Cleaning the glass CRT

[SavannahLion]

When I was prepping monitor number five for testing, I remembered that, before I purchased it, I spotted a very thin spiderweb effect on the outside of the tube when the guy was trying to show me it worked. I simply made the assumption that this was what ammounted to high voltage "static" due to the excessive dust coating the back of the tube and the moisture (the monitor came from a cab stored outside in the rain) that was no doubt present at the time.

So I grabbed an old T-shirt to wipe off the dust when I reflected for a moment. Is there a possibility the flyback cap could have a gap causing a current to leak out causing this spiderweb effect? Naturally, I would need to ground the tube, but I want to avoid getting any crap in the cap hole while cleaning. This lead me to thinking about one thing after another until I remembered an article about CRTs I read recently.

If I do clean it, do I need to be concerned about a "coating" on the outside? I recall reading an article about CRT's that explained that tubes are coated on the inside and outside with a conductive layer effectively turning the entire tube into a high power capacitor. OK, that makes sense. What stuck in my mind from the article about this was how the author made it an explicit point not to clean the back of the tube. OK... why? What is this conductive coating on the outside? Metal or the black dust that coats the back? With this spiderweb crawling around the back of the monitor, I would think removing the dust would be a good idea... to get a better idea of what's going on with the monitor and remove a place for moisture to hide.

Four of the five monitors I'm working have varying levels of filth on the back of the tube. I'm not really interested in getting a nice pristine cabinet constructed/restored only to stick an ongodly disgusting monitor in there.

[SirPeale]

You can easily see the coating on the outside.  It's the black stuff that's not glass. 

It's important stuff.  While you might be able to get away with some *MILD* scratching, you don't want this stuff to come off!  Use a gentle glass cleaner to clean the back of the tube.

[SavannahLion]

You can easily see the coating on the outside.  It's the black stuff that's not glass. 

It's important stuff.  While you might be able to get away with some *MILD* scratching, you don't want this stuff to come off!  Use a gentle glass cleaner to clean the back of the tube.

I better put away my copper bristle brush then.   

From your description, it's not the powdery black soot or dust then but underneath it. I can clean it off. I've seen the dust/soot on so many junk CRT's, I've forgotten it's not supposed to be there. 

I've got enough old cotton T-shirts that should do the trick. You figure Windex is gentle enough or is this coating some kind of metal, ie prone to rust?

[Lutus]

just wipe it off with the dry t-shirt

You will get enough of it off to do the trick.