In addition to the abow described masking methods there is a special designed gluepaint for airbrush masking. This is attached using a regular paint brush, and removed by rubbing.
It can be used instead of the frisket but is some more nasty to the surface, this could result in loss of color. On the other hand it is easier to mask significantly small areas.
It is usually best to combine the different tecniques in the production of a picture.