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This is fascinating. I've walked over those countless times and always wondered what they were. I am curious about this one bit though: > When vault lights wer

This is fascinating. I've walked over those countless times and always wondered what they were. I am curious about this one bit though: > When vault lights were first installed, much of the glass was clear. But when the manganese is exposed to UV rays for long periods of time, it photo-oxidizes and turns purple or pinkish. Hence, the reason so much of the glass is now purple. > This process can take decades. So when you see colored glass, it’s either really old or someone dyed it to mimic the old glass. So what happens to dyed glass after decades? Does it have a deeper purple? Is it made out of materials that _won't_ change color? Something else?

EB66 7y ago
IIRC maganese was used by virtually all American glass manufacturers from the 1800s til 1920ish. So I suppose if the glass was dyed purple, it would turn more purple as it was exposed to UV but only if the glass was manufacturered during that time period.
jdnenej 7y ago
I had no idea these were an actual thing. I just figured it was some whacky street decoration. The ones in Adelaide, Australia are mostly cracked and ruined and seem to be filled in with concrete when they break. I wonder if everyone decided it's easier to use electricity for lighting now.
- eskaytwo 7y ago
  Where are they in Adelaide?
Piskvorrr 7y ago
Perhaps any of these, depending on the materials. Color stability in the long run is rarely a concern.
- jacquesm 7y ago
  That depends on the application. In stained glass and other glass used for art color stability is very important in the long run.
dexwiz 7y ago
Depends on what it was doped (not dyed) with. Dopants like magnesium will slowly move through the glass over time and with exposure to might or heat. These new formations may or may not be optically active in our visible range. Some may be more or less intense or change color over time. Many metals may have many colors based on their state in glass, such as gold.

EB66 7y ago

IIRC maganese was used by virtually all American glass manufacturers from the 1800s til 1920ish. So I suppose if the glass was dyed purple, it would turn more purple as it was exposed to UV but only if the glass was manufacturered during that time period.

jdnenej 7y ago

I had no idea these were an actual thing. I just figured it was some whacky street decoration. The ones in Adelaide, Australia are mostly cracked and ruined and seem to be filled in with concrete when they break. I wonder if everyone decided it's easier to use electricity for lighting now.

eskaytwo 7y ago
Where are they in Adelaide?

Piskvorrr 7y ago

Perhaps any of these, depending on the materials. Color stability in the long run is rarely a concern.

jacquesm 7y ago
That depends on the application. In stained glass and other glass used for art color stability is very important in the long run.

dexwiz 7y ago

Depends on what it was doped (not dyed) with. Dopants like magnesium will slowly move through the glass over time and with exposure to might or heat. These new formations may or may not be optically active in our visible range. Some may be more or less intense or change color over time. Many metals may have many colors based on their state in glass, such as gold.