The standard "Bulletproof" black ink from Noodler's. It is resistant not only to water and light, but also bleach, solvent, alcohol, etc. The color comes from a compound that binds to the cellulose in paper, as opposed to traditional dyes or pigments. Can be harder to clean from pens than traditional water-soluble dyes. Also known to have long dry times that can be reduced by diluting the ink with distilled water.
by Prolix