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In another question it was noted that acetone is a useful solvent for removing pencil marks from wood surfaces.

(Source: https://woodworking.stackexchange.com/a/1870/763)

I'm used to acetone being used as a solvent for things like spray foam, nail polish, etc. but was surprised it could 'dissolve' pencil lead. I take it pencil lead is a mixture of graphite & clay substances. What enables the acetone to remove pencil marks?

Perhaps another way to think about this is, why does pencil lead adhere to surfaces like wood or paper in the first place? This is discussed in How are pencil marks "adhered" to the paper? but without mention of using solvents to remove it. How does the acetone reverse or interfere with the adhesion?

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Pencil lead writes on rough surfaces by abrading into tiny particles and getting pushed into surface irregularities. If the surface isn't rough, you would get no visible residue of graphite. A pencil might sometimes even leave a scratch on dense wood that is so smooth that it has almost no blackness from graphite.

Wood is hydrophilic and even contains some water (unless bone dry). Graphite is not so hydrophilic or polar. Acetone wets the wood surface and either swells it by diffusing into watery regions or simply gets between a graphite particle and the wood surface, loosening any van Der Waals forces holding the graphite to the wood. While the surface is wet, the graphite can be wiped off (or smeared out so much that the original mark is not visible any more). Then the acetone evaporates quickly and the wood looks clean(er). Ethanol or isopropanol might do as well - even water (especially with a surfactant to coat and disperse the graphite) might work.

A grease pencil would be much more difficult to remove because so much material is pushed into crevices that a solvent can't easily loosen it without spreading it.

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  • $\begingroup$ I'm vaguely recalling that acetone dissolves some of the chemicals in wood. $\endgroup$ – Hot Licks Dec 22 '19 at 3:06

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