To celebrate their 100th anniversary The Royal Meteorological Institute of Belgium (IRM) joined with Belgian Post to produce the first Belgian stamp sheet with heat reactive stamps, where special thermochromic ink responds to changes in temperature. The sheet consists of five stamps: one showing the Institute building and four featuring a tree whose leaves form the map of Belgium. Touching the stamp heats the thermochromic ink and the green leaves disappear, leaving the tree in one of the four seasons!
Issue: 100 Years of The Royal Meteorological Institute of Belgium
Technique: Offset lithography with thermochromic ink
Sheet size: 180 x 140mm
Stamp size: 40 x 30mm
Issue date: 24 June 2013