I think the answer is electron shell.
The melting point is the temperature a substance must reach to go into its liquid phase (or solid) and a boiling point is the temperature a substance must reach to go into its gas phase (or liquid). For example, water must be 0ºC to melt or freeze and 100ºC to boil.
It would have to be paints consists of pigments,solvents, and binders. Once the [paint has been applied and has dried, the pigments are still able to determine the matched samples.