Crayola Washable Paint and Markers are water-based and will run or wash off when exposed to moisture. These products work best on porous surfaces. Since pumpkins are nonporous, you may wish to consider another art medium. Crayola Acrylic Paint will provide permanency, however, adhesion may still be a problem. It is always best to test an area first to determine if your paint or marker will adhere to the intended surface.