Submitted by Member: Nuvistor
When the direct view Mullard Panorama CRT’s were introduced around 1965 they quickly attracted dirt to the screen. The owners cleaned the screens but like windows didn’t get into the corners.
More than one occasion I had to go on a call to confirm to the embarrassed owner it just needed cleaning and not faulty under guarantee.
The first CRT’s of this type had to have a mask to cover the metal band, the mask got very dirty as well and of course we had lots of open coal fires in living rooms which didn’t help.
I think the first Panorama CRT’s I saw were in the Bush TV135U television, A47-18W.
Example in this thread https://www.radios-tv.co.uk/community/black-white-tvs/bush-tv135lu/paged/4/