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Salty, cold, slightly toxic. Grows in ponds, marshes, and among grass and trees; its shape resembles a small snail, is white in color, and has four black horns on its head. Those that are round and large are superior; those that are small are unsuitable for use.

Acrid, neutral, toxic. For poisoning by it, only the meat of *Ardeola bacchus* (Chinese pond heron) can detoxify it. It is adverse to lead and fears mercury. In medical formularies, gold leaf (*Jinbo*, Gold Leaf) is described, but modern people do not know its actual size, relying merely on counts of pieces or sheets. Without personally viewing Tang dynasty standards, how could one know? Based on this, one qian of gold can be made into one thousand square-inch sheets.

Acrid, bitter. Found涩ly in copper mines and stone crevices; its shape and size are irregular, with a greenish-yellow color resembling copper. It does not undergo smelting, hence called "self-born." It is quenched nine times in vinegar over fire, ground into powder, and processed using the water-flying method (*Shuifei*, levigation) for use.

Acrid, sour, astringent, slightly toxic. The green substance found on copper vessels is taken, washed, and used. Recently, people have produced green copper by treating copper with vinegar, collecting and sun-drying it.

This is lead (*Qian*, Lead). Sweet, cold, slightly toxic. When used, it must be melted in an iron pot, poured onto tiles to filter out dregs, repeated several times, then collected for use. The residue from melting black tin ash is usable, but white tin ash is not used in medicine.

Sweet, acrid, cold. This is Hu Fen (Lead Carbonate), also commonly known as Guan Fen (Official Powder), made by processing lead. The method for making Hu Fen: Take 100 jin of lead, melt it, shave it into thin slices, roll them into tubes, and place them inside a wooden steamer (*Zeng*). Place a bottle of vinegar at the bottom and another inside the steamer. Seal the exterior with salt mud until... The remaining residue is left to be stir-fried into Huang Dan (Red Lead). Arrange the ash in trenches, separate with layers of paper, place the powder on top, and when nearly dry, cut into... All Hu Fen used in formulas is this substance. Currently, people call Hu Fen processed with clam ash via levigation "Hu Fen"; users should exercise caution.

Acrid, salty, cold. Processed by levigation, clarified, dried, and stir-fried over low heat until purple. Placed on the ground to remove fire toxicity before medicinal use. It can suppress arsenic and control cinnabar. Method for stir-frying Qian Dan (Lead Oxide): Use 1 jin of lead, 10 liang of sulfur, and 1 liang of saltpeter. Melt the lead into liquid, add vinegar drops; when boiling, add a piece of sulfur, then a little saltpeter after a short while. Once boiling subsides, mix with juice from scallions with roots, and slow-cook... For medicinal use, Guang Ming Dan (Bright Red Lead) is preferred. Those sold in markets with a earthy yellow color are improperly fried and should not be used.