Loha patra, the black iron pot, is not nostalgia. It is a slow chemical conversation between the vessel and the herbs.
In the kitchens of north India, hair oils have been simmered in cast-iron vessels for as long as anyone can remember. The technique has a name in the classical texts — kshara taila paka, the long, slow paka of an oil that ends up the colour of wet earth.
When amla, bhringraj and methi are reduced in iron, a small amount of the metal leaches into the oil as ferrous compounds and binds with tannins from the fruit. This is what blackens the oil and what gave traditional bhringraj tailam its name — kesharanjana, literally "that which colours the hair." The chemistry is the same that turns iron-gall ink black on parchment.
Nothing about this is a substitute for a doctor. But there is a reason your grandmother insisted on the iron pot and refused the steel one. She was, in her quiet way, doing organic chemistry.
