
What are those grids of glass in the sidewalk and why are they purple? - vo2maxer
https://www.kqed.org/news/11791667/what-are-those-grids-of-glass-in-the-sidewalk-and-why-are-they-purple
======
lqet
> Vault lights were used to light some of New York City's first subway
> stations and were placed in the ground of the opulent passenger concourse in
> the city's original Pennsylvania Station.

I will never get my head around the fact that the old Pennsylvania Station was
destroyed. It must be one of the biggest mistakes in urban development of the
20th century.

> Another architectural critic, Ada Louise Huxtable, wrote in The New York
> Times in 1963: "The tragedy is that our own times not only could not produce
> such a building, but cannot even maintain it." [0]

[https://upload.wikimedia.org/wikipedia/commons/6/60/Penn_Sta...](https://upload.wikimedia.org/wikipedia/commons/6/60/Penn_Station_interior.jpg)

[https://upload.wikimedia.org/wikipedia/commons/3/39/NYP_LOC5...](https://upload.wikimedia.org/wikipedia/commons/3/39/NYP_LOC5.jpg)

[https://upload.wikimedia.org/wikipedia/commons/thumb/d/d9/So...](https://upload.wikimedia.org/wikipedia/commons/thumb/d/d9/South_facade_from_southeast_-
_pennsylvania_station.tif/lossy-page1-1280px-South_facade_from_southeast_-
_pennsylvania_station.tif.jpg)

[https://upload.wikimedia.org/wikipedia/commons/f/f8/The_New_...](https://upload.wikimedia.org/wikipedia/commons/f/f8/The_New_York_improvement_and_tunnel_extension_of_the_Pennsylvania_railroad._Issued_October%2C_1910_%281910%29_%2814573203608%29.jpg)

[https://live.staticflickr.com/5085/5383028384_a22f3605e4_b.j...](https://live.staticflickr.com/5085/5383028384_a22f3605e4_b.jpg)

[https://static01.nyt.com/images/2019/04/24/lens/24pennnstati...](https://static01.nyt.com/images/2019/04/24/lens/24pennnstation-
ast-5/merlin_148714782_bb4b9b98-bded-4d9d-b4e6-f2a13d819201-superJumbo.jpg)

[0]
[https://en.wikipedia.org/wiki/Pennsylvania_Station_(1910%E2%...](https://en.wikipedia.org/wiki/Pennsylvania_Station_\(1910%E2%80%931963\)#Demolition)

~~~
chrisseaton
> the old Pennsylvania Station

It wasn't that old! It was only built in 1910, and using modern techniques! It
wasn't an ancient monument as you probably think it was, and it was only
around for a few decades.

Equivalent of a 1960s building being knocked down today.

~~~
inferiorhuman
_Equivalent of a 1960s building being knocked down today._

There are plenty of buildings from the 60s I'd be sorry to see go. At the top
of the list is the Marin County Civic Center and the TWA Flight Center.

~~~
Benjammer
JetBlue turned the TWA center into a hotel, I don't think they plan on getting
rid of it any time soon.

~~~
kaishiro
And a rad one at that - stayed there on the way through JFK a few weeks ago.
If you’re feeling fancy you can even take a Blade helicopter into the city -
they have a desk right at TWA.

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taeric
I thought this was going to be in Seattle. :) It is neat to notice these all
over the place.

The underground tour is more than a little crazy to see just how built up the
city literally is. My favorite related topic were the spite mounds.

~~~
hinkley
I think the Seattle Tour has a bunch of factoids of which each guide chooses
their own subset. First time I took the tour, they mentioned that a bunch of
the material for raising the streets came from San Franscisco, which had quite
a thirst of lumber (and would occasionally catch fire and burn down, boosting
that demand).

Flat bottom boats hold a lot of bulky cargo, but they're a nightmare when
empty. So on the return trips they ballasted them... with fill dirt.

~~~
vineyardmike
That tour is great! I take everyone who visits seattle to it. I've had the
same tour guide, and each time was different as well.

~~~
nogabebop23
Slightly off-topic; The Seattle free walking tour (pay what you want after) is
also great, epsecially for a first time visitor. My wife and I happily shelled
out after the 2-hour version.

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StClaire
Denver has these, you can see them on Larimer and Market street in LoDo.
Around the 1890s, the locals dug out a series of tunnels through the city. The
snows would come in and people would just go underground for a few days for
business. There was a bar that closed about a year ago called the Blake Street
Vault—it used to be a bank—and if you asked they would take you into the
basement to see the vault and the dumbwaiter. You can see down where they
plastered over some of the wall, it used to have a teller window right there
open to the tunnels for customers.

Supposedly, you could go from Union Station all the way to the capital
building underground (but I doubt that).

I’m sure most of the tunnels aren’t passable, possibly collapsed, filled in,
or flooded. But I seriously want to go down and try to map out some of them to
be restored like they did in Seattle.

