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Persian Qingdai (Indigo Naturalis) is the indigo flower from foreign lands. Since it is difficult to obtain, Chinese indigo flowers can also be used. (Li Shizhen)

The shape of true Qingdai differs from that of indigo flowers. Currently, because true Qingdai is rare and the efficacy of indigo flowers is similar, its name is borrowed for convenience. After rapid harvesting and sun-drying, the color is very purple-green. Market vendors often use dried indigo paste to pass off as Qingdai. However, dried indigo is withered, black, heavy, and solid, whereas indigo flowers are tender and light; they are also easy to distinguish. (Pharmacopoeia on Processing Medicinal Substances)

It tastes salty and sweet, has a neutral nature, and is cold in qi. It specifically treats pediatric gan accumulation with erosion, emaciation, fever, gan dysentery, kills gan parasites, and addresses pediatric erysipelas (Dan Du). It resolves various heat-induced convulsions and epilepsy. It can collect stagnant fire in the five zang organs, resolve heat toxins, drain liver fire, and eliminate food stagnation. (Zhu Zhenheng)

Generally, it treats liver heat and resolves lung and stomach heat.

Medical texts record its use for middle and lower jiao disorders and hernias. A woman suffered from wet sores all over her abdomen below the navel, extending to both yin organs, resembling "horse melon sores." They were itchy and painful, exuding yellow fluid, with no other lesions elsewhere. Her urination and defecation were obstructed, and her appetite decreased. Her face and body were slightly swollen. The physician treated it as a malignant sore, applying remedies containing eel, pine resin, and red lead, which intensified the heat and pain. Upon inquiry, it was learned that she loved alcohol and enjoyed eating fish, crabs, and other "wind-inducing" foods. She was urgently instructed to wash off the applied medicine. Four taels of purslane (Portulaca oleracea) were mashed, mixed with one tael of Qingdai, and evenly applied. The heat immediately subsided, and pain and itching ceased. Thereafter, Bazheng San (Eight-Ingredient Decoction for Rectifying the Righteous) was administered three times daily to dissipate external heat. As the dressing dried, it was replaced. Gradually reducing the dosage, she recovered in twenty days. This was likely due to the accumulation of wind-heat toxins in the middle and lower jiao. If not expelled, it might develop into intestinal abscess or internal hemorrhoids. Alcohol, sexual activity, and wind-inducing foods must still be strictly avoided. (Chen Cangqi)

Born from the yin-cold qi of water and earth, and enriched by the dense qi of earth, its nature and taste are salty, cold, sweet, and neutral, specializing in resolving heat toxins. (Miao Xiong)

For heat-pain in the heart and epigastrium, mix one qian of Qingdai with ginger juice and take orally. For hemoptysis due to lung heat, take one liang of Qingdai and one liang of Almond Seed (Xingren), stir-fried with Oyster Shell powder. Grind them together uniformly, mix with yellow beeswax, and form thirty pills. Take one pill per dose, sandwiched between half a dried persimmon, wrapped in wet paper, roasted until fragrant, chewed, and swallowed with congee broth. Administer three times daily.

[Discussion] The stems and leaves of herbs and trees are invariably green, yet this substance alone demonstrates specific utility. Indigo plants sprout between spring and summer and bear fruit in the fifth and sixth lunar months. The term "collect" refers to gathering the qi of fire pathogens. Unlike the dispersing and draining actions of Cyperi Rhizoma (Xiangfu) and Tangerine Peel (Qingpi), it greatly disseminates the qi of generating yang to facilitate movement. Why is it an accurate agent for detoxification? Because when righteous qi flows smoothly, pathogenic qi naturally dissipates. Why is it more frequently used for conditions related to heavenly qi in the upper half of the body? Because this is precisely the sign of generating qi transforming and ascending to heaven. Furthermore, why is it most effective at killing insects? Because it transforms dampness into water and uses generating yang qi to move stagnant blood. Additionally, regarding Indigo: Directly using indigo juice or Isatidis Radix (Banlangen) from the chest down to the Heart Meridian killed a spider. Adding musk and realgar to indigo juice and injecting another spider caused it to dissolve into water. Thus, taking its juice for topical application... serves as evidence.

Qingdai treats excess heat in the blood level. However, if vomiting blood, epistaxis, or spitting blood results from yin deficiency with yang hyperactivity, where fire flares upward due to emptiness, this herb is not the precise对症 agent.

[Processing] Only take the portion floating in the sedimentation vat, dry it in the sun. When used, remove the bottom sediment via water levigation (flying method) because it contains lime (calcined stone); it should be levigated cleanly before oral administration. For external application...