Scotch (3M) sells three varieties of ready-made double-backed tape for sticking together two flat surfaces. Their Double Stick Tape (model #137) does what a self-connecting loop of ordinary tape does, but more tidily and sure. Their Double-Sided Tape (model #667) is similar but you can re-position the tape. For most uses – scrapbooks, posters, etc – I much prefer this kind. Their Photo Mounting Tape (Cat. 002) is double-side, not positionable, but acid-free. This is what you want to use for archival stuff.