~~~
rconti
Stupid question: Wouldn't the snow cover the vault lights? (I know, they could
clear them by clearing the sidewalks...)

~~~
sampo
Snow also scatters light a lot, if it's not too dirty. One example I found, it
takes about 8 cm (3 inches) of snow to reduce the light irradiance to half.

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BinaryIdiot
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?

~~~
jdnenej
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
Where are they in Adelaide?

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glangdale
Thaddeus Hyatt, the inventor of those grids, has a fascinating history,
including backing militant abolitionists (I think it's unknown whether he
bankrolled John Brown) and being jailed by the Senate (?) for refusing to
testify.

~~~
brlewis
Wikipedia states his financial support of John Brown as fact:
[https://en.wikipedia.org/wiki/Thaddeus_Hyatt](https://en.wikipedia.org/wiki/Thaddeus_Hyatt)

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austinjp
The Wikipedia entry on prism lighting is... illuminating:
[https://en.m.wikipedia.org/wiki/Prism_lighting](https://en.m.wikipedia.org/wiki/Prism_lighting)

~~~
djmips
Is this is the same thing but at a larger scale than the light diffusion used
in flat panel displays?

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ChuckMcM
I really love these, there was a story about a modern version here:
[https://www.youtube.com/watch?v=tJD-D2uLX70](https://www.youtube.com/watch?v=tJD-D2uLX70)
where African's use plastic bottles filled with water as vault lights.

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AstroJetson
I had a sail boat where the prior owner had installed 4 of these in the cabin
roof. They were little domes and did a good job of lighting the cabin in the
day, and marking a path at night.

~~~
hinkley
I learned about these many years ago, but the whole "you can see a fire in the
hold" angle never occurred to me. Accurate, useful, and macabre.

~~~
sandworm101
A watchman on deck could also see if a thief is rummaging around down there
while the boat is in port.

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evanthayer
I restored many old cast iron buildings in NYC that used “bullet glass” paving
for the sidewalk above the vault below. These are still manufactured by Circle
Redmont (approved by NYC Landmark Preservation Commission) and are beautiful
but expensive.

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daxorid
This is interesting, but raises a question. The article mentions:

 _In San Francisco, vault lights are mostly used to illuminate sub-sidewalk
basements — ie. basements that extend under the sidewalk._

How does this work, legally? Where I live, sidewalks are property of the city
(or the HOA, in some cases), and I'd presume the same in SF. Does the title of
the sidewalk-adjacent property allow you to excavate N feet beyond the
property line? Or is the sidewalk instead a publicly-managed easement on your
own property? Who pays for installation and maintenance of the vault lights?
How does coordination of engineering/construction of the sidewalk-basement
boundary work?

~~~
yardie
That must be a western concept. On the east coast it's common for sidewalks to
be owned by the landowner yet have to remain unencumbered for the public right
of way. Some owners find out the hard way that they are also responsible for
maintaining the sidewalk when the city hits them with a notice.

~~~
cr0sh
> Some owners find out the hard way that they are also responsible for
> maintaining the sidewalk when the city hits them with a notice.

I live in Phoenix; in my neighborhood it's basically the same way. City comes
around, tears up the sidewalk to fix something (water main or such) - and you
the homeowner are responsible for fixing the sidewalk. Yay.

About all the city will do is put some asphalt over the bare dirt, but if you
want the sidewalk to be concrete, you have to pay for that work.

Since a lot of the properties in my neighborhood are rentals, you can guess
how often such asphalt patches are properly "fixed". Usually, you have to put
in a blight notice to the city to have them contact the actual homeowner to
get them to actually fix it properly.

One of the downsides living where I do. But then again, I live "below my
means" (as an SWE), and I don't have an HOA, and block construction, and I can
work on my cars when I want, where I want, how I want. If that means an angle
grinder and welder come out at 8pm, so be it. Neighbors can't complain until
after 10pm or so, and only then for excessive noise.

Take the good with the bad...

~~~
GhettoMaestro
> I live in Phoenix; in my neighborhood it's basically the same way. City
> comes around, tears up the sidewalk to fix something (water main or such) -
> and you the homeowner are responsible for fixing the sidewalk. Yay.

What in the holy hell? That's insane and ridiculous. Is this for both
residential and commercial? (I could understand the latter slightly more.)

Sounds like a great way to piss off your citizens by cutting a very small
corner in what is probably already an expensive endeavor.

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markstos
"Hyatt’s innovation in subterranean lighting made him rich as his vault covers
were used all over the country. With his newly acquired wealth he spent much
of the rest of his time and money fighting for the abolition of slavery."

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dcminter
Perhaps the inspiration behind this?
[https://www.bbc.com/news/magazine-23536914](https://www.bbc.com/news/magazine-23536914)

~~~
egypturnash
The article makes it sound like he came to it separately from just playing
around with light refraction in water, using an easily-available container.

