Pigments can be considered the groundwork of painting. Understanding some details about pigments in wax will help you develop a finished work.
Encaustic has a similarity with watercolor in that it's pigments can separate from the medium if not regularly mixed or stirred. The shear weight of some of these pigments can determine how fast this separation occurs. Many pigments used in encaustic are the same as ones used in any other painting medium; with a few exceptions. Prussian blue for instance, emits hydrogen cyanide gas when heated to high temperatures; concern should also be noted when adding pigment or paint stick.
Pigment separation is not a huge concern for an artist actively painting; the pigment will mix as each color is used. This information is important because pigment concentration does change the transparency and luminosity effects of a painting; a color left unattended could change the intent and look of your work.
A couple of notes to remember: Filling your brush from the top or bottom of a full palette cup when the paint is not regularly mixed can change the pigment concentration held in the brush. The hotter your palette, the faster the separation- the more molten the wax is, means the more liquid the wax is- also keep in mind the proper working temperatures. Read How to Make Encaustic Medium and Paint and Temperatures (Melting and Flash Point) for more info. Returning to a palette or color that has not been used frequently, but has been in a molten state, the color is more likely to be separated and should be stirred.
Pigments during separation can also burn and/or cake up; this leaves a glob of goop in your palette cup. It has been said that zinc white and cerulean blue have a higher tendency for this. Lowering the temperature to the proper setting will reduce separation. Also remove the palette cups that are not being used to help eliminate any problems.
Pigment in encaustic can also be subjective; technically pigments are finely ground rocks, minerals, etc. However, one might argue anything that offers color that can be suspended in the medium can be labeled a pigment (e.g. cake sprinkles, coffee grounds, flax seeds). An artist has to consider much when choosing a pigment, even one loosely defined. Pigments should be lightfast if the color is going to withstand the test of time- so cake sprinkles probably will not be in the mix.
For more information on what to buy read my Art Materials Post: Sennelier Pigments "Encaustic Compatible" and More on Pigments "Encaustic Compatible".
