What kind of tape can I use to attach my art behind a mat without it leaving a gummy residue?
Any type of pressure-sensitive tape (one that is tacky to the touch) can leave a residue or be difficult to remove without damaging the art, so when an item is secured to a mat, the safest solution is to either use a reversible, water-soluble starch adhesive and Japanese paper to create the "hinge", or to avoid the use of adhesive altogether and use an edge-support method of securing the art. The most common (and easy to use) version would be a corner pocket, such as archival photo corners. As long as the mat overlaps the artwork enough to conceal the pocket, and the artwork is thick enough to stand being supported by its corners, corner pockets provide a simple and completely reversible way to mount paper artwork.
