Pastel are made from dry pigment as are all mediums, what differs is the binder that holds each medium together. For pastels this is gum tragacanth or a chemical compound Methyl Cellulose. Different pigments have varying self binding properties and binders needs to be prepared according to these properties. I leave this to the experts but there is a way to make a personal contribution to your pallet which is both simple and economical.
Working in pastel usually results in the acquisition of a large quanitity of pastels with a varying quality and colour range, many of which may be duplicates or colours that are rarely used for your subject matter. What I have found is that makers who sell sets of pastels tend to select too many high chroma sticks and too few neutural leaning pastels. My aim is to reproduce the colours I use a lot or create colours ranges that are not available.
THE 7 SLIDES ABOVE TAKE YOU THROUGH THIS PROCESS.