Indian ink 
(North American also India ink)
noun [mass noun]
Deep black ink containing dispersed carbon particles, used especially in drawing and technical graphics.When the blood was examined under the microscope a few minutes after the intravenous injection of India ink, distinct black particles of carbon were seen floating among the blood corpuscles....
- The reliability of carbon particles from India ink as markers of cell expansion was an early concern in this study.
- The student applies black India ink with a small paintbrush to the 1/8-inch line or narrow space between the blocks of oil pastel.
Origin
Mid 17th century: originally applied to Chinese and Japanese pigments prepared in solid blocks and imported to Europe via India.
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