Instructables link: http://www.instructables.com/id/Fading-Domes-Thermochromic-Painting/
documentative video: https://vimeo.com/197175143
The surface of the painting is coated in thermochromic pigment, which is black at ambient temperature and becomes transparent when heated.
Three resistive wires are shaped into an engraved sheet of Perspex, forming the perimeters of three famous Italian domes (San Pietro and Sant’Ivo alla Sapienza in Rome and Santa Maria della Salute in Venice). These are then connected to a battery through three buttons that interrupt the circuit.
Once the buttons are pressed the energy flows and heats the resistive wires, which are placed directly behind the thermochromic ink layer, heating the pigment and thus changing its color.