Gummed watercolour paper tape, or butcher's tape, is a product used to stretch watercolour paper. The technique provides a perfectly flat surface on which to paint. However, using gummed paper tape can lead to problems with removal of the tape after stretching. It's best to leave a margin between your painting and the paper tape, but if that isn't possible, or you are trying to remove tape from an older painting, there are a couple of different techniques you can try.
Moisten the sponge. Do not over-soak the sponge: You do not want to soak the paper, especially if it has already been painted on.
Dab the sponge onto the tape to moisten it. Use as little water as possible.
Carefully peel off the gummed paper tape. If the paper tape doesn't want to peel off, use a light scraping action with the craft knife to release the tape.
Over-saturation of tape adhesive or rushing drying with a hair dryer when stretching watercolour paper can lead to problems with tape removal. Taking your time when stretching the paper will lead to an easier time with tape removal. Use a larger sheet of watercolour paper than you need when stretching with gummed tape, so that you can cut the tape off the edges instead of trying to remove it.
Dampening the paper may ruin watercolour paintings. Instead of trying to remove gummed tape, consider mounting the paper to hide the tape instead.