What happens to paint when it dries?
(Lansing State Journal, July 31, 1996)

Two things happen when paint dries.

First, some of the liquid evaporates.  Paint is made up of two parts, liquid and solid.  The part of the paint that evaporates is what you smell when you walk into a freshly painted room.

To understand how paint dries, you have to know a little about the difference between liquids and solids.

In liquids, the molecules are weakly attracted to each other.  The reason liquids flow is the molecules can slip and slide past each other.

The molecules in solids are strongly attracted to each other, so the molecules cannot slip and slide.  As the paint dries, the attractive forces of the remaining molecules increase to form a solid.

However, in modern paint there is an additional process.  As the paint dries, the molecules become so close that the molecules join to form a molecule that is twice the size of the original.  The combining of molecules continues until all are connected to form one huge molecule.

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