Novadep has recently built up a new concept of high pressure gas autoclaves with large glass windows thanks to new special tempered glasses. This kind of set-up offers the unique opportunity of in-situ observing the process during the pressure charging, high pressure maintenance and gas release steps. Our design allows for inner pressures as high as 250 bar having a wide field of view of 60mm (reduced field of view allows for much higher pressures). The system called “open-vessel” can be combined with a camera. It also offers the possibility of visualizing processes at temperatures up to 250ºC.