This question is regarding a matte red/orange coating around the anode socket on a cathode ray tube which is made to be connected to via a cable with a suction cup, the coating seems to typically be a circle just a little bit larger than the suction cup, although in some images I have seen this being a much larger extended area. In my case, I found this on an oscilloscope CRT, although I have also seen this in images online appearing on CRTs from old TV sets. I have found very few mentions of what this actually is online and the information is inconsistent! The consensus seems to be between this having no purpose (which I doubt), and this being insulation which prevents arcing (which makes me wonder why it is necessary in between glass and the suction cup which are already insulators). Would anyone knowledgeable be able to tell me what this substance is and what it does?
The reason I need to know is that I accidentally removed a good part of this coating on an oscilloscope CRT while discharging the anode and cleaning the area under the cup, and need to figure out whether I need to do something to replace it. I have heard about silicone paste being used in this area to prevent arcing, however if the original coating was there for the same purpose, I wanted to find out whether whatever this substance is works better.