India ink (or Indian ink in British English) is a simple black ink once widely used for writing and printing and now more commonly used for drawing, especially when inking comic books and comic strips. Indian ink is also used in medical research and is considered a suitable material for demonstration of the blood vessels under the microscope.
Basic India ink is composed of a variety of fine soot known as lampblack, combined with water to form a liquid. A binding agent such as gelatin or, more commonly, shellac may be added to make the ink more durable once dried. India ink is occasionally sold in solid form (most commonly, a stick), which must be moistened before use.
The process of making India ink was known in China as far back as the middle of the 3rd millennium BC, during Neolithic China. India ink was first invented in China, although the source of materials to make the carbon pigment in India ink was later often traded from India, thus the term India ink was coined. The traditional Chinese method of making the ink was to grind a mixture of hide glue, carbon black, lampblack, and bone black pigment with a pestle and mortar before pouring it into a ceramic dish where it could dry. In order to use the dry mixture, a wet brush would be applied until it reliquified. The manufacture of India ink was well-established by the Cao Wei Dynasty (220–265 AD). Historically the ink used in China were in the form of ink sticks made of lampblack and animal glue.
The Chinese had used India ink derived from pine soot prior to the 11th century AD, when the polymath official Shen Kuo (1031–1095) of the mid Song Dynasty became troubled by deforestation (due to the demands of charcoal for the iron industry) and desired making ink from a source other than pine soot. He believed that petroleum (which the Chinese called 'rock oil') was produced inexhaustibly within the earth and so decided to make an ink from the soot of burning petroleum, which the later pharmacologist Li Shizhen (1518–1593) wrote was as lustrous as lacquer and was superior to pine soot ink.
India ink has been in use in India since at least the 4th century BC, where it was called masi, an admixture of several substances. Indian documents written in Kharosthi with this ink have been unearthed in as far as Xinjiang, China. The practice of writing with ink and a sharp-pointed needle was common practice since antiquity in South India. Several ancient Buddhist and Jain scripts in India were also compiled in ink. In India, the carbon black from which India ink is formulated was obtained indigenously by burning bones, tar, pitch and other substances.
Uses other than writing
- Hanetsuki (羽根突き, 羽子突き) is a Japanese traditional game, similar to badminton, played by girls at the New Year with a rectangular wooden paddle called a hagoita and a brightly colored shuttlecock. The shuttlecock must be kept in the air as long as possible. Girls who fail to hit the shuttlecock get marked on the face with India ink.
- Amateur tattoo artists will sometimes use India ink for tattooing the skin. Non-medical grade India ink should not be used for homemade tattoos because it contains chemicals which could cause poisoning.
- In pathology laboratories, India ink is applied to surgically removed tissue specimens to maintain orientation and indicate tumor resection margins. The painted tissue is sprayed with acetic acid, which acts as a mordant, "fixing" the ink so it doesn't track. This ink is used because it survives tissue processing, during which tissue samples are bathed in alcohol and xylene and then embedded in paraffin wax. When viewed under the microscope, the ink at the tissue edge informs the pathologist of the surgical resection margin or other point of interest.
- Microbiologists use India ink to stain a slide containing micro-organisms. The background is stained while the organisms remain clear. This is called a negative stain. India ink, along with other stains, can be used to determine if a cell has a gelatinous capsule. A common application of this procedure in the clinical microbiology laboratory is to confirm the morphology of the encapsulated yeast Cryptococcus spp. which cause cryptococcal meningitis.
- Model railroaders use a mixture of India ink and isopropyl alcohol as a wood stain, graying wood to appear aged and to bring out detail.
- India ink is used diluted as an ultra-fine polishing medium for making precise optical surfaces on metals.
- In ophthalmology, it was and still is used to some extent in corneal tattooing.
- Once dry, its conductive properties make it useful for electrical connections to difficult substrates, such as glass. Although relatively low in conductivity, surfaces can be made suitable for electroplating, low-frequency shielding, or for creating large conductive geometries for high voltage apparatuses. A piece of paper impregnated with India ink serves as a grid leak resistor in some tube radio circuits.
- Zoological museum specimens were often tagged in India ink, either directly or on a piece of tracing paper stored along the specimen, because of its durability even when submerged in preservative fluids.
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