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huangc10
I walk past these all the time thinking they're just interesting design
patterns on the floor...how dumb of me. Insightful article and fun read.

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aclatuts
I always thought it would be interesting to build vertical greenhouses with
something like this, in the floors or walls, siphoning natural light between
the floors

~~~
Scarblac
Modern greenhouses are often fully automated and have no need for floors.

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bynkman
I know of a few places in Kansas City that have under sidewalk vaults. In some
of those places they have warning signs about not parking. Here's one.
[https://bit.ly/36qPLvy](https://bit.ly/36qPLvy)

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ilammy
Modern people accustomed to ubiquitous electrical lighting would probably
think of 19th century and beyond as quite dark.

~~~
sandworm101
It was. Very dark. The changes brought by electric light cannot be overstated.
In my lifetime, LEDs brought portable light in the outdoors from an expensive
and dangerous luxury (candles, lanterns etc) to something innocuous and
expected. Camping and working outdoors today is totally different than even 25
years ago.

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Angostura
Lots in London, and many very old - but I've never spotted purple ones.

~~~
lgeorget
Well, the color being due to exposition of the prisms to UV radiation, it will
take a lot longer to reach the purple tint in London than in California.

~~~
Symbiote
It's more likely that British glass manufacturers used a different chemical.

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altgeek
In downtown NYC, there still are areas of sidewalk with these.

~~~
abuckenheimer
Just remembered the puck building[1] has these on the sidewalks surrounding
the Houston street side, if you go into the Eastern Mountain Sports store and
down the stairs you can see them from below.

[1]
[https://en.wikipedia.org/wiki/Puck_Building](https://en.wikipedia.org/wiki/Puck_Building)

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RangerScience
Oh neat! I didn't know that Sacremento has this kind of underground.

Also, anyone else having flashbacks to Dinotopia sunstones?

~~~
SubiculumCode
Indeed. I've been living in the area for some time now and had no idea. I
wonder if there is some area that can be explored?

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robk
These are ubiquitous in London

~~~
oneeyedpigeon
Notably the ones in Crystal Palace [1] which are above an old underground
toilet, now converted into someone's house! [2] I guess — in this case, at
least — the fogging-up of the glass is actually a privacy feature.

[1]
[http://1.bp.blogspot.com/-SuRJ4LN5LhQ/T3GQS8rUN9I/AAAAAAAAAM...](http://1.bp.blogspot.com/-SuRJ4LN5LhQ/T3GQS8rUN9I/AAAAAAAAAMo/GkBQCh0GctM/s1600/external+complete.jpg)

[2]
[http://crystalpalacetoilets.blogspot.com/](http://crystalpalacetoilets.blogspot.com/)

~~~
jaclaz
Only for the record, there is a "modern" material, called "glass block" since
the '50's or '60's, the one in your photos seem like it (and there is no
"prism" like the kind described in the main article) that can be used also for
walls.

Example:

[https://www.sevesglassblock.com/wp-
content/uploads/2018/03/T...](https://www.sevesglassblock.com/wp-
content/uploads/2018/03/Technical_Guide_en.pdf)

(go to page 54 of the .pdf)

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ndesaulniers
Eureaka in Mountain View, CA, across from Red Rock Coffee Shop, anyone?

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im3w1l
One thing I would have liked the article to explain is when this is preferable
over solid glass.

~~~
WorldMaker
Safety/stability, presumably, given that people might stand on top of them
(many of the examples here are embedded in sidewalks) and they'd need to be
weight bearing. Safety glass is a relatively more recent invention than some
of the examples (at least one example in the article dates back to the mid
19th century), and a very recent invention if specifically restricting to the
types of plastic-based laminated glass trusted in things like modern car
windshields and observation floors today.

~~~
WorldMaker
Also, the article points out that many of them had interesting prismatic
shapes to bounce light around in interesting directions, and making those
prisms would be easier as smaller individual components rather than one large
piece of glassblowing, even if they had the technology to make it safe enough
at that size.

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8bitsrule
Looks as though these might be most common in older port cities. I first saw
them in Duluth (the tip of Lake Superior) but not in other cities in the
region. Possibly the vault-light salesmen travelled by ship a lot!

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jedberg
If you’re ever in Seattle and this kind of thing fascinated you, I highly
recommend the downtown underground tour.

This is one of the things they cover.

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agumonkey
interesting, lest reuse old batteries manganese dioxide and remelt glass
bottles :)

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loeg
You see these around the south end of downtown Seattle too.

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zbentley
They look like "Dinotopia" Sunstones.

~~~
adrianmonk
Or "Land of the Lost" crystals:

[https://landofthelost.fandom.com/wiki/Crystals](https://landofthelost.fandom.com/wiki/Crystals)

especially as seen in matrix tables in the pylons:

[https://landofthelost.fandom.com/wiki/Pylons](https://landofthelost.fandom.com/wiki/Pylons)

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coolblah
Research mudflood to go way down this rabbit hole.

