There are several types of tape that watercolorists use, the one I believe Aggie is referring to is a 'washout tape' it will even preserve deckled edges. The other type of gummed paper tape will result in over 50% fibre tear (read big mess) if you try to remove it... usually cut off with blade and straight edge. If you do not want a hard line containment you could always use an art masking fluid feathered out in addition to the tape, it is quite benign and easily removed.