What are those grids of glass in the sidewalk and why are they purple? | Hacker News Reader

What are those grids of glass in the sidewalk and why are they purple?

kqed.org

803 pointsvo2maxer116 comments

> 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/3/39/NYP_LOC5...

https://upload.wikimedia.org/wikipedia/commons/thumb/d/d9/So...

https://upload.wikimedia.org/wikipedia/commons/f/f8/The_New_...

https://live.staticflickr.com/5085/5383028384_a22f3605e4_b.j...

https://static01.nyt.com/images/2019/04/24/lens/24pennnstati...

[0] https://en.wikipedia.org/wiki/Pennsylvania_Station_(1910%E2%...

Interesting enough the glass floor was never removed during the demolition of the original Penn Station and can still be seen from the track level. Of course the floor has been tiled over and no longer functions as a light source, but it serves as a hidden reminder of the old Penn Station.

https://ny.curbed.com/2018/10/23/18009496/penn-station-new-y...

Seems like some New Yorkers ought to petition to un-tile-over the floor and bring back the glass.

> 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.

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.

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

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.

It’s pretty beautiful inside.

"Equivalent of a 1960s building being knocked down today."

I feel like you refuted your first sentence with this!

A 1960s building is old, but 80 years isn't really enough to inspire awe; there are plenty of existing structures several hundred to several thousands of years old.

https://en.m.wikipedia.org/wiki/List_of_oldest_known_survivi...

"A 1960s building is old, but 80 years isn't really enough to inspire awe;"

That's absolutely untrue. Plenty of buildings inspire awe immediately upon completion and plenty of them have gone through their entire life-cycle within a span of 60 years. Try Quarry Hill Flats for a start. https://duckduckgo.com/?q=quarry+hill+%2Bflats&t=opera&ia=im...

"there are plenty of existing structures several hundred to several thousands of years old."

This is a bizarrely obvious statement, like, who doesn't know this?

Also, we're not just talking about a "structure" like the pyramids or various ancient monuments, Penn Station had an _function_ it was needed for.

Not many "several thousand year old" structures with a function exist except as museums now. There's a house somewhere that's been continuously inhabited for about a thousand years (Faroes maybe?) and a few of the forts or religious buildings still in use are older, but most structures this old are, like the pyramids, just a tourist attraction now. New York did not need another museum, it needed a railway station.

A friend of mine’s dorm room at college was a thousand years old.

Speaking of bizarrely obvious statements...

> Plenty of buildings inspire awe immediately upon completion

I'm speaking specifically about the age. Some things are special for [what they are], and some things are special for [what they are given their age]. A 1963 Mustang is 'a classic'; 1993 Mustang is just an old car (even though the '94 mustang was built with 30 additional years of auto innovation, people are much more awestruck when they come across the 64').

So to summarize, Penn Station was architecturally marvelous in 1910 when it was completed, but by 1963 it's likely people just thought of it as an old run-down train station. Like a just-old car. Of course now we are like - with a bit of restoration that shit would be a classic.

"I'm speaking specifically about the age."

Yes. You specifically said that a 60 year old building is not old enough to inspire awe. And I rightfully replied that that is nonsense. My statement was obviously not obvious to you.

Nope. I said "80 years isn't enough to inspire awe". Do you honestly think someone wouldn't consider any building whatsoever to be awe inspiring unless it is over 80 years old?

Let me put it this way - is there any car from 1995 that is awe inspiring? Maybe yes, perhaps some lambos or rolls royce models. But those were killer cars in 1995. Even better brand new. 25 years isnt enough to make them more cherished than when they were new though. They go down in value through those 25 years. But 50 years... they start to surge back up in price. Why? Because the age factor starts to inspire awe - cars if that age driving around are rare sights. With buildings, 80 years or less doesnt quite do it, particularly when there are lots of buildings that are hundreds of years old.

If Penn Station was 300 years old, and someone proposed tearing it down, people would laugh. But in 1960, at 80 years old, Penn was just an old train station in disrepair.

Age isn't what inspires the awe, though.

Then why are we talking about the age?

