|MadSci Network: Chemistry|
Permanent inks, like the classic Sharpie, contain three main ingredients: colorant, carrier (solvent) and resin (polymer). For permanence, the colorant of choice is pigments (as opposed to dyes). Pigments do not fade like dyes and do not bleed through paper. Solvents for the old markers (up until the 1990's) were nasty-smelling organic chemicals such as xylene. Nowadays, the solvent of choice is an alcohol (ethanol or isopropanol), which is more enviromentally friendly and better smelling, while still evaporating quickly to prevent messy smearing, etc. Finally, there is a resin or polymer that is added as a "binder" that promotes adhesion... A permanent resin is not permanent unless it sticks like glue to most of the surfaces it is written on. The resin forms a film (once the alcohol evaporates) that allows the ink to write smoothly and uniformly on any surface (smooth or rough) while acting like glue for the pigment. Resins come in all shapes and sizes, typically, urethane acrylic resins are used (like those used in house paints).
I Hope this is helpful.
Keith Allison ("Dr. Crayola")
Binney & Smith, Inc.
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