As asked in the question and also, a bonus question: which property of a chemical would make it 'permanent' in terms of markers?
The "permanence" is just a reference to it being waterproof.
In general, the ink comprises a main carrier solvent, a glyceride, a pyrrolidone, a resin and a colorant.
This is mostly the result of solubility. There are other markers sold on the market with labels such as "buff proof" (slang for removal proof), that are really just pens that use a different carrier solvent. With those, typically organic solvents would be the correct solvent for removal.
1$\begingroup$ This composition is taken from a patent, isn't it? $\endgroup$ Sep 16, 2014 at 9:42
$\begingroup$ The quote is from the Wikipedia. $\endgroup$ Sep 16, 2014 at 14:41
$\begingroup$ I added the second part about the other class of markers from personal experience. $\endgroup$ Sep 16, 2014 at 14:43
Basically, ink is a liquid or paste made up of pigments or dyes that is used to color a surface to create printed words or pictures. Modern inks are often made of complex combinations of various chemicals, including solvents, pigments, dyes, resins and other materials.
The chemicals found in permanent markers--xylene, toluene and urethane resin--are what give these markers their characteristic abilities to handle unusual surfaces and leave long-lasting messages. While substantial or prolonged exposure to these chemicals is harmful and toxic, the amount present in a permanent marker is minimal for the casual user.
This is what I got from google search. The above mentioned chemicals are most oftenly used, which make ink permanent. However If you have notice you would realise that the ink actually is not permanent, it fade away after certain period of time!
6$\begingroup$ This answer is just plain wrong. Permanent markers are permanent because they use ink that is not water-soluble (that's where the xylene and toluene come in) and pigments or dyes that don't fade. Adding xylene, toluene and urethane to a non-permanent ink wouldn't make it permanent. $\endgroup$ Sep 16, 2014 at 8:45
1$\begingroup$ @DavidRicherby I don't get were it is written in the answer that permanent ink is prepared from non-permanent ink. In answer Hey has tried to explain how permanent ink differ from normal ink. $\endgroup$– user7484Sep 16, 2014 at 13:37
$\begingroup$ @RutvikSutaria The answer implies that permanence comes from the inclusion of substances such as xylene, toluene and urethane but just including those substances doesn't make an ink permanent. Apologies for the rather opaque phrasing of my original comment. $\endgroup$ Sep 16, 2014 at 13:39
4$\begingroup$ @DavidRicherby I think you should give answer to this question. $\endgroup$– user7484Sep 16, 2014 at 13:40
$\begingroup$ @DavidRicherby, I have worked with "Permanent" markers in my job for several years. They worked pretty well until the toluene and xylene were removed by the manufacturers. They used to withstand removal from vinyl products when I used plain isopropyl alcohol. Now, they can be easily removed with it, without any effort. Allot of them will state "Xylene Free". We are down to one product, from one manufacturer, that stains in the manner we require. All others we have tested, wipe off with a rag and alcohol. $\endgroup$ Mar 13, 2017 at 18:30
In my experience, ink of a permanent marker can be removed by drawing over it with a non-permanent marker and wiping it off (success depends on surface). The same goes for non-permanent writing that can't be removed because it is too old. Expo (apparently a company that sells markers and related stuff) confirms this in their FAQ
the big question:
how do I get permanent marker off a whiteboard?
No worries if those pesky permanent markers make their way into your whitespace. Just draw over it with an Expo Dry Erase Marker and poof! It's gone.
From this I would conclude that non-permanent markers contain some solvent that permanent markers lack. But obviously, permanent markers need some solvent, too. Otherwise, you wouldn't be able to write in the first place. So it must be some solvent that evaporates quickly while the solvent in whiteboard markers doesn't.
If you search for ingredients of whiteboard markers, the organic solvents Xylene and Toluene keep popping up, so that's obviously not the answer.
Whiteboard cleaners contain all kinds of organic solvents that evaporate much faster:
the main ingredient is isopropyl alcohol, which is sometimes called "rubbing alcohol." Other ingredients may include 2-butoxy ethanol and (di)chloroacetic acid.
ISOPROPANOL (ISOPROPYL ALCOHOL), 2-PROPANOL, DIMETHYL CARBINOL
2-BUTOXYETHANOL (ETHYLENEGLYCOL MONOBUTYL ETHER), BUTYL CELLOSOLVE, BUTYL GLYCOL, GLYCOL ETHER EB
Given the wide range of possibilities, the actual chemicals used probably depend on the marker's brand. Isopropyl alcohol seems to be a good bet, though.
It also evaporates quickly, leaves nearly zero oil traces, compared to ethanol, and is relatively non-toxic, compared to alternative solvents.
To answer your more generic "bonus" question:
which property of a chemical would make it 'permanent' in terms of markers?
- The ink needs to waterproof, i.e. not water soluble
- The solvent needs to vaporize quickly
6$\begingroup$ This appears to be speculation rather than an actual answer. There is no race to answer questions here. If you don't know the answer, at least wait a couple of days to see if somebody posts something authoritative before posting possibly-helpful speculation. $\endgroup$ Sep 16, 2014 at 8:47
1$\begingroup$ Aren't Isopropanol and 2-propanol the same thing? $\endgroup$– user137Sep 16, 2014 at 15:09
$\begingroup$ yes, it's also the same as dimethyl carbinol. The 4 chemicals in the line below are also synonyms for each other. $\endgroup$ Sep 17, 2014 at 7:49
Regarding the bonus question: Permanence will depend on resistance of the resin to water and solvents, which may be obtained using a resin that self-crosslinks at room temperature. Alkyd paints contain this type of resin, but there are many other possibilities. You also need to protect the bond between resin and substrate, which gets tricky, because of so many possibilities for the substrate's chemical structure -- relatively easy to stick to wood or acrylic, but hard for polyolefins, especially if fluorinated. An ideal resin would be of low molecular weight and a good solvating power for the substrate, so it would penetrate somewhat into the surface, and then chemically attach as well as self-crosslinking.