Pastel is pure pigment with an adhesive added to hold it together and chalk to modify the color. For the best effect pastel is applied to a lightly textured or rough surface that provides the tooth to hold the pastel on the surface.
Using pastel on a sanded surface gives a full bodied look that rivals oil painting and is more durable. My most detailed formal portraits are done on a sanded surface.
I always work actual size and from life when making a portrait. The time required to complete a portrait varies with the medium and the amount of detail required. Enjoy!