcium hydroxide) ・used inStates that lime (slaked lime) has long been used not only as a plaster material but also as a dye mordant.contextual
Scope: Traditional Japanese dyeing, per this column
States that lime obtained by processing limestone (not explicitly specified in this passage as slaked lime) has long been used as a dye mordant as well as a wall material (i.e. shikkui/plaster).
Source: 灰汁（あく）なき探求 （中島志保（奈良文化財研究所 埋蔵文化財センター アソシエイトフェロー）, 2016） ・本文第3段落 ・historical record ・ checked against the source by AI
States that the lime is made by burning oyster or clam shells in a wood fire above 1000°C, sealing them airtight in a jar while heat remains, and using the oxidised powder.
Source: 한국 전통 쪽염색방법 (韓国伝統藍染め方法) （정관채 (중요무형문화재 제115호 염색장 보유자), 2008） ・「1) 매염재 만들기 (1) 소석회 만들기」節 ・practitioner's record ・ checked against the source by AI
Slaked lime (calcium hydroxide) ・used inIn this interview article, inheritor Wang Jianxiong explains that the quality of the indigo mud depends on getting the proportion of lime right, and that practitioners judge it by tasting the saltiness of the indigo liquor and by the colour of the indigo froth (a peach-blossom colour indicating top quality).contextual
Scope: Zhenfeng County (Bouyei)
Quotes Wang Jianxiong: judging indigo-mud quality hinges on the lime proportion, checked by tasting the liquor's saltiness and by the froth colour (peach-blossom = top grade).
Source: “发现非遗之美”：布依族蓝靛染 （袁艳（収集整理）） ・「精心染出斑斓色彩」節 ・journalistic report ・ checked against the source by AI
Open questions (1)
Adding a lot of slaked lime at once is said to affect the indigo colour badly — has this actually been chemically verified?🧪 testable at home
The jstage article states that slaked lime is added gradually across shikomi, nakaishi and tomeishi because adding it all at once is said to cause an excess that affects the indigo colour, but the article itself says it is unclear whether how this affects the colour has ever been scientifically examined.
practitioner's record ・ 
checked against the source by AI
historical record ・ 
journalistic report ・