Inktense are a range of watersoluble pencils made by Derwent that contain ink rather than watercolor. Unlike watercolor pencils, when the ink has dried again it won't lift off easily when you rewet it. To use Inktense pencils for a fabric painting project which you think you might wash at some stage, work with fabric painting medium rather than just water to make the ink permanent.
You'll need some Inktense pencils, a pencil sharpener, a stiff-haired brush, fabric painting medium or fixative, a tube of blue acrylic paint, and some 100 percent cotton fabric or lightweight canvas. A tight-weave fabric is easier to paint on than a rough one. Prewash the fabric you'll be painting on to remove any coating that may be on the fabric. Yes, it's a pain to do, but not as painful as to discover your paint doesn't want to stick to a section of the fabric! Once it's dried, you're ready to start painting... (I don't usually iron the fabric as the creases come out when the fabric gets wet as you paint anyway.)