I'm sure most people here have seen certain old Tube Radios/Equipment with the old totally Gold Spray-Painted-glass valves, like......
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Did that mean that they were special?? (Nope). In fact quite the opposite! Let's digress a bit first......

Later, in valve/tube production, they learnt that "Thoriated Tungten" filiments/cathodes, as well as other Processes, which GREATLY improved the Electron Flow, with lower temperatures. At the same time, Magnesium was used as 'Getters' in the final process. This, when activated, left the typical Silver looking coating on the inside of the tubes. That's a given.

However, there were older and less efficient methods of old. One of them was the "Azide Process", using a totally different chemical process that quickly fell into dis-use. A typical result from those older processes was that the glass insides looked blackened! That in itself was not an issue, except that it was indicative of the old & discontinued process being used, (as well as being a less efficient method!).
For 'Azide' description, see...... http://www.r-type.org/addtext/add011.htm

At one stage, Mullard, (under various manufacturing Names over time), and due to forced cost-cutting needs, at one stage could not afford to upgrade their production system to later/better processes, and were embarrassed to let customers see the typical internal 'blackness'. So as not to draw attention to that fact, they spray painted the whole outer glass in Gold, just to hide what was underlying!!

Their deception later got worse though!! They learnt/utilized what they called a 'Pre-Getter' of Magnesium, just to make the inside glass look 'silvery', (without the gold paint on the outside), before continuing with their (now hidden) old internal process! This was all just a deliberate deception. P.S. I should add, that this has nothing to do with the (usually) smaller valves, that had Gold 'writing' on them, instead of black! Some believe they were of a higher standard etc, however, it was just a result of certain production Anniversaries !!

Not to mention that most of the gold paint was metallic and used as a shield to stop the RF valves from oscillating.
Of cause gold looks classier lol.

The red stuff on the Philips / Mullard tubes was called "Metallisation" & was quite effective while it was on there. Unfortunately people liked to pull tubes out by the envelope which would break the bond (wire) between the envelope and the grounding pin (normally but not always pin one). It also had a habit of coming off, or being damaged.

I did write up an article on how to repair /replace that Metallisation and it did appear in HRSA "Radio Waves".

Thanks for the comments above, by Tallar Carl and Marcc !!
Just as a side note, (regarding Quality), to me one of the issues is 'Robustness'. And I've 'generally' found that a lot of the old Russian made valves to be quite robust & solid in their construction. And I still find that a Plus with a lot of them!!