The proofs shown here for two different space shuttle stamps capture the change from perforation to die cuts. The 1995 stamps use traditional perforation. But those issued in 1998 are self-adhesives, with die cuts between the stamps.
Both stamps feature photos of the shuttle Endeavour, which is shown lifting off on the 1995 stamp. The 1998 stamp shows it piggy-backed on a modified Boeing 747 for transport.
The typical metal die-cut plate also shown here illustrates how the die-cut process works. The plate was used to slice between self-adhesive stamps, replacing the perforations suited to dry adhesives. Sharp raised rows on the plate form the desired cut pattern. In the die-cut process, an uncut stamp sheet is pressed against the plate. The machine rapidly vibrates the plate against the paper so that the sharp edges cut through cleanly.