The use of fixatives on pastel paintings is a much-debated point among
pastelists. Some artists feel that fixatives darken and dull the colors
in the painting and therefore will not use them. Others feel that
fixatives used properly avoid that pitfall and further, can be used
effectively as a tool to create an impasto effect or to create scumbling
There are two different types of fixative: workable fixative and final fixative. For both, it is important to do light layers, first in one direction and then in another, letting the layers dry between applications.
Workable fixatives (such as Krylon) are mainly used on a work in progress. If the 'tooth' of the paper is fillig up with pastel, workable fixative will allow the build-up of more layers. Fixative can be sprayed in just a small area or over the whole painting Always spray fixative outdoors because of the toxic odor and be careful that you do not splatter or cause dripping (unless, of course, you are going for that effect).
Prismacolor Tuffilm (recommended by the National Gallery of Art in Washington, DC) and Lascaux are final fixatives, used on a finished painting to hold the pastel pigment in place. Used properly they will not darken the colors. Remember, however, that no amount of fixative can completely protect pastel paintings until they are framed under glass.