Lost craftsmanship and cost of construction has risen so much that some projects just couldn't be afforded anymore. My city once had an extensive rail network, it was torn out in favour of cars. Now that we want to put it back in, construction costs are so inflated we can't afford it.

If it's in America, it isn't a matter of not being able to afford it; we choose not to, instead prefering to waste it on military spending. Our country really could be great again if we chose to stop that madness.

You're about to engage in several major public works worth of military spending.

Just to emphasize, that's not like a train station worth. It's like a complete bullet train system between all major USA cities would cost less then the iraq war. That's the scale of the invisible, opportunity cost "infrastructure damage" cause by these wars.

I'm totally fine with using public funding for projects that have lasting social good.

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.

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.

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.

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.

When I first learned about raising the streets at massive scale in American cities (Chicago Seattle etc.), I was very fascinated. I’m not sure if this is/was an unique American exercise.

Medieval cities used to do this; essentialy a transition from a small town to an actual city, i.e. "we are no longer able to fit the place to nature, let's do the opposite thing then."

See also Rome, which is built on top of about eight more layers of Rome. Residents often get architectural and history students asking to look at something weird in the basement.

The new Seattle waterfront sidewalks have a similar inlayed motif of large purple glass tiles. Was cool to notice the design inspiration.

https://www.washington.edu/news/2017/05/18/seattle-seawalls-...

https://www.kuow.org/stories/seattle-s-new-seawall-was-built...

I grew up in Seattle. I still need to do the tour some day when I visit. So many cities have underground tours and I've heard great things about them.

I did it last time I was out there..., I had fun and some time to kill before my flight.

The tour guide makes the tour interesting. The actual sights are cool but you're effectively on a guided tour through maybe a few small blocks of buried sidewalk. It is not earth shattering stuff though the history is definitely cool.

In the end it was worth the ~$40, $20 for the tour I think, and I felt generous so I gave the guide a big tip since he was hilarious and took us on a slightly extended route according to some folks who had done the tour in the past.

https://mashable.com/2015/08/18/building-seattle/

If you've already done the normal underground tour, there's also a late-night version where they talk about the seedy underbelly of early Seattle, i.e. all the prostitution and body-snatching and other assorted crimes. Or at least there used to be one.

They mentioned a bit of that on our tour. With kids ranging from 5 to 10, it was kind of funny to see the looks. (My kids, to be clear.)

I got the impression it wasn't much of an under belly, as it was a large part of the life around here.

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.

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

It would. But not 100%. Same with skylights, depending on the depth and density some sunlight still makes it

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.

They weren't clearing the sidewalks to let light through, they were (and we are) clearing the sidewalks so that people could walk on them! Anyway, with or without prism tiles.

I've got some friends in Minneapolis that November - ~May don't leave the skyway system. Seems similar, but connects buildings at the 2nd story instead of underground.

http://www.skywaymyway.com/

We have these old glass grids in the sidewalks along College Ave up here in Fort Collins as well. Some are even still in use by restaurants to load inventory from the Cysco / Shamrock trucks.

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?

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.

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.

Where are they in Adelaide?

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

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

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.

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.

Wikipedia states his financial support of John Brown as fact: https://en.wikipedia.org/wiki/Thaddeus_Hyatt

The Wikipedia entry on prism lighting is... illuminating: https://en.m.wikipedia.org/wiki/Prism_lighting

This article is fantastic and answers a lot of questions I didn't know I had!

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

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

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.

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.

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

Yes had one in my old boat. Nice, but not so nice where I'd install them on my current sailboat.

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.

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?

I would guess these situations pre-date any of the current zoning laws.

This is correct.

It depends on how the lines are drawn. If you want to plow a road through existing houses today, it gets condemned -- taken by the government, lock, stock and barrel. In a new subdivision, they'll often deed the streets over to the city.

But sometimes, especially in the old days, the city just got a "right of way," not title to the land. And in that case, the owner could do anything it wanted, so long as it preserves the right of way. So if the city had a right of way to a sidewalk, it doesn't matter what you do under the sidewalk. Here's an interesting discussion about right of way edges that appears to use Washington (State) law.[0]

[0] http://mrsc.org/Home/Stay-Informed/MRSC-Insight/November-201...

