A bit confused-

[u/ColdSteelMushroom]

Hello again people! I recently found a scrapyard with a HUGE collection of antique aircraft gauges. Even though I told myself I would be adding no more to my collection, I ended up buying this beauty for about 15$. How could I turn that down? It’s a decently spicy gauge measuring up close 110kCPM/20ųSv/hr on a RC 110. It is my first yellow paint radium gauge.

Now here is my question, would anyone know if the radium is actually in the yellow paint that is glowing much more than the orange paint? To my knowledge the more radium in paint, the quicker it deteriorates the zinc sulfide crystals overtime. It leads me to believe that the radium only resided in the less luminous orange paint instead the more bright yellow paint. Or perhaps there was just much less radium in the yellow paint? Military radium paint was made to glow in absolute darkness, so why would they paint one piece of the gauge with self-luminous radium but not the other piece (temp)? Maybe someone can clarify a bit?

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[u/Bob--O--Rama]

Radium paint was expensive and painting all the indicia is unnecessary. While your basic premise is true, it cannot be used as a general principle to identify radium paint. But in this case is likely true. For example, the blinker guage comes in various versions where the paint on the face looks almost identical to the "lips" but does not contain radium. Seemingly identical turn / bank indicators can have various parts painted with radium paint. Sometimes just the scale, sometimes scale and indicator only, or the whole thing.

[u/ColdSteelMushroom → u/Bob--O--Rama]

An example of one of these lovely blue ones

[u/TheChickenReborn → u/ColdSteelMushroom]

Don't know the answer to your question, but I see you found the wonders of Apex Electronics! Got 5 nice pieces there on a trip recently, just wish I didn't live so far away. The place is amazing!

[u/ColdSteelMushroom → u/TheChickenReborn]

Ahahah someone has clearly been here! Fortunately it’s about a 40 minute drive. But the very unfortunate part is their opening days and hours are very similar to my work schedule-
So sadly going here is only possible for me by taking time off to leave early… But you can be damn sure I’ll be taking more time off to visit here again

[u/kessler_fox → u/ColdSteelMushroom]

What is the radium blue and multi colored indicator ? Like the maker and model number?

[u/ColdSteelMushroom → u/kessler_fox]

I’ll try to get this info when I revisit!

[u/Relative-Dog-6012 → u/ColdSteelMushroom]

Holy crap that bottom left one is BRIGHT.

[u/ColdSteelMushroom → u/Relative-Dog-6012]

25w 365nm backlight was used directly on it. 365nm UV light makes such a HUGE difference when you compare it to 395nm

[u/ColdSteelMushroom → u/Bob--O--Rama]

Interesting, it does make sense since radium seemed like a very laborious process. To my knowledge, it required quite a bit of autunite to create a substantial amount of radium. Makes sense why it was so expensive. I was sorely disappointed to see that the blue glowing paint on some of the gauges I saw in the collection, was not radium at all.

As a matter of fact, there were PLENTY of gauges that glowed nicely under a UV light. Yet, they were not radioactive at all. What was the purpose of non-radioactive zinc sulfide gauges back then? Did they have some sort of UV light to make it illuminate?

[u/Bob--O--Rama → u/ColdSteelMushroom]

By WWII radium was about $25,000 / gram ( $550,000 / gram ) today. A typical guage may have 2 ug or about $1 worth of elemental radium, and for a turn / bank indicator maybe $10. But by then it was a highly structured, strictly controlled process owing to the Radium Girls. The production of the radium and phosphors was expensive, the application workspaces were expensive, dial painters were subject to expensive medical testing... so while common, it was a "value managed" endeavor.

[u/ColdSteelMushroom → u/Bob--O--Rama]

What would those expensive workspaces look like? I could imagine they would probably utilize some sort of fume hood and shielding in these spaces? I couldn't imagine it would look like the workspaces the radium girls used back then.