Comment by Pkeod | Hacker News Reader

Comment by Pkeod | Hacker News Reader

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Different Coloring Agents - Paints and inks have different coloring agents. Paints are made up of tiny bits of colored minerals like clays or talc suspended in a colorless matrix such as polyester or vinyl. A chemical union of tannic acid and iron sulfate dissolved in water or alcohol forms the coloring agent of some inks. Others use such dyes as aniline.

Different Coloring Procedures - Ink soaks into the surface that it colors, but paints do not soak in -- they cover the surface with a coating. In fact, a primer is usually applied to the surface before painting so that the paint won't soak in. For this reason, paint sometimes chips off the surface that it covers, but this never happens in the case of ink.

Surface Protection - Paint not only colors a surface, but also provides the surface with a protective covering that will keep it from deteriorating when assailed by such agents as wind and rain. Ink offers no such protection.

http://www.ehow.com/facts_7225030_difference-between-ink-pai...

Ain't necessarily so (other than the protection thing). While you've described iron gall ink nicely, india ink (lampblack suspended in dilute shellac) would be a paint under your definition, as would many printers' inks (pigments ground into an oil or polymer binder), especially those used for serigraphy. Soaking in isn't necessarily a characteristic of inks either; they are often brittle films (which is why palimpsests exist—old ink was merely scraped off of the parchment/vellum and the ground reused). By the same token, watercolours (which are pretty much universally regarded as paints) do soak into unsized papers.

This is another one of those "where do you draw the line" questions where the line is rather broad and ill-defined. It's a continuum. When it comes right down to it, the intended purpose and traditional usage in the field determine what is an ink, what is a paint and what is a stain.

BTW, note that india-ink doesn't necessarily use shellac, although some modern brands do. Traditional india-ink just uses water (which makes it less permanent than shellac-using india-inks, of course, but it has the advantage of being much easier to clean up).

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