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.

e.g. keeping them cleared of snow. So if you are traveling and there's a snowstorm you're basically responsible for finding someone who will clear it for you.

Same thing in SF. Owners are responsible for maintaining the sidewalk, and the city will let you know when you need to repair them.

> 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...

> 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.

As far as I know it's not like this in Ottawa. For example, you can get a pretty big fine if you cut out a section of curb to widen your driveway entrance.

I read somewhere (Atlas Obscura?) that there are some hollow sidewalks in NYC, and the sidewalk-adjacent property owners pay for the real estate underneath. To get around this, some owners have sealed off access from their building to the sub-sidewalk spaces, leaving closed off, empty chambers.

Everywhere I've lived in California, you own to the middle of the street, and the sidewalk and streets are easements. Here in Oakland, the property owner is responsible to maintain the sidewalk even.

Property rights don't extend down to the core of the earth unless they're explicit. You have to be careful about this when purchasing land, often times what you're purchasing is the rights down to a certain depth.

A great example of this is oil. When an oil company installs a pump, one of the things they have to do is get agreement from everyone who has mineral rights down to the depths where the oil is. This can get extremely messy, and can often involve people who are not technically the land owners.

I imagine it's a similar situation here, although it could also be that the city simply has an easement on the land itself.

While true, the "certain depth" you speak of is guaranteed to be below the 1" of the article's examples.

But it would be interesting how realistic it is to just excavate from your cellar into other territory. Considering quite a few bank heists have succeeded that way, it might well escape detection for a while.

"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."

Perhaps the inspiration behind this? https://www.bbc.com/news/magazine-23536914

Possibly, or an independent invention from first principles; you'd have to ask the guy.

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.

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.

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

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

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

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

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.

The house we live in (from 1903) still has the original gas lines everywhere. That means there is a hook in the middle of the ceiling connected to the gas pipes for you to hang your gas lantern, but also one or two wall outlets in every room for those.

I suppose the neighbouring houses all had those de-installed, but our electricity installation is from ~1930 as well, so the owners were never fond of renovations, it seems. (It works surprisingly well for its age.) I often wonder about the people who lived here and their lifestyles.

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

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.

About a million years

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

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

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

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

Also, anyone else having flashbacks to Dinotopia sunstones?

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?

These are ubiquitous in London

And many other parts of the UK. I've seen a fair amount in both Oxford and Nottingham.

Plenty up north too. Don't ever remember seeing a purple one though, pretty much always the green you'd expect of very thick glass.

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...

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

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...

(go to page 54 of the .pdf)

Lots of them all over Scotland, too.

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

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

Presumable cost or manufacturability? Big sheets of glass were not feesible in the 1800s

Tempered glass is relatively modern. They didn't have strong solid single panes of glass back then; the concrete with glass inlays was the best way to make it stand up to traffic above.

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.

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.

The earliest patent of deck lights, which predate vault lights or sidewalk prisms, is from 1684.

This site includes some images and patents https://glassian.org/Prism/index.html

There's a patent for sidewalk prisms from 1834.

As other people have said, the glass broke.

> In 1834, Edward Rockwell patented a round iron plate with a single large lens, but Hyatt later complained in his own patent application, "These glasses are extremely liable to fracture, and when broken leave large and dangerous openings within their rims...". Rockwell's plates are rare today; I know of only three examples of the iron covers and none of the lenses

Avoid peeping toms.

The individual pieces were shaped to diffuse the light so that regardless of the direction of the sun, you get a more or less uniform glow inside. This is much easier to do with multiple lenses/prisms than with a single large piece.

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!

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.

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

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

They look like "Dinotopia" Sunstones.

Or "Land of the Lost" crystals:

https://landofthelost.fandom.com/wiki/Crystals

especially as seen in matrix tables in the pylons:

https://landofthelost.fandom.com/wiki/Pylons

Research mudflood to go way down this rabbit hole.

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