Qingdai, also known as indigo flower or indigo powder, is a dried powder or lump made from the leaves or stems of the familiy Acanthaceae plant Baphicacanthus cusia (Nees) Bremek., the Polygonaceae plant Polygonum tinctorium Ait., or the Brassicaceae plant Isatis indigotica Fort. It mainly contains indigo blue (indigo). The stems and leaves are harvested in summer and autumn, soaked in water for 2-3 days until the leaves rot and the stems peel off. The stems are then removed, lime is added (8-10kg per 100kg of material), and thoroughly mixed until the soaking liquid changes from dark green to purple-red. The foam-like substance on the liquid surface is scooped out and dried in the sun.
[Processing method] "Grind finely" according to "Taiping Shenghui Fang". "Remove the ash and soil" according to "Zhengzhi Zhunzheng". "Now only use indigo flower, but dried indigo is often mixed with lime, so it needs to be washed and clarified, and only the floating part is used" according to "Bencao Tongxuan". "Water flies away, but lime is present. It is better to wash and use it in medicinal paste" according to "Paozhi Da Fa". "Boil it with boiling water, filter out the coarse residue with a gauze sieve placed on a rice cooker, and repeat the process four or five times to extract and clarify it, then dry it in the sun" according to "Zengguang Yanfang Xinbian". Currently, the original medicinal material is taken, impurities are removed, and it is finely ground and sieved through an 80-mesh sieve.
[Characteristics of the herbal piece] It is a dark blue powder, light in weight, and easily disperses in the air. It can also be in the form of irregular porous lumps, which can be easily crushed into fine powder by hand. It has a slight grassy smell and a mild taste.
[Quality requirements] Take 0.5g of the product, add 10ml of water, shake it and let it stand for a while. The water layer should not show a deep blue color (checking water-soluble pigments). The product should contain not less than 2.0% indigo blue (C16H10N2O2).
[Processing effects] Qingdai has a cold and bitter taste and belongs to the liver meridian. It has the functions of clearing heat and detoxifying, cooling blood, and calming tremors. After being processed and pulverized, it is used for treating heat-induced rashes, blood heat vomiting nosebleeds, chest pain and coughing blood, mouth ulcers, mumps, throat obstruction, and childhood epilepsy. For example, the Qingdai drink is used to treat dissipating rashes in cases of warmth disease or typhoid fever transforming into heat, where pathogenic factors enter the nutrient division, causing persistent fever and skin rashes (from "Shanghan Liushi"). The Fudian powder is used to treat hydrocephalus with neck swelling and swollen cheeks (from "Huizhitang Jingyan Fang"). The Green Robe powder is used to treat oral ulcers (from "Guoyao Zongzhi"). The Qinglianqing and Lixiaosan are used to treat rampant tooth decay (from "Yizong Jinjian"). The Qingdai detoxification pill is used to treat sore throat and throat pain caused by upward attack of heat toxin (from "Renzhai Zhizhi Fang"). The Qingdai pill is used to treat childhood epilepsy (from "Taiping Shenghui Fang"). Processing improves the cleanliness of the medicine, facilitates the dissolution of active ingredients, and is convenient for compounding and formulation.
