Within
candle making there is a question of how to color the candle. There are
dyes and there are
pigments - and each has its own properties and use.
Pigments are particles of color that are suspended in the wax
and thus do not dissolve, migrate or 'bleed' once the wax sets in position. Often, pigments are used in a wax that is used for over-dipping which just colors the outside of a candle. They are also not as susceptible to color fade. The color in crayons is made from pigments.
Dyes, on the other hand, are often in a liquid or a powdered form and
tend to bleed as the essence of the color moves about. Dyes also are more translucent than pigments and give more control over the shade of the color that is the wax takes on.
When burnt, pigments tend to clog the wick (a bad thing). This makes them unsuitable for complete coloring of a candle. For this reason, it is often used in over-dipping which just coats the outside of the candle in color and thus not affecting the wick. Furthermore, if a pigment is used to color the main body of a candle, the wax should be well stirred and avoid pouring the last bit of wax into the mold - some of the particles may have settled to the bottom of poured wax and leave dark specks in the wax.