Photon detectors are indispensable in many areas of fundamental physics research, particularly in the emerging field of particle astrophysics, as well as in medical imaging and nuclear non-proliferation. For a significant progress in all these areas a new, inexpensive industrial mass-production photosensor technology is needed. In order to reach that goal we have introduced several innovations. This paper focuses on one of them, the ReFerence flat-panel photon detector. We report on the prototype development, and in particular on the development of a new oxidation-free method for vacuum sealing of glass panel surfaces with liquid indium, at processing temperatures below 360°C.